0000950170-23-009318 | 10-K | XBRL Viewer

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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2022	Mar. 20, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Trading Symbol	SLDB
Title of 12(b) Security	Common Stock $0.001 par value per share
Security Exchange Name	NASDAQ
Entity Registrant Name	Solid Biosciences Inc.
Entity Central Index Key	0001707502
Current Fiscal Year End Date	--12-31
Entity File Number	001-38360
Entity Tax Identification Number	90-0943402
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	500 Rutherford Avenue, Third Floor
Entity Address, City or Town	Charlestown
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02129
City Area Code	617
Local Phone Number	337-4680
Document Annual Report	true
Document Transition Report	false
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		19,573,132
Entity Public Float			$ 46.2
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
ICFR Auditor Attestation Flag	false
Auditor Firm ID	238
Auditor Name	PricewaterhouseCoopers LLP
Auditor Location	Boston, Massachusetts
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE The registrant intends to file a definitive proxy statement pursuant to Regulation 14A within 120 days of the end of the fiscal year ended December 31, 2022. Portions of such definitive proxy statement are incorporated by reference into Part III of this Annual Report on Form 10-K.

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 155,384	$ 119,136
Available-for-sale securities	58,338	88,643
Prepaid expenses and other current assets	5,916	14,723
Accounts receivable - related party		110
Total current assets	219,638	222,612
Operating lease, right-of-use asset	28,949	1,142
Property and equipment, net	9,657	6,462
Other non-current assets	175	94
Restricted cash	1,833	2,070
Total assets	260,252	232,380
Current liabilities:
Accounts payable	3,238	4,463
Accrued expenses	16,691	9,528
Operating lease liabilities	1,897	1,263
Finance liabilities and finance lease liabilities	668	232
Deferred revenue - related party		8,080
Other current liabilities	14	35
Total current liabilities	22,508	23,601
Operating lease liabilities, excluding current portion	24,279	275
Finance liabilities and finance lease obligations, excluding current portion	1,703	293
Other non-current liabilities	96
Total liabilities	48,586	24,169
Commitments and Contingencies (Note 12)
Stockholders’ Equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized at December 31, 2022 and December 31, 2021; no shares issued and outstanding at December 31, 2022 and December 31, 2021
Common stock, $0.001 par value; 60,000,000 shares authorized at December 31, 2022 and 20,000,000 shares authorized at December 31, 2021; 19,556,732 shares issued and outstanding at December 31, 2022 and 7,356,017 shares issued and outstanding at December 31, 2021; 0 pre-funded warrants outstanding at December 31, 2022 and 143,888 pre-funded warrants outstanding at December 31, 2021	20	7
Additional paid-in capital	774,452	685,006
Accumulated other comprehensive loss	(68)	(45)
Accumulated deficit	(562,738)	(476,757)
Total stockholders' equity	211,666	208,211
Total liabilities and stockholders' equity	$ 260,252	$ 232,380

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	60,000,000	20,000,000
Common stock, shares issued	19,556,732	7,356,017
Common stock, shares outstanding	19,556,732	7,356,017
Pre-funded warrants outstanding	0	143,888

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Statement [Abstract]
Revenue	$ 8,094	$ 13,620
Operating expenses:
Research and development	78,420	58,739	$ 64,881
General and administrative	28,948	27,135	21,581
Restructuring expense	7,178		1,944
Total operating expenses	114,546	85,874	88,406
Loss from operations	(106,452)	(72,254)	(88,406)
Other income, net:
Interest income, net	2,616	64	115
Gain on acquisition	18,236
Other (loss) income, net	(381)	2	1
Total other income, net	20,471	66	116
Net loss	$ (85,981)	$ (72,188)	$ (88,290)
Net loss per share, basic	$ (10.10)	$ (10.14)	$ (25.50)
Net loss per share, diluted	$ (10.10)	$ (10.14)	$ (25.50)
Weighted average common stock outstanding basic	8,512,089	7,118,024	3,462,475
Weighted average common stock outstanding, diluted	8,512,089	7,118,024	3,462,475

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Statement of Comprehensive Income [Abstract]
Net loss	$ (85,981)	$ (72,188)	$ (88,290)
Other comprehensive loss:
Unrealized loss on available-for-sale securities	(23)	(45)	(1)
Comprehensive loss	$ (86,004)	$ (72,233)	$ (88,291)

- Definition

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income. Excludes changes in equity resulting from investments by owners and distributions to owners.

+ References + Details

- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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+ Details

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2019	$ 80,048	$ 3	$ 396,323	$ 1	$ (316,279)
Beginning balance, units at Dec. 31, 2019		3,218,884
Equity-based compensation	11,629		11,629
Sale of common stock, net of issuance costs	109,418	$ 2	109,416
Sale of common stock, net of issuance costs, shares		2,042,263
Issuance of common stock, to a related party, in connection with the Stock Purchase Agreement	19,282	$ 1	19,281
Issuance of common stock, to a related party, in connection with the Stock Purchase Agreement, shares		521,719
Vesting of restricted stock units		27,180
Forfeiture of restricted stock awards units		(6,559)
Unrealized loss on available-for-sale securities	(1)			(1)
Net loss	(88,290)				(88,290)
Ending balance at Dec. 31, 2020	132,086	$ 6	536,649		(404,569)
Ending balance, units at Dec. 31, 2020		5,803,487
Equity-based compensation	13,373		13,373
Sale of common stock, net of issuance costs	134,878	$ 1	134,877
Sale of common stock, net of issuance costs, shares		1,666,666
Exercise of common stock options	41		41
Exercise of common stock options, shares		775
Issuance of ESPP shares	66		66
Issuance of ESPP shares, shares		2,978
Vesting of restricted stock units		27,946
Forfeiture of restricted stock awards units		(1,947)
Unrealized loss on available-for-sale securities	(45)			(45)
Net loss	(72,188)				(72,188)
Ending balance at Dec. 31, 2021	208,211	$ 7	685,006	(45)	(476,757)
Ending balance, units at Dec. 31, 2021		7,499,905
Equity-based compensation	7,537		7,537
Sale of common stock, net of issuance costs	72,551	$ 11	72,540
Sale of common stock, net of issuance costs, shares		10,638,290
Exercise of pre-funded warrants	22		22
Issuance of ESPP shares	181	$ 1	180
Issuance of ESPP shares, shares		29,130
Vesting of restricted stock units		35,149
Issuance of shares in connection with acquisition	9,168	$ 1	9,167
Issuance of shares in connection with acquisition, shares		1,354,258
Unrealized loss on available-for-sale securities	(23)			(23)
Net loss	(85,981)				(85,981)
Ending balance at Dec. 31, 2022	$ 211,666	$ 20	$ 774,452	$ (68)	$ (562,738)
Ending balance, units at Dec. 31, 2022		19,556,732

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Issuance costs	$ 2,449	$ 8,872	$ 3,790

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Operating activities:
Net loss	$ (85,981)	$ (72,188)	$ (88,290)
Adjustments to reconcile net loss to net cash used in operating activities:
Net amortization of premium/(discount) on available-for-sale securities	233	1,117	(20)
Equity-based compensation expense	7,537	13,373	11,629
Depreciation and amortization expense	2,408	2,964	3,922
Loss on sale of property and equipment		92
Gain on lease termination	(249)	(81)
Gain on acquisition	(18,236)
Changes in operating assets and liabilities:
Prepaid expenses and other current and non-current assets	3,695	(9,247)	30
Accounts receivable - related party	110	(110)
Accounts payable	(5,246)	1,209	(3,431)
Accrued expenses and other current and non-current liabilities	5,832	(2,255)	(1,157)
Deferred revenue - related party, current and non-current	(8,080)	(12,638)	20,718
Net cash used in operating activities	(97,977)	(77,764)	(56,599)
Investing activities:
Purchases of property and equipment	(3,015)	(1,281)	(899)
Acquisition of business, net of cash received	31,523
Proceeds from sale of property and equipment	600
Proceeds from sales and maturities of available-for-sale securities	212,811	51,444	7,900
Purchases of available-for-sale securities	(182,762)	(141,249)	(401)
Net cash provided by (used in) investing activities	59,157	(91,086)	6,600
Financing activities:
Proceeds from the issuance of common stock to a related party in connection with the Stock Purchase Agreement			19,282
Proceeds from issuance of common stock, net of issuance costs	72,551	134,878	113,208
Proceeds from financing liabilities	2,143
Payment of offering costs			(3,790)
Proceeds for exercise of stock options		41
Proceeds from exercise of pre-funded warrants	22
Employee stock purchases and withholdings	181	66
Repayment of financing liabilities	(66)
Net cash provided by financing activities	74,831	134,985	128,700
Net increase (decrease) in cash, cash equivalents and restricted cash	36,011	(33,865)	78,701
Cash, cash equivalents, and restricted cash at beginning of period	121,206	155,071	76,370
Cash, cash equivalents, and restricted cash at end of period	157,217	121,206	155,071
Supplemental disclosure of non-cash investing and financing activities:
Issuance of common stock in acquisition	9,168
Decrease in right-of-use assets and lease liability due to lease termination	(464)	(1,233)
Right-of-use assets obtained in exchange for operating lease liabilities	29,126	310	1,629
Property and equipment included in accounts payable and accruals	$ 527	$ 104	$ 20

Nature of the Business and Basis of Presentation

12 Months Ended

Dec. 31, 2022

Accounting Policies [Abstract]

Nature of the Business and Basis of Presentation

1. Nature of the Business and Basis of Presentation

Nature of Business

Solid Biosciences Inc. was organized in March 2013 under the name SOLID Ventures Management, LLC and operated as a Delaware limited liability company until immediately prior to the effectiveness of its registration statement on Form S-1 on January 25, 2018, at which time it completed a statutory corporate conversion into a Delaware corporation (the “Corporate Conversion”) and changed its name to Solid Biosciences Inc. (the “Company”). On December 2, 2022, the Company completed its acquisition of AavantiBio, Inc. (“AavantiBio”), a privately held gene therapy company focused on transforming the lives of patients with Friedreich’s ataxia ("FA") and rare cardiomyopathies (the “Acquisition”). Upon the consummation of the acquisition, the Company acquired AavantiBio’s candidates, AVB-202-TT and AVB-401, as well as additional assets for the treatment of undisclosed cardiac diseases. AavantiBio is a wholly owned subsidiary of the Company.

The Company is a life science company focused on advancing a portfolio of neuromuscular and cardiac programs, including SGT-003, a differentiated gene therapy candidate, for the treatment of Duchenne muscular dystrophy ("Duchenne"); AVB-202-TT, a gene therapy program for the treatment of FA; AVB-401, a gene therapy program for the treatment of BAG3-mediated dilated cardiomyopathy; and additional assets for the treatment of undisclosed cardiac diseases. The Company aims to be a center of excellence, bringing together those with expertise in science, technology, disease management and care. Patient-focused and founded by those directly impacted by Duchenne, the Company's mandate is to improve the daily lives of patients living with these devastating diseases.

The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on licenses, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical studies and clinical trials and regulatory approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel infrastructure and extensive compliance and reporting capabilities.

The Company’s candidates are in development. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, that any products developed will obtain necessary government regulatory approval or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from, among others, other pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees, partners and consultants.

On October 27, 2022, the Company effected a reverse stock split of its outstanding shares of common stock at a ratio of one-for-15 pursuant to a certificate of amendment to its certificate of incorporation filed with the Secretary of State of the State of Delaware. The reverse stock split was reflected on Nasdaq beginning with the opening of trading on October 28, 2022. Pursuant to the reverse stock split, every 15 shares of the Company's issued and outstanding shares of common stock were automatically combined into one issued and outstanding share of common stock, without any change in the par value per share of the common stock. The reverse stock split reduced the authorized number of shares of common stock from 300,000,000 to 20,000,000 and, pursuant to the certificate of amendment, such reduced authorized number of shares of common stock was subsequently multiplied by three, such that following the reverse stock split the Company has 60,000,000 shares of common stock authorized. The reverse stock split affected all issued and outstanding shares of the Company's common stock, and the respective numbers of shares of common stock underlying the Company’s outstanding stock options, outstanding restricted stock units, outstanding warrants and the Company's equity incentive plans were proportionately adjusted. All share and per share amounts of the common stock included in the accompanying consolidated financial statements have been retrospectively adjusted to give effect to the reverse stock split for all periods presented, including reclassifying an amount equal to the reduction in par value to additional paid-in capital.

Liquidity

The accompanying consolidated financial statements have been prepared on a basis that assumes the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business. Through December 31, 2022, the Company has funded its operations primarily with the proceeds from the sale of redeemable preferred units and member units as well as the sale of common stock and prefunded warrants to purchase shares of its common stock in private placements and the sale of common stock in its initial public offering and follow-on public offering in March 2021 and under its at-the-market sales agreement.

On September 29, 2022, the Company entered into the securities purchase agreement, pursuant to which, on December 2, 2022, the Company issued an aggregate of 10,638,290 shares of the Company’s common stock in a private placement. The private placement closed immediately following the closing of the acquisition on December 2, 2022. The Company received net proceeds from the private placement of $72,551.

In accordance with Accounting Standards Codification (“ASC”) 205-40, Going Concern, the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date the financial statements are issued. As of December 31, 2022, the Company had an accumulated deficit of $562,738. During the year ended December 31, 2022, 2021 and 2020, the Company incurred a net loss of $85,981, $72,188 and $88,290, respectively. The Company used $97,977 of cash in operations for the year ended December 31, 2022. The Company expects to continue to generate operating losses in the foreseeable future. Based upon its current operating plan, the Company expects that its cash, cash equivalents and available-for-sale securities of $213,722, excluding restricted cash of $1,833, as of December 31, 2022, will be sufficient to fund its operating expenses and capital expenditure requirements for at least twelve months from the date of issuance of these financial statements. However, the Company has based this estimate on assumptions that may prove to be wrong, and its operating plan may change as a result of many factors currently unknown to it. As a result, the Company could deplete its capital resources sooner than it currently expects. The Company expects to finance its future cash needs through a combination of equity offerings, debt financings, collaborations, strategic alliances or licensing arrangements. If the Company is unable to obtain funding, the Company would be forced to delay, reduce or eliminate some or all of its research and development programs, preclinical and clinical testing or commercialization efforts, which could adversely affect its business prospects.

The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying consolidated financial statements include the accounts of the Company and its wholly owned or controlled subsidiaries. All intercompany accounts and transactions have been eliminated.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2022

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Use of Estimates

The preparation of the Company’s consolidated financial statements in conformity with GAAP requires management to make estimates, judgments and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, estimates related to revenue recognition, the recognition of research and development expenses and equity-based compensation. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from the Company’s estimates.

The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including clinical trials and employee-related amounts, will depend on future developments that are highly uncertain, including new information that may emerge concerning COVID-19 and the actions taken to contain it or treat its impact. The Company has made estimates of the impact of COVID-19 within its financial statements and there may be changes to those estimates in future periods. Actual results could differ from the Company’s estimates.

Cash Equivalents

The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents.

Restricted Cash

The Company held restricted cash of $1,833 and $2,070 in separate restricted bank accounts as security deposits for leases of the Company’s facilities as of December 31, 2022 and December 31, 2021, respectively. The Company has included restricted cash of $1,833 and $2,070 as a non-current asset as of December 31, 2022 and December 31, 2021, respectively. A reconciliation of the amounts of cash and cash equivalents and restricted cash from the cash flow statement to the balance sheet is as follows:


	December 31, 2022		December 31, 2021		December 31, 2020		December 31, 2019
Cash and cash equivalents	$	155,384	$	119,136	$	154,744	$	76,043
Restricted cash, non-current		1,833		2,070		327		327
Cash and cash equivalents and restricted cash	$	157,217	$	121,206	$	155,071	$	76,370

Available-for-Sale Securities

Available-for-sale securities consist of investments with original maturities greater than 90 days at acquisition date. The Company has classified its investments with maturities beyond one year as short term, based on their highly liquid nature and because such available-for-sale securities represent the investment of cash that is available for current operations.

The Company classifies all of its investments as available-for-sale securities. The Company’s investments are measured and reported at fair value using quoted prices in active markets for similar securities. Unrealized gains and losses on available-for-sale debt securities are reported as a separate component of stockholders’ equity. The cost of debt securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense) within the consolidated statement of operations. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary,” the Company reduces the investment to fair value through a charge to the consolidated statement of operations. No such adjustments were necessary during the periods presented.

Concentration of Credit Risk and of Significant Suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and available-for-sale securities. Periodically, the Company maintains deposits in accredited financial institutions in excess of federally insured limits. The Company maintains each of its cash, cash equivalents and available-for-sale securities balances with high-quality and accredited financial institutions and accordingly, such funds are not exposed to significant credit risk. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

The Company is dependent on third-party manufacturers to supply products for research and development activities of its programs, including clinical and preclinical testing. These programs could be adversely affected by a significant interruption in the supply of such drug substance products.

Fair Value Measurements

Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:

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Level 1—Quoted prices in active markets for identical assets or liabilities.

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Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities or other inputs that are observable or can be corroborated by observable market data.

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Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

The Company’s cash equivalents and available-for-sale securities are carried at fair value, determined according to the fair value hierarchy described above. See Note 5, Fair Value of Financial Assets and Liabilities, for additional information. The carrying values of the Company’s accounts payable and accrued expenses and other current liabilities approximate their fair value due to the short-term nature of these liabilities.

Leases

At inception of a contract, the Company determines if a contract meets the definition of a lease. A lease is a contract, or part of a contract, that conveys the right to control the use of identified property, plant, or equipment (an identified asset) for a period of time in exchange for consideration. The Company determines if the contract conveys the right to control the use of an identified asset for a period of time. The Company assesses throughout the period of use whether the Company has both of the following: (1) the right to obtain substantially all of the economic benefits from use of the identified asset and (2) the right to direct the use of the identified asset. This determination is reassessed if the terms of the contract are changed. Leases are classified as operating or finance leases based on the terms of the lease agreement and certain characteristics of the identified asset. Right-of-use assets and lease liabilities are recognized at the lease commencement date based on the present value of the minimum future lease payments. Adjustments to the right-of-use asset may be required for items such as lease prepayments or incentives received. The Company’s policy is to not record leases with an original term of twelve months or less on the consolidated balance sheets. The Company recognizes lease expense for these short-term leases on a straight-line basis over the lease term. Certain lease agreements include rental payments that are adjusted periodically for inflation or other variables. In addition to rent, the leases may require the Company to pay additional amounts for taxes, insurance, maintenance and other expenses, which are generally referred to as non-lease components. Such adjustments to rental payments and variable non-lease components are treated as variable lease payments and recognized in the period in which the obligation for these payments was incurred. Variable lease components and variable non-lease components are not measured as part of the right-of-use asset and liability. Only when lease components and their associated non-lease components are fixed are they accounted for as a single lease component and recognized as part of a right-of-use asset and liability. Total contract consideration is allocated to the combined fixed lease and non-lease components.

Property and Equipment

Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the useful life of the asset. Laboratory equipment is depreciated over five years. Computer equipment is depreciated over three years. Computer software is depreciated over two years. Furniture and office equipment are depreciated over five years. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the related asset. Expenditures for repairs and maintenance of assets are charged to expense as incurred. Upon retirement or sale, the cost and related accumulated depreciation of assets disposed of are removed from the accounts and any resulting gain or loss is included in loss from operations. Equipment under a finance lease is stated at fair value at the inception of the lease less accumulated depreciation and is depreciated over the remaining lease term or the estimated useful life of the equipment.

Impairment of Long-Lived Assets

Long-lived assets, comprised of property and equipment, to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. To date, the Company has not recorded any impairment losses or disposals on long-lived assets.

Revenue Recognition

The Company recognizes revenue in accordance with ASC Topic 606, Revenue from Contracts with Customers (“ASC 606”). Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine the appropriate amount of revenue to be recognized for arrangements determined to be within the scope of ASC 606, the Company performs the following five steps: (i) identification of the contract(s) with the customer; (ii) identification of the promised goods or services in the contract and determination of whether the promised goods or services are performance obligations; (iii) measurement of the transaction price; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied.

As part of the accounting for these arrangements, the Company must use significant judgment to determine: a) the number of performance obligations based on the determination under step (ii) above and whether those performance obligations are distinct from other performance obligations in the contract; b) the transaction price under step (iii) above; and c) the standalone selling price for each performance obligation identified in the contract for the allocation of transaction price in step (iv) above. The Company uses judgment to determine whether milestones or other variable consideration, except for royalties, should be included in the transaction price as described further below. The transaction price is allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. In determining the stand-alone selling price of a license to the Company’s proprietary technology or a material right provided by a customer option, the Company considers market conditions as well as entity-specific factors, including those factors contemplated in negotiating the agreements as well as internally developed estimates that include assumptions related to the market opportunity, estimated development costs, probability of success and the time needed to commercialize a product candidate pursuant to the license. In validating its estimated stand-alone selling prices, the Company evaluates whether changes in the key assumptions used to determine its estimated stand-alone selling prices will have a significant effect on the allocation of arrangement consideration between performance obligations.

The Company estimates the transaction price based on the amount of consideration the Company expects to be received for transferring the promised goods or services in the contract. The consideration may include both fixed consideration and variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of the potential payments and the likelihood that the payments will be received. The Company utilizes either the most likely amount method or expected value method to estimate the transaction price based on which method better predicts the amount of consideration expected to be received. If it is probable that a significant reversal in the amount of cumulative revenue recognized would not occur, the variable consideration is included in the transaction price.

Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer. Promised goods or services are considered distinct when: (i) the customer can benefit from the good or service on its own or together with other readily available resources and (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised goods or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on their own and whether the required expertise is readily available.

For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation in order to determine whether the combined performance obligation is satisfied over time or at a point in time. Up-front payments and fees are recorded as deferred revenue upon receipt or when due until the Company performs its obligations under these arrangements. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current portion of deferred revenue in the accompanying consolidated balance sheets. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. Amounts recognized as revenue, but not yet received or invoiced are generally recognized as contract assets.

Exclusive Licenses

If the license granted in the arrangement is determined to be distinct from the other promises or performance obligations identified in the arrangement, which generally include research and development services, the Company recognizes revenue from non-refundable, upfront fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license In assessing whether a license is distinct from the other promises, the Company considers relevant facts and circumstances of each arrangement, including the research and development capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can benefit from the license for its intended purpose without the receipt of the remaining promise, whether the value of the license is dependent on the unsatisfied promise, whether there are other vendors that could provide the remaining promise, and whether it is separately identifiable from the remaining promise. For licenses that are combined with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The measure of progress, and thereby periods over which revenue should be recognized, are subject to estimates by management and may change over the course of the arrangement.

Research and Development Services

The promises under the Company’s collaboration and license agreements generally include research and development services to be performed by the Company on behalf of the collaboration partner. For performance obligations that include research and development services, the Company generally recognizes revenue allocated to such performance obligations based on an appropriate measure of progress. The Company utilizes judgment to determine the appropriate method of measuring progress for purposes of recognizing revenue, which is generally an input measure, such as costs incurred.

Milestone Payments

At the inception of each arrangement that includes milestone payments based on certain events, the Company evaluates whether the milestones are considered probable of being achieved and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant reversal in the amount of cumulative revenue recognized would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the particular milestone in making this assessment. There is considerable judgment involved in determining whether it is probable that a significant reversal in the amount of cumulative revenue recognized would not occur. At the end of each subsequent reporting period, the Company reevaluates the probability of achievement of all milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. If a milestone or other variable consideration relates specifically to the Company’s efforts to satisfy a single performance obligation or to a specific outcome from satisfying the performance obligation, the Company generally allocates the milestone amount entirely to that performance obligation once it is probable that a significant reversal in the amount of cumulative revenue recognized would not occur.

Royalties

For arrangements that include sales-based royalties, including milestone payments based on a level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its licensing arrangements.

Collaboration Revenue

The Company analyzes its collaboration arrangements to assess whether they are within the scope of ASC 808, Collaborative Arrangements (“ASC 808”) to determine whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For collaboration arrangements within the scope of ASC 808 that contain multiple elements, the Company first determines which elements of the collaboration are deemed to be within the scope of ASC 808 and those that are more reflective of a vendor-customer relationship and therefore within the scope of ASC 606. For elements of collaboration arrangements that are accounted for pursuant to ASC 808, an appropriate recognition method is determined and applied consistently, generally by analogy to ASC 606. For those elements of the arrangement that are accounted for pursuant to ASC 606, the Company applies the five-step model described above.

Costs Associated with License and Collaborative Arrangements

All costs associated with license and collaborative arrangements are expensed as incurred and recorded in research and development expense in the consolidated statements of operations.

Research and Development Costs

Research and development costs are expensed as incurred. Research and development expenses include salaries, equity-based compensation and benefits of employees, third-party license fees and other operational costs related to the Company’s research and development activities, including allocated facility-related expenses and external costs of outside vendors engaged to conduct both preclinical studies and clinical trials. Non-refundable pre-payments for goods or services that will be used or rendered for future research and development activities are deferred and capitalized. Such amounts are recognized as expense as the goods or services are delivered or the related services are performed, or until it is no longer expected that the goods will be delivered or the services rendered.

The Company may in-license the rights to develop and commercialize product candidates. For each in-license transaction the Company evaluates whether it has acquired processes or activities along with inputs that would be sufficient to constitute a “business” as defined under GAAP. A “business” as defined under GAAP consists of inputs and processes applied to those inputs that have the ability to create outputs. Although businesses usually have outputs, outputs are not required for an integrated set of activities to qualify as a business. When the Company determines that it has not acquired sufficient processes or activities to constitute a business, any up-front payments, as well as milestone payments, are immediately expensed as acquired research and development in the period in which they are incurred.

Research Contract Costs and Accruals

The Company has entered into various research and development contracts with research institutions and other companies. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.

Patent Costs

All patent-related costs incurred for filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses.

Equity-Based Compensation

The Company measures all stock options and other stock-based awards granted to employees, directors and non-employees based on the fair value on the date of the grant and recognizes compensation expense of those awards, over the requisite service period, which is generally the vesting period of the respective award. Forfeitures are accounted for as they occur. The Company applies the straight-line method of expense recognition to all awards with only service-based vesting conditions. The Company has not issued any awards with performance-based vesting conditions.

The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company historically has been a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. For options with service-based vesting conditions, the expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. Through December 31, 2018, the expected term of stock options granted to non-employees is equal to the contractual term of the option award and effective January 1, 2019, the “simplified” method is used. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future.

The fair value for restricted stock units (“RSU”) was calculated using the closing price of the Company’s common stock on the date of grant.

The Company classifies stock-based compensation expense in its consolidated statement of operations in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.

Income Taxes

Income taxes are accounted for under the asset and liability method. Under the asset and liability method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. The Company records valuation allowances to reduce deferred income tax assets to the amount that is more likely than not to be realized. The Company determines whether it is more likely than not that a tax position will be sustained upon examination. If it is not more likely than not that a position will be sustained, no amount of benefit attributable to the position is recognized. The tax benefit to be recognized of any tax position that meets the more likely than not recognition threshold is calculated as the largest amount that is more than 50% likely of being realized upon resolution of the contingency.

Prior to January 25, 2018, the Company had not been subject to U.S. federal income taxes as the Company was organized as a limited liability company. As such, the taxable income or loss was passed through to and included in the tax returns of the members. Since January 25, 2018, the Company’s income has since been subject to U.S. federal, state, local, and foreign income taxes and taxed at the prevailing corporate tax rates.

Segment Data

The Company currently manages its operations as a single segment for the purposes of assessing performance and making operating decisions. All of the Company’s tangible assets are held in the United States.

Comprehensive Loss

Comprehensive loss includes net loss, as well as other changes in stockholders’ equity that result from transactions and economic events other than those with members. The Company’s only element of other comprehensive income (loss) in all periods presented was unrealized gains (losses) from available-for-sale securities.

Net Loss per Share

The Company follows the two-class method when computing net loss per share, as the Company has issued shares that meet the definition of participating securities. The two-class method determines net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and

participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed.

Basic net loss per share is computed by dividing the net loss by the weighted average number of shares of common stock and pre-funded warrants outstanding for the period. Diluted net loss is computed by adjusting net loss to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net loss per share is computed by dividing the diluted net loss by the weighted average number of shares of common stock and pre-funded warrants outstanding for the period, including potential dilutive shares of common stock assuming the dilutive effect of common stock equivalents.

The Company’s preferred stock could entitle the holders of such shares to participate in dividends and not require the holders of such shares to participate in losses of the Company. Accordingly, in periods in which the Company reports a net loss, such losses are not allocated to such participating securities. In periods in which the Company reports a net loss, diluted net loss per share is the same as basic net loss per share, since dilutive shares of common stock are not assumed to have been issued if their effect is anti-dilutive. As of the year ended December 31, 2022 and 2021, there were no preferred stock issued or outstanding with any contractual rights.

Contingencies

Loss contingency provisions are recorded if the potential loss from any claim, asserted or unasserted, or legal proceeding, is considered probable and the amount can be reasonably estimated, or a range of loss can be determined. These accruals represent the Company’s best estimate of probable loss. Disclosure also is provided when it is reasonably possible that a loss will be incurred or when it is reasonably possible that the amount of a loss will exceed the recorded provision. The Company reviews the status of each significant matter and assesses its potential financial exposure. Significant judgment is required in both the determination of probability and the determination as to whether an exposure is reasonably estimable. Because of uncertainties related to these matters, accruals are based only on the best information available at the time. As additional information becomes available, the Company reassesses the potential liability related to pending claims and may change its estimates. These changes in the estimates of the potential liabilities could have a material impact on the Company’s consolidated results of operations and financial position.

Business Combinations

The Company's consolidated financial statements include the operations of acquired businesses after the completion of the acquisitions. The Company accounts for acquired businesses using the acquisition method of accounting. Application of this method of accounting requires that (i) identifiable assets acquired (including identifiable intangible assets) and liabilities assumed be measured and recognized at fair value as of the acquisition date, and (ii) the excess of the purchase price over the net fair value of identifiable assets acquired and liabilities assumed be recorded as goodwill. Acquired in-process research and development (“IPR&D”) is recognized at fair value and initially characterized as an indefinite-lived intangible asset, irrespective of whether the acquired IPR&D has an alternative future use. Transaction costs are expensed as incurred. Amounts assigned to goodwill and other identifiable intangible assets are based on independent appraisals or internal estimates.

Related Party

In October 2020, the Company entered into a collaboration and license agreement (the “Collaboration Agreement”) with Ultragenyx Pharmaceutical Inc. (“Ultragenyx”). In connection with the Collaboration Agreement, Ultragenyx also purchased 521,719 shares of the Company’s common stock, which resulted in Ultragenyx becoming a related party of the Company.

In November 2020, the Company entered into a consulting agreement with Danforth Advisors, LLC (“Danforth”), an affiliate of Stephen DiPalma, who previously served as the Company’s interim chief financial officer. Pursuant to the consulting agreement, Danforth provided the Company with the chief financial officer services of Mr. DiPalma, and other services, including financial planning, offering support and accounting services, in exchange for fees payable to Danforth based on hourly rates. The Company has paid Danforth approximately $1,965 as of December 31, 2022. During the years ended December 31, 2022 and 2021, the Company incurred cost of $1,472 and $777, respectively, related to the consulting agreement. In accordance with the consulting agreement, in November 2020, the Company issued to Danforth a warrant to purchase 2,000 shares of its common stock at an exercise price per share of $49.35. As of December 31, 2022, the warrants had vested in full.

Recently Adopted Accounting Pronouncements

In December 2019, the Financial Accounting Standards Board (“FASB") issued Accounting Standards Update (“ASU”) No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which simplifies the accounting for income taxes by removing certain exceptions to the general principles in ASC 740 and clarifies and amends existing guidance to improve consistent application. The standard became effective for the Company beginning January 1, 2021. The amendments that are related to changes in ownership of foreign equity method investments or foreign subsidiaries are to be applied on a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the fiscal year of adoption. The amendments that are related to franchise taxes that are partially based on income are to be applied on either a retrospective basis for all periods presented or a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the fiscal year of adoption. All other amendments under this ASU are to be applied on a prospective basis. The Company adopted the guidance effective January 1, 2021. The adoption of this new standard did not have a material impact on the Company’s financial statements.

Recently Issued Accounting Pronouncements

In August 2020, the FASB issued ASU No. 2020-06, Debt, Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity, which, among other things, provides guidance on how to account for contracts on an entity’s own equity. This ASU simplifies the accounting for certain financial instruments with characteristics of liabilities and equity. Specifically, the ASU eliminated the need for the Company to assess whether a contract on the entity’s own equity (1) permits settlement in unregistered shares, (2) whether counterparty rights rank higher than shareholder’s rights, and (3) whether collateral is required. In addition, the ASU requires incremental disclosure related to contracts on the entity’s own equity and clarifies the treatment of certain financial instruments accounted for under this ASU on earnings per share. The ASU also simplifies the accounting for convertible instruments by removing the beneficial conversion feature and cash conversion feature separation models. This ASU may be applied on a full retrospective or modified retrospective basis. This ASU is effective for smaller reporting companies for fiscal years beginning after December 15, 2023, with early adoption permitted. The Company does not expect the adoption to materially impact its financial position and results of operations.

Collaborations

12 Months Ended

Dec. 31, 2022

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Collaborations

3. Collaborations

Ultragenyx Collaboration

Collaboration Agreement

On October 22, 2020 (the “Effective Date”), the Company entered into the Collaboration Agreement with Ultragenyx to focus on the development and commercialization of new gene therapies for Duchenne. The Company granted Ultragenyx an exclusive worldwide license for any pharmaceutical product that expresses the Company’s proprietary microdystrophin construct from AAV8 and variants thereof in clade E for the treatment of Duchenne and other diseases resulting from the lack of functional dystrophin (the “Licensed Products”). The Company retains exclusive rights to all other uses of its microdystrophin proteins, including under its SGT-001 and SGT-003 programs.

The Company has conducted certain research and development activities with respect to the development of the Licensed Products, and concluded such activities as were contemplated under the Collaboration Agreement during the second quarter of 2022, resulting in the recognition of the remaining deferred revenue recorded at the time the Collaboration Agreement was executed, related to the upfront payment received from Ultragenyx. The Company may conduct additional research and development activities in collaboration with Ultragenyx from time to time in the future. Ultragenyx reimbursed the Company for personnel and out-of-pocket costs that the Company incurred in conducting such activities.

In addition, Ultragenyx granted to the Company an exclusive Development Option or Income Share Option (each as defined and described below) exercisable in the Company’s sole discretion one time per Licensed Product. After the date of first achievement of clinical proof of concept, Ultragenyx will provide to the Company a data package with respect to the relevant Licensed Product. The Company will use the data package to determine whether to exercise the corresponding Development Option or Income Share Option with respect to such Licensed Product.

With respect to each Licensed Product for which the Company has not exercised the Development Option or Income Share Option the Company will be entitled to milestone payments of up to $25,000 in the aggregate for each such Licensed Product that achieves specified development milestones and $65,000 in the aggregate for each such Licensed Product that achieves specified regulatory milestones. With respect to each Licensed Product for which the Company has not exercised the Income Share Option, the Company will also be entitled to milestone payments of up to $165,000 in the aggregate for each Licensed Product that achieves specified annual worldwide net sales milestones. For Licensed Products for which the Company has not

exercised the Development Option or Income Share Option, Ultragenyx will pay the Company tiered royalties on a Licensed Product-by-Licensed Product and country-by-country basis ranging from a low double-digit percentage to a mid-teens percentage based on Ultragenyx’s annual worldwide net sales of such Licensed Products.

For each Licensed Product for which Ultragenyx decides to initiate a registrational trial in humans, the Company will have the option to fund 30% of the development costs in the United States and European Union for such Licensed Product and forgo the development and regulatory milestones (the “Development Option”) and receive tiered royalties on a Licensed Product-by-Licensed Product and country-by-country basis ranging from a mid-teens percentage to a low twenties percentage based on Ultragenyx’s annual worldwide net sales of each such Licensed Product.

For each Licensed Product for which the Company exercises the Development Option, the Company may also elect to share 30% of the net income and net losses on net sales of such Licensed Product in the United States and European Union (the “Income Share Option”). For Licensed Products for which the Company has exercised the Income Share Option, the Company will not be entitled to milestone payments and Ultragenyx will pay the Company tiered royalties on a Licensed Product-by-Licensed Product and country-by-country basis ranging from a mid-teens percentage to a low twenties percentage based on Ultragenyx’s annual net sales of each such Licensed Product outside of the United States and European Union.

The Company may only exercise an Income Share Option if neither the Company nor any of its affiliates is then developing or commercializing a product that is competitive with the Licensed Product that is subject to such option. If the Company or any of its affiliates subsequently develops or commercializes a product that is competitive with a Licensed Product for which the Company has exercised an Income Share Option, then the Company and Ultragenyx will no longer share the net income and net losses on net sales of such Licensed Product and such Licensed Product will be treated as if the Company had exercised the Development Option with respect to such Licensed Product.

Following the Company’s exercise of the Development Option or Income Share Option with respect to a Licensed Product, the Company also has the right to cease participation in the sharing of development costs and sharing in net income and net losses on net sales, as applicable, for such Licensed Product by written notice to Ultragenyx. Upon such notice, the Company will no longer share in the development costs and net income and net losses on net sales of such Licensed Product, as applicable, and will be eligible to receive payments on milestones achieved after the opt-out for such Licensed Product and royalties at the rates applicable to Licensed Products for which the Company has not exercised the Development Option or Income Share Option, as described above.

The Collaboration Agreement continues on a country-by-country and Licensed Product-by-Licensed Product basis until the expiration of all payment obligations under the agreement. With respect to any Licensed Product for which the Company has exercised an Income Share Option, the Collaboration Agreement continues until there are no longer sales of such Licensed Product in the United States or Europe. Either party has the right to terminate the agreement if the other party has materially breached in the performance of its obligations under the agreement and such breach has not been cured within the applicable cure period. Ultragenyx may also terminate the Collaboration Agreement in its sole discretion upon 90 days’ prior written notice to the Company.

Stock Purchase Agreement

In connection with the execution of the Collaboration Agreement, Ultragenyx and the Company also entered into a stock purchase agreement (the “Stock Purchase Agreement”) on the Effective Date, pursuant to which the Company issued and sold 521,719 shares of its common stock (the “Shares”) to Ultragenyx at a price of $76.6695 per share for an aggregate purchase price of approximately $40,000. The Stock Purchase Agreement contains customary representations, warranties and covenants of each of the parties thereto. Following the sale of the Shares, Ultragenyx beneficially owned approximately 14.45% of the Company’s outstanding common stock. As of December 31, 2022, Ultragenyx beneficially owned approximately 2.7% of the Company’s outstanding common stock.

Investor Agreement

In connection with the consummation of the transactions contemplated by the Stock Purchase Agreement, the Company and Ultragenyx entered into an Investor Agreement (the “Investor Agreement”) on the Effective Date. Pursuant to the terms of the Investor Agreement, Ultragenyx agreed that, so long as it holds at least 10% of the Company’s outstanding common stock, the Shares will be subject to a voting agreement, such that until the earliest to occur of certain specified events, and subject to specified conditions, Ultragenyx will, and will cause its permitted transferees to, vote in accordance with the recommendation of the Company’s Board of Directors with respect to specified matters.

Accounting Treatment

The Company concluded that the Collaboration Agreement and the Stock Purchase Agreement should be combined and treated as a single arrangement for accounting purposes as the agreements were entered into contemporaneously and in contemplation of one another.

The Company assessed this arrangement in accordance with ASC 606 and concluded that the contract counterparty, Ultragenyx, is a customer. The Company identified the following promises in the Collaboration Agreement that were evaluated under the scope of ASC 606: (1) an exclusive worldwide license to the Licensed Products; (2) an obligation to perform research and development services; and (3) an obligation to participate in a joint steering committee. The Company assessed the promised goods and services to determine if they are distinct. Based on this assessment, the Company determined that Ultragenyx cannot benefit from the promised goods and services separately from the others as they are highly interrelated and therefore not distinct. Due to the early stage of the Licensed Products, the research and development services could not be performed by another party. The Company’s skill-set, knowledge and expertise are required to conduct the research and development services and the research and development services are expected to involve significant further development of the Licensed Products. Accordingly, the promised goods and services represent one combined performance obligation and the entire transaction price will be allocated to that single combined performance obligation.

The Company determined the transaction price under ASC 606 at the inception of the Collaboration Agreement to be $22,513, which represents the excess proceeds from the equity investment under the Stock Purchase Agreement, when measured at fair value after taking into consideration a discount for lack of marketability, plus the estimated reimbursement of research and development costs, which represents variable consideration. The Company included the estimated reimbursement of research and development costs in the transaction price at the inception of the arrangement because the Company is required to perform research and development services and the contract requires Ultragenyx to reimburse the Company for costs incurred. Also, since the related revenue would be recognized only as the costs are incurred, the Company determined it is not probable that a significant reversal of cumulative revenue would occur. The Company evaluated how much variable consideration related to development and regulatory milestones, and the Company’s potential exercise of its Development Option or Income Share Option per Licensed Product, to include in the transaction price using the most likely amount approach and concluded that no amount should be included in the transaction price due to the high degree of uncertainty and risk associated with these potential payments. The Company also determined that royalties and sales milestones relate solely to the license of intellectual property and are therefore excluded from the transaction price under the sales- or usage-based royalty exception of ASC 606. Revenue related to these royalties and sales milestones will only be recognized when the associated sales occur, and relevant thresholds are met.

The Company determined that revenue under the Collaboration Agreement should be recognized over time as Ultragenyx simultaneously receives the benefit from the Company as the Company performs under the single performance obligation over time. The Company will recognize revenue for the single performance obligation using a cost-to-cost input method as the Company has concluded it best depicts the research and development and joint steering committee participation services performed. Under this method, the transaction price is recognized over the contract’s entire performance period, using costs incurred relative to total estimated costs to determine the extent of progress towards completion.

Ultragenyx is a related party because Ultragenyx was one of the Company’s significant stockholders as of December 31, 2021 and continued to be a stockholder as of December 31, 2022. $8,080 and $13,620 has been recognized as related party revenue as the Company has performed services under the Collaboration Agreement for the year ended December 31, 2022 and December 31, 2021, respectively. Further, the Company has made no payments to Ultragenyx during the years ended December 31, 2022 and 2021. There is $0 and $110 due from Ultragenyx as of December 31, 2022 and December 31, 2021, respectively. The amount received is deferred as a contract liability on the Company’s consolidated balance sheet as the performance obligation has been fully satisfied as of December 31, 2022.

The following table presents changes in the balances of the Company’s related party collaboration receivables and contract liabilities during the year ended December 31, 2022 and December 31, 2021, respectively:


	Balance as of December 31, 2021		Additions		Deductions			Balance as of December 31, 2022
Related party collaboration receivables	$	110	$	14	$	(124	)	$	—
Contract liabilities:
Deferred revenue		8,080		—		(8,080	)		—


	Balance as of December 31, 2020		Additions		Deductions			Balance as of December 31, 2021
Related party collaboration receivables	$	—	$	982	$	(872	)	$	110
Contract liabilities:
Deferred revenue		20,718		982		(13,620	)		8,080

The changes in the related party collaboration receivables balance during the year ended December 31, 2022 are the result of amounts owed to the Company for research and development services provided, offset by the collections received from Ultragenyx.

As of December 31, 2022 and December 31, 2021, there was $0 and $8,080, respectively, of deferred revenue related to the Collaboration Agreement, which is classified as either current or non-current in the accompanying consolidated balance sheet based on the period the services are expected to be delivered. Additionally, as of December 31, 2022 and December 31, 2021, there was $0 and $110, respectively, of related party collaboration receivables related to reimbursable costs expected to be received from Ultragenyx for research and development services performed.

Costs incurred relating to the Collaboration Agreement consist of internal and external research and development costs, which primarily include salaries and benefits, lab supplies, preclinical research studies, clinical studies, consulting services, and commercial development. These costs are included in research and development expenses in the Company’s consolidated statement of operations during the years ended December 31, 2022 and 2021.

Acquisition

12 Months Ended

Dec. 31, 2022

Business Combinations [Abstract]

Acquisition

4. Acquisition

On September 29, 2022, the Company entered into an Agreement and Plan of Merger with AavantiBio. The Acquisition closed on December 2, 2022 and was announced on December 5, 2022. This acquisition allows the Company to add to its pipeline of assets. The Company acquired AavantiBio for a total purchase price of $9,169, including (i) $1 in cash and (ii) 1,354,258 shares of its common stock, par value $0.001 per share with a fair value of $9,168 to AavantiBio equityholders. The price per share of the Company’s common stock used in the calculation of the purchase price is based on the closing price of Solid’s common stock on the Nasdaq Global Select Market on December 2, 2022, which was $6.77.

The Acquisition was accounted for as a business combination in which the Company, as the accounting acquirer, recorded the assets acquired and liabilities assumed from AavantiBio at their fair values as of the acquisition date. The Company recognized a gain on the purchase of AavantiBio of $18,236 as the net assets acquired of $27,405 were greater than the purchase price of $9,169. Prior to recognizing the gain, the Company reassessed the measurement and recognition of identifiable assets acquired, and liabilities assumed and concluded that the valuation procedures and resulting measures were appropriate, in all material respects. The Company believes that its ability to negotiate a purchase price lower than the fair market value of the acquired net assets was due to a combination of factors, including the then prevailing market conditions and the uncertain future macroeconomic environment. The Company believes the seller, as a smaller, less well capitalized company, was motivated to complete the transaction under the terms described above as growing economic uncertainty and a rising interest rate environment negatively impacted their ability to raise additional capital.

The Company incurred acquisition related costs of $4,870, which are included in general and administrative expenses in the Company’s consolidated statements of comprehensive loss for the fiscal year ended December 31, 2022.

The fair value is determined utilizing the fair value hierarchy as described in Note 2, Summary of Significant Accounting Policies, and Note 5, Fair Value of Financial Assets and Liabilities.

The following table summarizes the fair values of the assets acquired and liabilities assumed from AavantiBio at the acquisition date.


	December 2, 2022
Assets
Current assets:
Cash and cash equivalents	$	31,524
Prepaid expenses and other current assets		403
Total current assets		31,927
Operating lease, right-of-use asset		1,027
Property and equipment		2,765
Other non-current assets		23
Total assets	$	35,742
Liabilities
Current liabilities:
Accounts payable	$	3,575
Accrued expenses		3,634
Operating lease liabilities		778
Total current liabilities		7,987
Operating lease liabilities, excluding current portion		350
Total liabilities		8,337
Net assets acquired		27,405
Total consideration paid		9,169
Gain on acquisition of business	$	18,236

For the period from December 3, 2022 to December 31, 2022, AavantiBio's revenue and net loss before taxes included within the consolidated statement of operations subsequent to the closing of the acquisition was $0 and $6,041, respectively.

The following selected unaudited pro forma consolidated results of operations are presented as if the AavantiBio acquisition had occurred as of the beginning of the period immediately preceding the period of acquisition, which is January 1, 2021, after giving effect to certain adjustments. For fiscal year 2022, these adjustments included gain on the purchase of AavantiBio of $18,236 and one time transaction costs of $4,870 being removed. For fiscal year 2021, these adjustments included gain on the purchase of AavantiBio and one time transaction costs.


	Year Ended December 31,
		2022				2021
Revenues	$		8,094		$		13,620
Net income	$		(140,825	)	$		(95,417	)

Fair Value of Financial Assets and Liabilities

12 Months Ended

Dec. 31, 2022

Fair Value Disclosures [Abstract]

Fair Value of Financial Assets and Liabilities

5. Fair Value of Financial Assets and Liabilities

The following tables present information about the Company’s assets and liabilities that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values:


	Fair Value Measurements as of December 31, 2022:
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents	$	—	$	69,374	$	—	$	69,374
Available-for-sale securities		—		58,338		—		58,338
	$	—	$	127,712	$	—	$	127,712


	Fair Value Measurements as of December 31, 2021:
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents	$	—	$	75,224	$	—	$	75,224
Available-for-sale securities		—		88,643		—		88,643
	$	—	$	163,867	$	—	$	163,867

As of December 31, 2022 and December 31, 2021 the fair values of the Company’s cash equivalents and available-for-sale securities were determined using Level 2 inputs. During the year ended December 31, 2022 and December 31, 2021, there were no transfers between Level 1, Level 2 and Level 3, respectively.

The fair value of the Company’s cash, restricted cash, accounts payable, accrued expenses and other current liabilities approximate their carrying value due to their short-term maturities.

Available-for-Sale Securities

12 Months Ended

Dec. 31, 2022

Investments, Debt and Equity Securities [Abstract]

Available-for-Sale Securities

6. Available-for-Sale Securities

As of December 31, 2022, the fair value of available-for-sale debt securities by type of security was as follows:


	December 31, 2022
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Treasury bills	$	34,780	$	—	$	(30	)	$	34,750
Corporate bond securities		23,626		—		(38	)		23,588
	$	58,406	$	—	$	(68	)	$	58,338

As of December 31, 2021, the fair value of available-for-sale debt securities by type of security was as follows:


	December 31, 2021
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Treasury bill	$	2,800	$	—	$	—		$	2,800
Corporate bond securities		83,889		—		(45	)		83,844
Commercial paper		1,999		—		—			1,999
	$	88,688	$	—	$	(45	)	$	88,643

The estimated fair value and amortized cost of the Company’s available-for-sale securities by contractual maturity are summarized as follows:


	December 31, 2022
	Amortized Cost		Fair Value
Due in one year or less	$	58,406	$	58,338
Total available-for-sale securities	$	58,406	$	58,338


	December 31, 2021
	Amortized Cost		Fair Value
Due in one year or less	$	88,688	$	88,643
Total available-for-sale securities	$	88,688	$	88,643

The average maturity of the Company’s available-for-sale securities as of December 31, 2022 and December 31, 2021 was approximately 0.5 years and 0.7 years, respectively.

Prepaid Expenses and Other Current Assets

12 Months Ended

Dec. 31, 2022

Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]

Prepaid Expenses and Other Current Assets

7. Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consist of the following:


	December 31,
	2022		2021
Prepaid research and development expenses	$	2,913	$	6,015
Prepaid expenses and other assets		3,003		8,708
	$	5,916	$	14,723

Property and Equipment

12 Months Ended

Dec. 31, 2022

Property, Plant and Equipment [Abstract]

Property and Equipment

8. Property and Equipment

Property and equipment consists of the following:


	December 31,
	2022		2021
Furniture and fixtures	$	868	$	212
Laboratory equipment		16,416		10,719
Leasehold improvements		384		4,713
Computer equipment		677		436
Computer software		553		553
Construction in process		1,715		1,490
		20,613		18,123
Less accumulated depreciation		10,956		11,661
	$	9,657	$	6,462

Depreciation expense was $2,408, $2,964 and $3,922 for the years ended December 31, 2022, 2021 and 2020, respectively.

Accrued Expenses

12 Months Ended

Dec. 31, 2022

Payables and Accruals [Abstract]

Accrued Expenses

9. Accrued Expenses

Accrued expenses and other current liabilities consist of the following:


	December 31,
	2022		2021
Accrued research and development	$	3,033	$	1,507
Accrued compensation		8,370		3,084
Accrued other		5,288		4,937
	$	16,691	$	9,528

Equity-Based Compensation

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Equity-Based Compensation

10. Equity-Based Compensation

Equity Incentive Plans

In connection with the closing of the Company’s initial public offering, the Company's Board of Directors and stockholders approved the 2018 Omnibus Incentive Plan (the “2018 Plan”), which provides for the reservation of 333,400 shares of common stock for equity awards. On June 16, 2020, the Company’s stockholders approved the 2020 Equity Incentive Plan (as amended or restated, the “2020 Plan”) which consisted of, at the time of approval, (i) 200,000 shares of common stock and (ii) additional shares of common stock (up to 325,268) as is equal to (i) the number of shares reserved under the 2018 Plan that remain available for grant under the 2018 Plan as of immediately prior to the date the 2020 Plan was approved by the Company’s stockholders and (ii) the number of shares subject to awards granted under the 2018 Plan which awards expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right.

As of the effective date of the 2020 Plan, no further awards will be made under the 2018 Plan. Any options or awards outstanding under the 2018 Plan remain outstanding and effective and are governed by their existing terms.

On June 16, 2021, the Company’s stockholders approved an amendment to the 2020 Plan to reserve an additional 466,666 shares of common stock for issuance under the plan.

On December 1, 2022, the Company’s stockholders approved an amendment and restatement of the 2020 Plan to (i) increase the number of shares of common stock reserved for issuance under the plan by 866,666 shares to 1,533,333 shares, subject to adjustment in the event of stock splits and other similar events, (ii) provide for an annual increase, to be added on the first day of each fiscal year during the term of the plan, beginning with the fiscal year ending December 31, 2023, of 5% of the number of shares of common stock outstanding on the first day of such fiscal year or a lesser number of shares determined by the Company’s Board of Directors, (iii) provide that up to 1,858,601 shares of common stock may be granted as “incentive stock options” under the plan, (iv) extend the term of the plan to December 1, 2032 and (v) revise certain provisions of the plan relating to the Company’s Board of Directors’ ability to delegate authority to make awards under the plan.

At December 31, 2022, 1,049,472 shares remained available for future issuance under the 2020 Plan. Under the 2020 Plan, stock options may not be granted at less than fair value on the date of grant.

2021 Employee Stock Purchase Plan

The 2021 Employee Stock Purchase Plan (the “2021 ESPP”) was adopted by the Company's Board of Directors on April 14, 2021, approved by the stockholders on June 16, 2021, and became effective on June 16, 2021. The first offering period under the ESPP commenced on September 1, 2021. The number of shares of the Company’s common stock reserved for issuance under the 2021 ESPP is 73,525 shares. At December 31, 2022, 41,417 shares remained available for future issuance under the 2021 ESPP.

Stock Options

The following table summarizes the Company’s stock option activity for the year ended December 31, 2022:


	Number of Options			Weighted Average Exercise Price		Remaining Contractual Life (in years)
Outstanding at December 31, 2021		400,842		$	138.45		8.49
Granted		1,189,663			8.63
Exercised		—			—
Expired		(36,531	)		203.11
Forfeitures		(120,006	)		53.16
Outstanding at December 31, 2022		1,433,968			36.22		8.88
Vested and expected to vest as of December 31, 2022		1,433,968		$	36.22		8.88
Exercisable at December 31, 2022		195,104		$	163.79		7.00

At December 31, 2022, the Company had an aggregate of $12,708 of unrecognized equity-based compensation cost related to stock options outstanding which is expected to be recognized over a weighted average period of 3.19 years. The intrinsic value of stock options outstanding as of December 31, 2022 and 2021 was $0. The intrinsic value of stock options exercisable as of December 31, 2022 was $0. No stock options were exercised during the year ended December 31, 2022.

The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model using the assumptions noted in the following table for the years ended December 31:



	2022	2021	2020
Expected volatility	118.5 - 130.3%	115.5% - 123.9%	21.3% - 119.5%
Expected dividends	0.0%	0.0%	0.0%
Expected term (in years)	5.31-6.25	5.1 - 6.25	4.50 - 10.00
Risk-free rate	1.4 - 3.9%	0.4% - 1.4%	0.6% - 3.4%

The weighted average fair value of options to purchase shares of common stock granted during the year ended December 31, 2022 and 2021 was $7.59 and $75.75, respectively.

Restricted Stock Units

In 2022, 2021 and 2020, the Company's Board of Directors issued restricted stock units to employees. Restricted stock unit grants typically vest over one or two years.

The following table summarizes the Company’s restricted stock unit activity for the year ended December 31, 2022:


	Units			Weighted- Average Grant Date Fair Value
Unvested at December 31, 2021		33,980		$	41.29
Granted		556,179			8.93
Vested		(35,149	)		35.45
Forfeitures		(42,453	)		19.45
Outstanding at December 31, 2022		512,557		$	8.39
Unvested as of December 31, 2022		512,557		$	8.39

At December 31, 2022, the Company had an aggregate of $3,800 of unrecognized equity-based compensation cost related to restricted stock units outstanding. The unrecognized expense for the restricted stock units is expected to be recognized over a weighted average period of 3.5 years.

Restricted Common Stock

In connection with the Company’s Corporate Conversion on January 25, 2018, all restricted Series B and D common units were converted to restricted shares of common stock. As of December 31, 2021, there were no remaining restricted shares.

The aggregate intrinsic value of restricted common units that vested during the years ended December 31, 2022, 2021, and 2020 were $0, $199, and $522, respectively.

At December 31, 2022, the Company had an aggregate of $0 of unrecognized equity-based compensation related restricted shares of common stock.

The Company recorded equity-based compensation expense related to all of its share-based awards to employees and non-employees in the following captions within its consolidated statements of operations for the years ended December 31, 2022, 2021, and 2020:


	For the Year Ended December 31,
	2022		2021		2020
Research and development expenses	$	2,756	$	6,289	$	5,822
General and administrative expenses		4,781		7,084		4,956
Restructuring expenses		—		—		851
	$	7,537	$	13,373	$	11,629

Leases

12 Months Ended

Dec. 31, 2022

Leases [Abstract]

Leases

11. Leases

The Company has operating leases for laboratory and office space in Massachusetts, North Carolina and Florida.

In January 2019, the Company executed a lease agreement for additional office space in Cambridge, Massachusetts. The space serves as office space supporting the Company’s lab operations and consists of approximately 5,000 square feet. The term of the lease runs through October 2025. In June 2021, the Company determined that it no longer needed a floor of office space that it was renting and terminated its lease with another landlord. As a result of the termination, the Company wrote off $1,314 and $1,233 of the remaining lease liability and right-of-use asset, respectively, associated with the lease during the year ended December 31, 2021.

In June 2021, the Company entered into a lease with Hood Park LLC (“Landlord”), pursuant to which the Company leases approximately 49,869 square feet of office, laboratory, research and development and manufacturing space located in Charlestown, Massachusetts (“Premises”). The Company relocated its corporate headquarters to the Premises in June 2022. The initial term of the lease commenced in June 2022 when the construction of the lessor assets was substantially completed and continues for a ten-year period, unless earlier terminated. The lease provides the Company with an option to extend the lease for an additional five-year term. The Company and the Landlord were each obligated to undertake certain improvements prior to the commencement of the lease, and significant improvements were completed as of June 2022. The monthly lease payment is approximately $305 with annual escalation of approximately 3%. The lease includes a $10,223 construction allowance which is considered a lease incentive and included within the right-of-use asset. The Company was required to post a customary letter of credit in the amount of $1,833, subject to decrease on a set schedule, as a security deposit pursuant to the lease.

During the year ended December 31, 2022, the Company recorded a failed sales-leaseback transaction related to certain lab equipment. The related financing liabilities are recorded on the Company's consolidated balance sheets within financing labilities. In connection with this transaction, the Company also recorded a cash inflow within the financing activities under proceeds from financing liabilities of $2,143.

As of December 31, 2022, minimum future lease payments for these operating and finance leases were as follows:


	Finance Leases		Operating Leases
2023	$	1,109	$	4,574
2024		810		4,195
2025		651		4,092
2026		—		4,118
Thereafter		—		25,721
Total		2,570		42,700
Less: Imputed Interest		199		16,524
Total Lease Liabilities	$	2,371	$	26,176

The Company recorded rent expense of $3,881, $2,568 and $2,562 for the years ended December 31, 2022, 2021, and 2020, respectively.

Short-term lease and variable lease costs were not material for the year ended December 31, 2022 and 2021.

The supplemental disclosure of cash flow information related to the Company’s leases and the weighted average remaining lease term and weighted average discount rate of the Company’s leases are as follows:


	For the Year Ended December 31,			For the Year Ended December 31,			For the Year Ended December 31,
	2022			2021			2020
Other information
Cash paid for amounts included in the measurement of lease liabilities	$	2,840		$	2,408		$	2,408
Operating lease liabilities arising from obtaining right-of-use-assets	$	29,126		$	310		$	1,629
Finance lease liabilities arising from obtaining right-of-use assets	$	—		$	—		$	—
Weighted-average remaining lease term (in years)
Operating lease		9.3			1.0			2.8
Finance lease		2.5			2.3			2.3
Weighted-average discount rate
Operating lease		10.6	%		11.9	%		12.6	%
Finance lease		21.3	%		10.7	%		10.7	%

Commitments and Contingencies

12 Months Ended

Dec. 31, 2022

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

12. Commitments and Contingencies

Letter of Credit

The Company had outstanding letters of credit in the amounts of $1,833 and $2,070 at December 31, 2022 and 2021, respectively, which were required as a condition of the Company’s office and laboratory leases.

Indemnification Agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters, including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with its executive officers and members of its Board of Directors that require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as executive officers or directors. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnification arrangements.

The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its consolidated financial statements as of December 31, 2022 and 2021.

Legal Proceedings

The Company may periodically become subject to legal proceedings and claims arising in connection with ongoing business activities, including claims or disputes related to patents that have been issued or that are pending in the field of research on which the Company is focused. The Company is not aware of any material legal proceedings or claims as of December 31, 2022.

License Agreements

12 Months Ended

Dec. 31, 2022

Organization, Consolidation and Presentation of Financial Statements [Abstract]

License Agreements

13. License Agreements

University of Washington License Agreement

In 2015, the Company entered into a license agreement with the University of Washington, acting through UW CoMotion, under which the Company obtained an exclusive, royalty-bearing, sublicensable, worldwide license under a patent application owned by the University of Washington relating to novel micro-dystrophins and all patents claiming priority to such patent to develop, manufacture, and commercialize products for use in the treatment of Duchenne and related disease indications caused by a lack of functional dystrophin. The Company has the right to grant sublicenses to third parties contingent upon written approval by the University of Washington prior to executing such sublicense, which approval may not be unreasonably withheld.

In consideration for the rights granted by the agreement, the Company paid a one-time, non-refundable license fee, which was recorded as a research and development expense in 2015. The Company is required to reimburse the University of Washington for costs incurred in applying for, prosecuting and maintaining patents and pay up to an aggregate of approximately $1,000 upon the achievement of certain milestones. In October 2017, the first milestone was achieved under this agreement. The milestone payment was recorded as a research and development expense in the fourth quarter of 2017. In October 2020, the license agreement was amended such that the Company was required to pay the University of Washington $375 in connection with the execution of the Collaboration Agreement. This payment was recorded as a research and development expense in the fourth quarter of 2020. The license agreement was also amended such that the Company is required to pay an aggregate of approximately $3,400 upon the achievement of certain milestones. There were no milestones achieved during the years ended December 31, 2022, 2021, and 2020. The Company must also pay royalties of a low single digit percentage of future sales by the Company and its sublicensees of products developed under the licensed patent rights. In addition, the Company must pay an annual maintenance fee until certain milestones are achieved, at which time a minimum annual royalty requirement will replace such maintenance fee and will apply to the Company and its sublicensees.

The license agreement remains in effect until the expiration of the last-to-expire patent licensed under the agreement. The Company may terminate the agreement at any time upon providing sixty days’ written notice to the University of Washington. The University of Washington may terminate the agreement upon the Company’s uncured, material breach of the agreement or if the Company enters into an insolvency-related event.

The Company recorded research and development expense in the amount of $96, $60, and $446 for the years ended December 31, 2022, 2021, and 2020, respectively, under the agreement.

The University of Missouri License Agreement

In 2015, the Company entered into a license agreement with the Curators of the University of Missouri (the “University of Missouri”), a public corporation of Missouri, under which the Company obtained an exclusive, royalty-bearing, sublicensable, worldwide license under certain patent and patent applications owned by the University of Missouri relating to a novel synthetic microdystrophin gene to make, sell and distribute products for use in the treatment of Duchene and related disease indications resulting from a lack of functional dystrophin.

Under the agreement, in the event the Company grants a sublicenses to another party, the Company is required to pay the University of Missouri a percentage of the consideration received. The license agreement was amended such that the Company was required to pay the University of Missouri $750 in 2021 and $1,300 in 2022 as a result of the execution of the Collaboration Agreement with Ultragenyx in October 2020. These amounts were recorded as a research and development expense in the fourth quarter of 2020. The Company paid $750 in February 2021 and $1,300 in February 2022. The license agreement was also amended such that the Company is required to pay an aggregate of approximately $1,900 upon the achievement of certain milestones.

There were no milestones achieved during the years ended December 31, 2022, 2021, and 2020. The Company must pay a royalty of a low single digit percentage of future sales or by its sublicensees of products developed using the licensed patents. In addition, the Company must pay an annual maintenance fee until certain milestones are achieved, after which time a minimum annual royalty will replace such maintenance fee.

Under the agreement, the Company granted the University of Missouri a non-exclusive, royalty-free, irrevocable, paid-up license, with the right to grant sublicenses to non-profit, academic, educational or governmental institutions, to practice and use improvements made by the Company using the licensed patent rights, solely for non-commercial research purposes.

The license agreement remains in effect until the expiration of the last-to-expire patent or the abandonment of the last to be abandoned patent application licensed under the agreement. The University of Missouri may terminate the agreement, or render the license granted thereunder non-exclusive, in individual countries if the Company’s sublicensees fail to achieve certain milestones. The Company may terminate the license agreement at any time upon providing six months’ written notice to the University of Missouri and paying a termination fee. Each of the University of Missouri and the Company may also terminate the agreement for an uncured default or breach of the agreement by the other party. The Company’s ability to cure such breach only applies to the first two notices of such breach provided by the University of Missouri, and thereafter, the University of Missouri may terminate the agreement for the Company’s default or breach of the agreement upon thirty days’ written notice without an opportunity to cure such default or breach.

The Company recorded research and development expense in the amount of $133, $195, and $2,111 for the years ended December 31, 2022, 2021, and 2020, respectively, under the agreement.

The University of Michigan License Agreement

In 2016, the Company entered into a license agreement with the Regents of the University of Michigan, (the “University of Michigan”), a constitutional corporation of Michigan, under which the Company obtained an exclusive, royalty-bearing, sublicensable, worldwide license to make, sell and distribute products under certain patents owned by the University of Michigan related to microdystrophin and utrophin spectrin-like nucleic acid sequences for any use that, but for this agreement, would comprise an infringement of a valid claim included in the licensed patent rights.

In consideration for the rights granted by the agreement, the Company paid a one-time license fee and a separate fee to cover past patent prosecution costs, which the Company recorded as a research and development expense in 2016. The Company was required to reimburse the University of Michigan for costs incurred in applying for, prosecuting and maintaining patents, and pay up to an aggregate of approximately $1,000 upon the achievement of certain milestones. There were no milestones achieved during the years ended December 31, 2022, 2021, and 2020. The Company was also required to pay a royalty of a low single digit percentage on future sales by the Company or its sublicensees of products developed using the licensed rights, with a minimum annual royalty after certain milestones are achieved. In addition, the Company was required to pay an annual maintenance fee in any year in which the minimum annual royalty is not reached.

Under the agreement, the University of Michigan reserved for itself and its affiliates the right to use the licensed rights for non-commercial research, public service, internal and educational purposes and the right to grant the same limited non-commercial rights to other non-profit research institutions.

The Company recorded and research and development expense in the amount of $0, $37 and $35 for the years ended December 31, 2022, 2021, and 2020, respectively, under the agreement.

University of Florida License Agreements

In 2020, as amended, AavantiBio entered into license agreements with the University of Florida Research Foundation, Inc. (“UFRF”). Broadly, the agreements relate to FA. The Company acquired the agreements in connection with the Acquisition. Under each agreement the Company obtained an exclusive, royalty-bearing, sublicensable, world-wide license to certain patents and patent applications and a royalty-bearing non-exclusive license under the know-how, to make, have made, use, see, have sold, import and export licensed products. UFRF retains the right to practice the patent rights and know-how for internal non-commercial research, including research sponsored by commercial entities, and educational purposes.

In consideration for the rights granted under each agreement, AavantiBio paid a one-time non-refundable license fee. In connection with each agreement, the Company is required to pay an annual license maintenance fee until the first commercial sale of a licensed product after which time a minimum annual royalty will replace such maintenance fees. Under each agreement, the Company is required to reimburse UFRF for costs incurred in applying for, prosecuting and maintaining patents, pay up to an aggregate of approximately $2,900 upon the achievement of certain intellectual property, clinical and regulatory milestones for each licensed product under the agreement, and pay a low, single digit royalty on annual net sales by us and our sublicensees of licensed products on a licensed-product-by-licensed product basis. For any licensed product covered by both of these agreements, the Company is only obligated to make one payment for each milestone achieved and royalty payment due. Prior to the Acquisition, AavantiBio paid a single milestone fee related to the agreements of $50. Under each agreement, in the event the Company grants a sublicense to another party, the Company is required to pay UFRF a percentage of the consideration received.

Under each agreement, the Company has the right to grant sublicenses to third parties through multiple tiers, to the extent we are in compliance with our diligence obligations under the agreement and that sublicensee is subject to the terms of such agreement.

Under each agreement, the Company is obligated to use commercially reasonable efforts to develop and commercialize products covered by the licensed patent rights or know-how and to achieve certain regulatory and commercialization milestones within estimated time periods.

Under each agreement, UFRF controls the prosecution and maintenance of the licensed patents in consultation with the Company and at the Company's expense. In countries in which the Company has not requested prosecution or maintenance of licensed patents in a particular country or jurisdiction, the license granted to such patent rights will terminate in such country or jurisdiction. The Company has the first right to enforce such licensed patents at our expense.

Each of the agreements terminates on a licensed product-by-licensed product basis on the later of: (i) expiration of the patent rights covering such licensed product or (ii) ten (10) years from the first commercial sale of such licensed product. After five years, the Company may terminate an agreement for any reason giving advance written notice and reason for termination. UFRF may terminate an agreement for our uncured default or breach of the agreement. UFRF may immediately terminate an agreement if we bring or assist others in bringing a patent challenge against of the licensed patent rights. If UFRF sends the Company a written demand to terminate a sublicense agreement due to such sublicensee bringing or assisting a patent challenge, UFRF may terminate such agreement if we do not terminate the license with such sublicensee.

Net Loss per Share

12 Months Ended

Dec. 31, 2022

Earnings Per Share [Abstract]

Net Loss per Share

14. Net Loss per Share

Basic and diluted net loss per share were calculated as follows:

The numerator for basic and diluted net loss per share is as follows:


	For the Year Ended December 31,
	2022			2021			2020
Net loss	$	(85,981	)	$	(72,188	)	$	(88,290	)

The denominator is as follows:


	For the Year Ended December 31,
	2022		2021		2020
Weighted average common stock outstanding, basic and diluted		8,512,089		6,974,136		3,311,706
Weighted average pre-funded warrants to purchase common stock		—		143,888		150,769
Total		8,512,089		7,118,024		3,462,475

Net loss per share, basic and diluted is as follows:


	For the Year Ended December 31,
	2022			2021			2020
Net loss per share, basic and diluted	$	(10.10	)	$	(10.14	)	$	(25.50	)

The following potential common stock equivalents, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect:


	For the Year Ended December 31,
	2022		2021		2020
Options to purchase shares of common stock		1,433,968		400,842		207,851
Unvested restricted stock units		512,557		33,979		61,226
Unvested shares of common stock		—		—		4,670
		1,946,525		434,821		273,747

Income Taxes

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Income Taxes

15. Income Taxes

The Company recorded no tax benefit for the years ended December 31, 2022 and 2021 for the net operating losses incurred due to its uncertainty of realizing a benefit from those items.

A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations as of December 31, 2022 and 2021 is as follows:


	December 31, 2022			December 31, 2021
Income tax computed at federal statutory tax rate		21.0	%		21.0	%
State taxes, net of federal benefit		7.4	%		6.4	%
Permanent differences		(1.4	)%		0.5	%
Bargain purchase gain		4.5	%		—
Tax credits		11.5	%		12.1	%
Change in deferred tax rate		0.1	%		0.3	%
Stock compensation cancelations		(1.9	)%		(1.9	)%
Other		(0.6	)%		0.1	%
Valuation allowance		(40.6	)%		(38.5	)%
		0.0	%		0.0	%

The Company established deferred tax assets and liabilities on identified book to tax temporary differences as of the date of conversion to a C-corporation. Deferred income taxes reflect the net tax effects of these temporary differences between the

carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company’s net deferred tax assets as of December 31, 2022 and 2021 are as follows:


	December 31, 2022			December 31, 2021
Deferred tax assets:
Tax loss carryforwards	$	70,965		$	60,405
Tax credit carryforwards		46,786			36,905
Deferred expenses		7,174			420
Accrued expenses		1,901			815
Stock compensation		7,839			7,821
Intangible assets		36,553			19,919
Depreciation		116			224
Other		166			2,373
Total deferred tax assets		171,500			128,882
Valuation allowance		(163,566	)		(128,570	)
Deferred tax liabilities:
Right-of-use asset		(7,934	)		(312	)
Total deferred tax liabilities		(7,934	)		(312	)
Net deferred taxes	$	—		$	—

As of December 31, 2022, the Company has federal net operating loss carryforwards of $259,924 which may be available to offset future taxable income and do not expire, but are limited in their usage to an annual deduction equal to 80% of annual taxable income. In addition, as of December 31, 2022, the Company has state net operating loss carryforwards of approximately $259,342 which may be available to offset future taxable income, of which $258,152 begins to expire in 2038 and $1,190 has unlimited carryforward. The Company also had federal and state tax credits of $43,404 and $4,280, respectively, which may be used to offset future tax liability and each of which begin to expire in 2033.

The Company’s ability to utilize these federal and state carryforwards may be limited in the future if the Company experiences an ownership change pursuant to Internal Revenue Code Section 382. Ownership changes, as defined in the Internal Revenue Code, including those resulting from the issuance of common stock in connection with the Company’s public offerings, may limit the amount of net operating loss and tax credit carryforwards that can be utilized to offset future taxable income or tax liability. The Company has not completed a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the net operating loss carryforwards tax credit carryforwards would be subject to an annual limitation under Section 382. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before utilization. Further, until a study is completed and any limitation is known, no amounts are being presented as an uncertain tax position.

Section 382 also limits the Company’s ability to utilize the tax deductions associated with AavantiBio amortization and depreciation and AavantiBio’s net operating losses. As of December 31, 2022, the Company concluded that all of AavantiBio’s tax deductions associated with amortization and depreciation and AavantiBio’s net operating losses are more likely than not subject to restrictive limitation and will not be utilizable.

A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. The Company has evaluated the positive and negative evidence bearing upon the realizability of the deferred tax assets. The Company concluded, in accordance with the applicable accounting standards, that it is more likely than not that the Company will be unable to realize the benefit of its deferred tax assets. Accordingly, the Company has recorded a full valuation allowance against its deferred tax assets.

The following table presents the changes in the balance of the Company’s deferred income tax asset valuation allowance:


	December 31, 2022		December 31, 2021
Valuation allowance at beginning of year	$	128,570	$	100,740
Increases recorded to income tax provision		34,996		27,830
Valuation allowance at end of year	$	163,566	$	128,570

The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending income tax examinations. The Company’s C-Corporation tax years beginning with the year ended December 31,

2019 are open under statute. Any tax credit or net operating loss carryforward can be adjusted in future periods after the respective year of generation’s statute of limitation has closed.

As of December 31, 2022 and 2021, the Company did not have unrecognized tax benefits. The Company recognizes interest and penalties related to income taxes as a component of income tax expense. As of December 31, 2022 and 2021, no interest and penalties have been recorded.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 21
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32857-109319

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-URI https://asc.fasb.org/extlink&oid=122134291&loc=d3e330215-122817

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 17
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32809-109319

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-URI https://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 14
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32705-109319

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 270
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6424409&loc=d3e44925-109338

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-URI https://asc.fasb.org/topic&trid=2144680

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Defined Contribution Plan

12 Months Ended

Dec. 31, 2022

Retirement Benefits [Abstract]

Defined Contribution Plan

16. Defined Contribution Plan

The Company has a defined contribution savings plan under Section 401(k) of the Internal Revenue Code. The plan covers substantially all employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pretax basis. Company contributions to the plan may be made at the discretion of the Company’s Board of Directors. The Company made $527 and $241 of contributions during the years ended December 31, 2022 and December 31, 2021, respectively. The company had made no contributions to the plan during the years ended December 31, 2020.

Restructuring

12 Months Ended

Dec. 31, 2022

Restructuring and Related Activities [Abstract]

Restructuring

17. Restructuring

January 2020 Plan

In January 2020, the Company’s Board of Directors approved a restructuring plan to reduce operating costs and better align the Company’s workforce with the needs of its business following the Company’s November 2019 announcement that the SGT-001 IGNITE DMD trial was placed on clinical hold by the FDA.

Under the restructuring plan, the Company made changes to its management team and reduced headcount by approximately 30 percent. Affected employees were eligible to receive severance payments and outplacement services in connection with the restructuring plan. During year ended December 31, 2020, the Company recorded aggregate restructuring charges of $1,944 related to severance payments and other employee-related costs. The Company does not expect to incur any additional significant costs associated with this restructuring. During the year ended December 31, 2020, $1,882 of the estimated restructuring charges were paid.

April 2022 Plan

In April 2022, the Company implemented changes to its corporate strategy to prioritize the advancement of its then-key programs, SGT-001 and SGT-003. In connection with the changes to corporate operations, the Company reduced headcount by approximately 35 percent. During the year ended December 31, 2022, the Company recorded and paid aggregate restructuring charges of $1,520 related to severance and other employee related costs in connection with the changes to its corporate strategy. The Company does not expect to incur any additional significant costs associated with this restructuring.

November 2022 Plan

In November 2022, the Company’s Board of Directors approved a plan to reduce the Company’s workforce by approximately 18 percent. These reductions were completed by December 5, 2022. This plan was designed to streamline the Company’s operating structure following the Acquisition. The Company recorded a restructuring charge in the fourth quarter of 2022 of $5,658 related to the reduction in force, consisting of severance and other employee termination benefits. The Company paid $1,737 of this amount during the year ended December 31, 2022. The Company expects that approximately the remaining $3,921 will be paid by the first quarter of 2024.

The following table shows the total amount incurred and the liability related to the associated restructuring plans for the years ended December 31, 2022, 2021 and 2020:


One-Time Employee Termination Benefits	January 2020			April 2022			November 2022
Accrued restructuring costs as of December 31, 2020	$	62		$	—		$	—
Restructuring charges incurred during the period		—			—			—
Amounts paid during the period		(62	)		—			—
Accrued restructuring costs as of December 31, 2021	$	—		$	—		$	—
Restructuring charges incurred during the period		—			1,520			5,658
Amounts paid during the period		—			(1,520	)		(1,737	)
Accrued restructuring costs as of December 31, 2022	$	—		$	—		$	3,921

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2022

Accounting Policies [Abstract]

Use of Estimates

Cash Equivalents

The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents.

Restricted Cash


	December 31, 2022		December 31, 2021		December 31, 2020		December 31, 2019
Cash and cash equivalents	$	155,384	$	119,136	$	154,744	$	76,043
Restricted cash, non-current		1,833		2,070		327		327
Cash and cash equivalents and restricted cash	$	157,217	$	121,206	$	155,071	$	76,370

Available-for-Sale Securities

Concentration of Credit Risk and of Significant Suppliers

Fair Value Measurements

•

Level 1—Quoted prices in active markets for identical assets or liabilities.

•

Leases

Property and Equipment

Impairment of Long-Lived Assets

Revenue Recognition

Exclusive Licenses

Research and Development Services

Milestone Payments

Royalties

Collaboration Revenue

Costs Associated with License and Collaborative Arrangements

All costs associated with license and collaborative arrangements are expensed as incurred and recorded in research and development expense in the consolidated statements of operations.

Research and Development Costs

Research Contract Costs and Accruals

Patent Costs

Equity-Based Compensation

The fair value for restricted stock units (“RSU”) was calculated using the closing price of the Company’s common stock on the date of grant.

participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed.

Contingencies

Business Combinations

Recently Issued Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2022

Accounting Policies [Abstract]

Reconciliation of Amounts From Cash Flow Statement to Balance Sheet

A reconciliation of the amounts of cash and cash equivalents and restricted cash from the cash flow statement to the balance sheet is as follows:


	December 31, 2022		December 31, 2021		December 31, 2020		December 31, 2019
Cash and cash equivalents	$	155,384	$	119,136	$	154,744	$	76,043
Restricted cash, non-current		1,833		2,070		327		327
Cash and cash equivalents and restricted cash	$	157,217	$	121,206	$	155,071	$	76,370

Collaborations (Tables)

12 Months Ended

Dec. 31, 2022

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Summary of Changes in Balances of Company's Related Party Collaboration Receivables and Contract Liabilities


	Balance as of December 31, 2021		Additions		Deductions			Balance as of December 31, 2022
Related party collaboration receivables	$	110	$	14	$	(124	)	$	—
Contract liabilities:
Deferred revenue		8,080		—		(8,080	)		—


	Balance as of December 31, 2020		Additions		Deductions			Balance as of December 31, 2021
Related party collaboration receivables	$	—	$	982	$	(872	)	$	110
Contract liabilities:
Deferred revenue		20,718		982		(13,620	)		8,080

Acquisition (Tables)

12 Months Ended

Dec. 31, 2022

Business Combinations [Abstract]

Summary of Fair Values of Assets Acquired and Liabilities Assumed

The following table summarizes the fair values of the assets acquired and liabilities assumed from AavantiBio at the acquisition date.


	December 2, 2022
Assets
Current assets:
Cash and cash equivalents	$	31,524
Prepaid expenses and other current assets		403
Total current assets		31,927
Operating lease, right-of-use asset		1,027
Property and equipment		2,765
Other non-current assets		23
Total assets	$	35,742
Liabilities
Current liabilities:
Accounts payable	$	3,575
Accrued expenses		3,634
Operating lease liabilities		778
Total current liabilities		7,987
Operating lease liabilities, excluding current portion		350
Total liabilities		8,337
Net assets acquired		27,405
Total consideration paid		9,169
Gain on acquisition of business	$	18,236

Summary of Unaudited Proforma Information


	Year Ended December 31,
		2022				2021
Revenues	$		8,094		$		13,620
Net income	$		(140,825	)	$		(95,417	)

Fair Value of Financial Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2022

Fair Value Disclosures [Abstract]

Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis and Indicate Level of Fair Value Hierarchy Utilized


	Fair Value Measurements as of December 31, 2022:
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents	$	—	$	69,374	$	—	$	69,374
Available-for-sale securities		—		58,338		—		58,338
	$	—	$	127,712	$	—	$	127,712


	Fair Value Measurements as of December 31, 2021:
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents	$	—	$	75,224	$	—	$	75,224
Available-for-sale securities		—		88,643		—		88,643
	$	—	$	163,867	$	—	$	163,867

Available-for-Sale Securities (Tables)

12 Months Ended

Dec. 31, 2022

Investments, Debt and Equity Securities [Abstract]

Schedule of Fair Value of Available-for-Sale Debt Securities by Type of Security

As of December 31, 2022, the fair value of available-for-sale debt securities by type of security was as follows:


	December 31, 2022
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Treasury bills	$	34,780	$	—	$	(30	)	$	34,750
Corporate bond securities		23,626		—		(38	)		23,588
	$	58,406	$	—	$	(68	)	$	58,338

As of December 31, 2021, the fair value of available-for-sale debt securities by type of security was as follows:


	December 31, 2021
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Treasury bill	$	2,800	$	—	$	—		$	2,800
Corporate bond securities		83,889		—		(45	)		83,844
Commercial paper		1,999		—		—			1,999
	$	88,688	$	—	$	(45	)	$	88,643

Summary Estimated Fair Value and Amortized Cost of Available-for-Sale Securities by Contractual Maturity

The estimated fair value and amortized cost of the Company’s available-for-sale securities by contractual maturity are summarized as follows:


	December 31, 2022
	Amortized Cost		Fair Value
Due in one year or less	$	58,406	$	58,338
Total available-for-sale securities	$	58,406	$	58,338


	December 31, 2021
	Amortized Cost		Fair Value
Due in one year or less	$	88,688	$	88,643
Total available-for-sale securities	$	88,688	$	88,643

Prepaid Expenses and Other Current Assets (Tables)

12 Months Ended

Dec. 31, 2022

Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]

Schedule of Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consist of the following:


	December 31,
	2022		2021
Prepaid research and development expenses	$	2,913	$	6,015
Prepaid expenses and other assets		3,003		8,708
	$	5,916	$	14,723

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2022

Property, Plant and Equipment [Abstract]

Summary of Property and Equipment

Property and equipment consists of the following:


	December 31,
	2022		2021
Furniture and fixtures	$	868	$	212
Laboratory equipment		16,416		10,719
Leasehold improvements		384		4,713
Computer equipment		677		436
Computer software		553		553
Construction in process		1,715		1,490
		20,613		18,123
Less accumulated depreciation		10,956		11,661
	$	9,657	$	6,462

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2022

Payables and Accruals [Abstract]

Summary of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consist of the following:


	December 31,
	2022		2021
Accrued research and development	$	3,033	$	1,507
Accrued compensation		8,370		3,084
Accrued other		5,288		4,937
	$	16,691	$	9,528

Equity-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity for the year ended December 31, 2022:


	Number of Options			Weighted Average Exercise Price		Remaining Contractual Life (in years)
Outstanding at December 31, 2021		400,842		$	138.45		8.49
Granted		1,189,663			8.63
Exercised		—			—
Expired		(36,531	)		203.11
Forfeitures		(120,006	)		53.16
Outstanding at December 31, 2022		1,433,968			36.22		8.88
Vested and expected to vest as of December 31, 2022		1,433,968		$	36.22		8.88
Exercisable at December 31, 2022		195,104		$	163.79		7.00

Assumptions for Measuring Fair Values of Stock Options

The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model using the assumptions noted in the following table for the years ended December 31:



	2022	2021	2020
Expected volatility	118.5 - 130.3%	115.5% - 123.9%	21.3% - 119.5%
Expected dividends	0.0%	0.0%	0.0%
Expected term (in years)	5.31-6.25	5.1 - 6.25	4.50 - 10.00
Risk-free rate	1.4 - 3.9%	0.4% - 1.4%	0.6% - 3.4%

Summary of Restricted Stock Unit Activity

The following table summarizes the Company’s restricted stock unit activity for the year ended December 31, 2022:


	Units			Weighted- Average Grant Date Fair Value
Unvested at December 31, 2021		33,980		$	41.29
Granted		556,179			8.93
Vested		(35,149	)		35.45
Forfeitures		(42,453	)		19.45
Outstanding at December 31, 2022		512,557		$	8.39
Unvested as of December 31, 2022		512,557		$	8.39

Schedule of Equity-based Compensation Expense


	For the Year Ended December 31,
	2022		2021		2020
Research and development expenses	$	2,756	$	6,289	$	5,822
General and administrative expenses		4,781		7,084		4,956
Restructuring expenses		—		—		851
	$	7,537	$	13,373	$	11,629

Leases (Tables)

12 Months Ended

Dec. 31, 2022

Leases [Abstract]

Future Minimum Payments for Operating and Finance Leases

As of December 31, 2022, minimum future lease payments for these operating and finance leases were as follows:


	Finance Leases		Operating Leases
2023	$	1,109	$	4,574
2024		810		4,195
2025		651		4,092
2026		—		4,118
Thereafter		—		25,721
Total		2,570		42,700
Less: Imputed Interest		199		16,524
Total Lease Liabilities	$	2,371	$	26,176

Supplemental Disclosure of Cash Flow Information Related to Leases and Weighted Average Remaining Lease Term and Discount Rate


	For the Year Ended December 31,			For the Year Ended December 31,			For the Year Ended December 31,
	2022			2021			2020
Other information
Cash paid for amounts included in the measurement of lease liabilities	$	2,840		$	2,408		$	2,408
Operating lease liabilities arising from obtaining right-of-use-assets	$	29,126		$	310		$	1,629
Finance lease liabilities arising from obtaining right-of-use assets	$	—		$	—		$	—
Weighted-average remaining lease term (in years)
Operating lease		9.3			1.0			2.8
Finance lease		2.5			2.3			2.3
Weighted-average discount rate
Operating lease		10.6	%		11.9	%		12.6	%
Finance lease		21.3	%		10.7	%		10.7	%

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2022

Earnings Per Share [Abstract]

Schedule of Basic and Diluted Net Loss per Share

The numerator for basic and diluted net loss per share is as follows:


	For the Year Ended December 31,
	2022			2021			2020
Net loss	$	(85,981	)	$	(72,188	)	$	(88,290	)

The denominator is as follows:


	For the Year Ended December 31,
	2022		2021		2020
Weighted average common stock outstanding, basic and diluted		8,512,089		6,974,136		3,311,706
Weighted average pre-funded warrants to purchase common stock		—		143,888		150,769
Total		8,512,089		7,118,024		3,462,475

Net loss per share, basic and diluted is as follows:


	For the Year Ended December 31,
	2022			2021			2020
Net loss per share, basic and diluted	$	(10.10	)	$	(10.14	)	$	(25.50	)

Schedule of Antidilutive Securities Excluded from Calculation of Diluted Net Loss per Share


	For the Year Ended December 31,
	2022		2021		2020
Options to purchase shares of common stock		1,433,968		400,842		207,851
Unvested restricted stock units		512,557		33,979		61,226
Unvested shares of common stock		—		—		4,670
		1,946,525		434,821		273,747

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of Income Taxes Computed by U.S. Federal Statutory Rate

A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations as of December 31, 2022 and 2021 is as follows:


	December 31, 2022			December 31, 2021
Income tax computed at federal statutory tax rate		21.0	%		21.0	%
State taxes, net of federal benefit		7.4	%		6.4	%
Permanent differences		(1.4	)%		0.5	%
Bargain purchase gain		4.5	%		—
Tax credits		11.5	%		12.1	%
Change in deferred tax rate		0.1	%		0.3	%
Stock compensation cancelations		(1.9	)%		(1.9	)%
Other		(0.6	)%		0.1	%
Valuation allowance		(40.6	)%		(38.5	)%
		0.0	%		0.0	%

Schedule of Net Deferred Tax Assets

Significant components of the Company’s net deferred tax assets as of December 31, 2022 and 2021 are as follows:


	December 31, 2022			December 31, 2021
Deferred tax assets:
Tax loss carryforwards	$	70,965		$	60,405
Tax credit carryforwards		46,786			36,905
Deferred expenses		7,174			420
Accrued expenses		1,901			815
Stock compensation		7,839			7,821
Intangible assets		36,553			19,919
Depreciation		116			224
Other		166			2,373
Total deferred tax assets		171,500			128,882
Valuation allowance		(163,566	)		(128,570	)
Deferred tax liabilities:
Right-of-use asset		(7,934	)		(312	)
Total deferred tax liabilities		(7,934	)		(312	)
Net deferred taxes	$	—		$	—

Schedule of Deferred Income Tax Asset Valuation Allowance

The following table presents the changes in the balance of the Company’s deferred income tax asset valuation allowance:


	December 31, 2022		December 31, 2021
Valuation allowance at beginning of year	$	128,570	$	100,740
Increases recorded to income tax provision		34,996		27,830
Valuation allowance at end of year	$	163,566	$	128,570

Restructuring (Tables)

12 Months Ended

Dec. 31, 2022

Restructuring and Related Activities [Abstract]

Schedule of Total Amount Incurred and Liability Related to Associated Restructuring Plans

The following table shows the total amount incurred and the liability related to the associated restructuring plans for the years ended December 31, 2022, 2021 and 2020:


One-Time Employee Termination Benefits	January 2020			April 2022			November 2022
Accrued restructuring costs as of December 31, 2020	$	62		$	—		$	—
Restructuring charges incurred during the period		—			—			—
Amounts paid during the period		(62	)		—			—
Accrued restructuring costs as of December 31, 2021	$	—		$	—		$	—
Restructuring charges incurred during the period		—			1,520			5,658
Amounts paid during the period		—			(1,520	)		(1,737	)
Accrued restructuring costs as of December 31, 2022	$	—		$	—		$	3,921

Nature of the Business and Basis of Presentation - Additional Information (Detail) $ in Thousands			12 Months Ended
	Dec. 02, 2022 USD ($) shares	Oct. 27, 2022 shares	Dec. 31, 2022 USD ($) shares	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($) shares	Oct. 28, 2022 shares	Jun. 30, 2022 shares
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Net loss			$ 85,981	$ 72,188	$ 88,290
Accumulated deficit			562,738	476,757
Net cash used in operating activities			97,977	$ 77,764	$ 56,599
Cash, cash equivalents and available-for-sale securities			213,722
Restricted cash			$ 1,833
Stockholders' equity note, stock split, conversion ratio		0.067
Reverse stock split of outstanding shares of common stock		one-for-15
Common stock, shares authorized \| shares		20,000,000	60,000,000	20,000,000		60,000,000	300,000,000
Securities Purchase Agreement [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Net proceeds from private placement	$ 72,551
Common Stock [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Common stock shares issued \| shares			10,638,290	1,666,666	2,042,263
Common Stock [Member] \| Securities Purchase Agreement [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Common stock shares issued \| shares	10,638,290

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Nov. 30, 2020	Oct. 31, 2020	Dec. 31, 2019
Significant Accounting Policies [Line Items]
Restricted cash deposit	$ 1,833,000	$ 2,070,000
Restricted cash noncurrent	1,833,000	2,070,000	$ 327,000			$ 327,000
Income tax expense (benefit)	$ 0	$ 0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, shares issued	19,556,732	7,356,017
Payment of exchange fees	$ 1,965,000
Cost relating to consulting agreement	$ 1,472,000	$ 777,000
Common stock shares issued warrant to purchase				2,000
Common stock warrants exercise price per share				$ 49.35
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement [Member] \| Ultragenyx [Member]
Significant Accounting Policies [Line Items]
Common stock, shares issued					521,719
ASC Topic 606 [Member]
Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted	true
Laboratory Equipment [Member]
Significant Accounting Policies [Line Items]
Useful life of asset	5 years
Computer Equipment [Member]
Significant Accounting Policies [Line Items]
Useful life of asset	3 years
Computer Software [Member]
Significant Accounting Policies [Line Items]
Useful life of asset	2 years
Furniture and Office Equipment [Member]
Significant Accounting Policies [Line Items]
Useful life of asset	5 years
Leasehold Improvements [Member]
Significant Accounting Policies [Line Items]
Useful life of asset	shorter of the lease term or the estimated useful life of the related asset

Summary of Significant Accounting Policies - Reconciliation of Amounts From Cash Flow Statement to Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reconciliation Of Beginning And End Of Period Amounts From Cash Flow Statement To Balance Sheet [Abstract]
Cash and cash equivalents	$ 155,384	$ 119,136	$ 154,744	$ 76,043
Restricted Cash, Noncurrent	1,833	2,070	327	327
Cash and cash equivalents and restricted cash	$ 157,217	$ 121,206	$ 155,071	$ 76,370

Collaborations - Additional Information (Detail) - USD ($)		12 Months Ended
	Oct. 22, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from issuance of common stock, net of issuance costs		$ 72,551,000	$ 134,878,000	$ 113,208,000
Accounts receivable - related party			110,000
Ultragenyx [Member] \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments upon achievement of regulatory milestone		$ 65,000,000
Percentage of option to fund of development cost		30.00%
Percentage of net income and net losses on net sales		30.00%
Agreement termination notice period		90 days
Issued and sold shares of common stock	521,719
Common stock issued price per share	$ 76.6695
Proceeds from issuance of common stock, net of issuance costs	$ 40,000,000
Percentage of outstanding common stock	14.45%	2.70%
Transaction price determined under ASC 606		$ 22,513,000
Transaction price		0
Related party revenue recognized		8,080,000	13,620,000
Related party transaction, payment		0	0
Due from related parties		0	110,000
Deferred revenue		0	8,080,000	$ 20,718,000
Accounts receivable - related party		0	$ 110,000
Ultragenyx [Member] \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments upon achievement of development milestone		25,000,000
Milestone Payments upon achievement of net sales milestones		$ 165,000,000
Ultragenyx [Member] \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement [Member] \| Minimum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of outstanding common stock		10.00%

Collaborations - Summary of Changes in Balances of Company's Related Party Collaboration Receivables and Contract Liabilities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Related party collaboration receivables, Beginning balance	$ 110
Related party collaboration receivables, Ending balance		$ 110
Ultragenyx [Member] \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Related party collaboration receivables, Beginning balance	110
Related party collaboration receivables, Additions	14	982
Related party collaboration receivables, Deductions	(124)	(872)
Related party collaboration receivables, Ending balance	0	110
Deferred revenue, Beginning balance	8,080	20,718
Deferred revenue, Additions		982
Deferred revenue, Deductions	(8,080)	(13,620)
Deferred revenue, Ending balance	$ 0	$ 8,080

Acquisition - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	Dec. 02, 2022	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2021
Business Acquisition [Line Items]
Gain on acquisition			$ 18,236
AavantiBio, Inc [Member]
Business Acquisition [Line Items]
Business acquisition, effective date of acquisition	Sep. 29, 2022
Business acquisition, Acquisition completion date	Dec. 02, 2022
Total purchase price	$ 9,169
Cash payment	$ 1
Number of shares of common stock	1,354,258
Business acquisition, share price	$ 0.001
Business Acquisition, fair value	$ 9,168
Gain on acquisition	18,236		18,236
Acquisition related costs	4,870
Net assets acquired	$ 27,405
Revenues		$ 0	8,094	$ 13,620
One time transaction costs		4,870	$ 4,870
Net loss before taxes		$ 6,041
AavantiBio, Inc [Member] \| Common Stock [Member]
Business Acquisition [Line Items]
Business acquisition, share price	$ 6.77
AavantiBio, Inc [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Total purchase price	$ 9,169

Acquisition - Summary of Fair Values of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands		12 Months Ended
	Dec. 02, 2022	Dec. 31, 2022
Current liabilities:
Gain on acquisition of business		$ 18,236
AavantiBio, Inc [Member]
Current assets:
Cash and cash equivalents	$ 31,524
Prepaid expenses and other current assets	403
Total current assets	31,927
Operating lease, right-of-use asset	1,027
Property and equipment, net	2,765
Other non-current assets	23
Total assets	35,742
Current liabilities:
Accounts payable	3,575
Accrued expenses	3,634
Operating lease liabilities	778
Total current liabilities	7,987
Operating lease liabilities, excluding current portion	350
Total liabilities	8,337
Net assets acquired	27,405
Total consideration paid	9,169
Gain on acquisition of business	$ 18,236	$ 18,236

Acquisition - Summary of Unaudited Proforma Information (Detail) - AavantiBio, Inc [Member] - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2021
Business Acquisition [Line Items]
Revenues	$ 0	$ 8,094	$ 13,620
Net income		$ (140,825)	$ (95,417)

Fair Value of Financial Assets and Liabilities - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis and Indicate Level of Fair Value Hierarchy Utilized (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Assets:
Cash equivalents	$ 69,374	$ 75,224
Available-for-sale securities	58,338	88,643
Assets Fair Value Disclosure	127,712	163,867
Level 2 [Member]
Assets:
Cash equivalents	69,374	75,224
Available-for-sale securities	58,338	88,643
Assets Fair Value Disclosure	$ 127,712	$ 163,867

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Fair value, assets, transfers into level 3, amount	$ 0	$ 0
Fair value, assets, transfers out of level 3, amount	0	0
Fair value, assets, transfers into level 2, amount	0	0
Fair value, assets, transfers out of level 2, amount	0	0
Fair value, assets, transfers into level 1, amount	0	0
Fair value, assets, transfers out of level 1, amount	$ 0	$ 0

Available-for-Sale Securities - Schedule of Fair Value of Available-for-Sale Debt Securities by Type of Security (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 58,406	$ 88,688
Gross Unrealized Loss	(68)	(45)
Fair Value	58,338	88,643
Treasury Bills [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	34,780	2,800
Gross Unrealized Loss	(30)
Fair Value	34,750	2,800
Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	23,626	83,889
Gross Unrealized Loss	(38)	(45)
Fair Value	$ 23,588	83,844
Commercial Paper [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		1,999
Fair Value		$ 1,999

Available-for-Sale Securities - Summary Estimated Fair Value and Amortized Cost of Available-for-Sale Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, amortized cost	$ 58,406	$ 88,688
Amortized Cost	58,406	88,688
Due in one year or less, fair value	58,338	88,643
Total available-for-sale securities, fair value	$ 58,338	$ 88,643

Available-for-Sale Securities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities average maturity period	6 months	8 months 12 days

Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid research and development expenses	$ 2,913	$ 6,015
Prepaid expenses and other assets	3,003	8,708
Prepaid expenses and other current assets	$ 5,916	$ 14,723

Property and Equipment - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 20,613	$ 18,123
Less accumulated depreciation	10,956	11,661
Property and equipment, net	9,657	6,462
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	868	212
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	16,416	10,719
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	384	4,713
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	677	436
Computer Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	553	553
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,715	$ 1,490

Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 2,408	$ 2,964	$ 3,922

Accrued Expenses - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	$ 16,691	$ 9,528
Accrued Research and Development [Member]
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	3,033	1,507
Accrued Compensation [Member]
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	8,370	3,084
Accrued Other [Member]
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	$ 5,288	$ 4,937

Equity-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	12 Months Ended
	Dec. 31, 2022	Jun. 16, 2020	Jun. 30, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 01, 2022	Jun. 16, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options outstanding, weighted average recognition period				8 years 10 months 17 days	8 years 5 months 26 days
Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized equity-based compensation cost related to stock option	$ 12,708			$ 12,708
Stock options outstanding, weighted average recognition period	3 years 2 months 8 days
Stock options outstanding, intrinsic value	$ 0			0	$ 0
Intrinsic value of stock options exercisable	0			$ 0
Stock options exercised				0
Weighted average fair value of options to purchase common stock granted				$ 7.59	$ 75.75
'Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized equity-based compensation	3,800			$ 3,800
Unrecognized equity-based compensation cost, weighted average period				3 years 6 months
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized equity-based compensation	$ 0			$ 0
Aggregate intrinsic value of restricted common units vested				$ 0	$ 199	$ 522
Incentive Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for future issuance							1,858,601
Maximum [Member] \| 'Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				2 years
Minimum [Member] \| 'Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				1 year
2018 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for common stock for equity awards	333,400			333,400
2020 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for common stock for equity awards		200,000
Number of additional shares authorized for common stock for equity awards			466,666
Number of shares available for future issuance	1,049,472			1,049,472
2020 Equity Incentive Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of additional shares authorized for common stock for equity awards		325,268
2021 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for common stock for equity awards								73,525
Number of shares available for future issuance	41,417			41,417
Amended and Restated 2020 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of additional shares authorized for common stock for equity awards				866,666
Number of share reserved for future issuance							1,533,333
Percentage of number of shares outstanding				5.00%

Equity-Based Compensation - Summary of Stock Option Activity (Detail)	12 Months Ended
	Dec. 31, 2022 $ / shares shares	Dec. 31, 2021 $ / shares shares
Number of Options
Outstanding at December 31, 2021 \| shares	400,842
Granted \| shares	1,189,663
Expired \| shares	(36,531)
Forfeitures \| shares	(120,006)
Outstanding at December 31, 2022 \| shares	1,433,968	400,842
Vested and expected to vest as of December 31, 2022 \| shares	1,433,968
Exercisable at December 31, 2022 \| shares	195,104
Weighted Average Exercise Price
Outstanding at December 31, 2021 \| $ / shares	$ 138.45
Granted \| $ / shares	8.63
Expired \| $ / shares	203.11
Forfeitures \| $ / shares	53.16
Outstanding at December 31, 2022 \| $ / shares	36.22	$ 138.45
Vested and expected to vest as of December 31, 2022 \| $ / shares	36.22
Exercisable at December 31, 2022 \| $ / shares	$ 163.79
Remaining Contractual Life (in years)
Outstanding	8 years 10 months 17 days	8 years 5 months 26 days
Vested and expected to vest as of December 31, 2022	8 years 10 months 17 days
Exercisable at December 31, 2022	7 years

Equity-Based Compensation - Assumptions for Measuring Fair Values of Stock Options (Detail)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, Minimum	118.50%	115.50%	21.30%
Expected volatility, Maximum	130.30%	123.90%	119.50%
Expected dividends	0.00%	0.00%	0.00%
Risk-free rate, Minimum	1.40%	0.40%	0.60%
Risk-free rate, Maximum	3.90%	1.40%	3.40%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 3 months 21 days	5 years 1 month 6 days	4 years 6 months
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 3 months	6 years 3 months	10 years

Equity-Based Compensation - Summary of Restricted Stock Unit Activity (Detail) - 'Restricted Stock Units (RSUs) [Member]	12 Months Ended
	Dec. 31, 2022 $ / shares shares
Units
Unvested at December 31, 2021 \| shares	33,980
Granted \| shares	556,179
Vested \| shares	(35,149)
Forfeitures \| shares	(42,453)
Outstanding at December 31, 2022 \| shares	512,557
Unvested as of December 31, 2022 \| shares	512,557
Weighted-Average Grant Date Fair Value
Unvested at December 31, 2021 \| $ / shares	$ 41.29
Granted \| $ / shares	8.93
Vested \| $ / shares	35.45
Forfeitures \| $ / shares	19.45
Outstanding at December 31, 2022 \| $ / shares	8.39
Unvested as of December 31, 2022 \| $ / shares	$ 8.39

Equity-Based Compensation - Schedule of Equity-based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 7,537	$ 13,373	$ 11,629
Research and Development Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	2,756	6,289	5,822
General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 4,781	$ 7,084	4,956
Restructuring Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense			$ 851

Leases - Additional Information (Detail) $ in Thousands	1 Months Ended		12 Months Ended
Leases - Additional Information (Detail) $ in Thousands	Jun. 30, 2021 USD ($) ft²	Jan. 31, 2019	Dec. 31, 2022 USD ($) ft²	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Commitment And Contingencies [Line Items]
Future minimum rent commitment			$ 42,700
Future minimum lease commitment			2,570
Written off amount of the remaining lease liability			26,176
Written off amount of the right-of-use asset			28,949	$ 1,142
Proceeds from financing liabilities			2,143
Rent expense			$ 3,881	2,568	$ 2,562
Office Space [Member] \| Cambridge, Massachusetts [Member]
Commitment And Contingencies [Line Items]
Area of lease agreement \| ft²			5,000
Lease expiration period		2025-10
Written off amount of the right-of-use asset				1,233
Office Space [Member] \| MOROCCO
Commitment And Contingencies [Line Items]
Written off amount of the remaining lease liability				$ 1,314
Office laboratory [Member] \| Hood Park LLC [Member]
Commitment And Contingencies [Line Items]
Area of lease agreement \| ft²	49,869
Lease term	10 years
Lease renewal term	5 years
Lease description			The Company relocated its corporate headquarters to the Premises in June 2022. The initial term of the lease commenced in June 2022 when the construction of the lessor assets was substantially completed and continues for a ten-year period, unless earlier terminated
Operating lease, monthly payments	$ 305
Operating lease payments annual escalation percentage	3.00%
Construction allowance	$ 10,223
Letter of credit amount			$ 1,833

Leases - Future Minimum Payments for Operating and Finance Leases (Detail) $ in Thousands	Dec. 31, 2022 USD ($)
Finance Leases
2023	$ 1,109
2024	810
2025	651
Total future minimum lease payments	2,570
Less: Imputed Interest	199
Total Lease Liabilities	2,371
Operating Leases
2023	4,574
2024	4,195
2025	4,092
2026	4,118
Thereafter	25,721
Total future minimum lease payments	42,700
Less: Imputed Interest	16,524
Lease liability	$ 26,176

Leases - Supplemental Disclosure of Cash Flow Information Related to Leases (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Other information
Cash paid for amounts included in the measurement of lease liabilities	$ 2,840	$ 2,408	$ 2,408
Operating lease liabilities arising from obtaining right-of-use-assets	$ 29,126	$ 310	$ 1,629
Weighted-average remaining lease term (in years)
Operating lease	9 years 3 months 18 days	1 year	2 years 9 months 18 days
Finance lease	2 years 6 months	2 years 3 months 18 days	2 years 3 months 18 days
Weighted-average discount rate
Operating lease	10.60%	11.90%	12.60%
Finance lease	21.30%	10.70%	10.70%

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Office and Laboratory Lease [Member]
Commitment And Contingencies [Line Items]
Letter of credit outstanding amount	$ 1,833	$ 2,070

License Agreements - Additional Information (Detail) - USD ($)	1 Months Ended			12 Months Ended
	Feb. 28, 2022	Feb. 28, 2021	Oct. 31, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2016	Dec. 31, 2015
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense				$ 78,420,000	$ 58,739,000	$ 64,881,000
License agreement termination expiration term for licensed product						10 years
License agreement termination expiration term						5 years
University of Washington [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum milestone payment to be made								$ 1,000,000
Milestone payment upon achievement of certain milestones			$ 3,400,000
Amount payable in connection with execution of collaboration agreement			375,000
Research and development expense				96,000	60,000	$ 446,000
University of Missouri [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum milestone payment to be made								$ 1,000,000
Milestone payment upon achievement of certain milestones			$ 1,900,000
Research and development expense				133,000	195,000	2,111,000
Milestone payment	$ 1,300,000	$ 750,000
University of Missouri [Member] \| Ultragenyx [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount payable in connection with execution of collaboration agreement				1,300,000	750,000
University of Michigan [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum milestone payment to be made							$ 1,000,000
Research and development expense				$ 0	$ 37,000	35,000
University of Florida License Agreements [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum milestone payment to be made						2,900,000
License agreements termination description				Each of the agreements terminates on a licensed product-by-licensed product basis on the later of: (i) expiration of the patent rights covering such licensed product or (ii) ten (10) years from the first commercial sale of such licensed product.
University of Florida License Agreements [Member] \| AavantiBio, Inc [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment						$ 50,000

Net Loss per Share - Schedule of Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Earnings Per Share Basic [Line Items]
Net loss	$ (85,981)	$ (72,188)	$ (88,290)
Weighted average common stock outstanding basic	8,512,089	7,118,024	3,462,475
Weighted average common stock outstanding, diluted	8,512,089	7,118,024	3,462,475
Net loss per share, basic	$ (10.10)	$ (10.14)	$ (25.50)
Earnings Per Share, Diluted	$ (10.10)	$ (10.14)	$ (25.50)
Common Stock [Member]
Earnings Per Share Basic [Line Items]
Weighted average common stock outstanding basic	8,512,089	6,974,136	3,311,706
Weighted average common stock outstanding, diluted	8,512,089	6,974,136	3,311,706
Pre-Funded Warrants [Member]
Earnings Per Share Basic [Line Items]
Weighted average common stock outstanding basic		143,888	150,769
Weighted average common stock outstanding, diluted		143,888	150,769

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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-Paragraph 2
-Subparagraph (SX 210.5-03(25))
-URI https://asc.fasb.org/extlink&oid=126953954&loc=SL114868664-224227

+ Details

- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

+ References

+ Details

Net Loss per Share - Schedule of Antidilutive Securities Excluded from Calculation of Diluted Net Loss per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from calculation of diluted net loss per share	1,946,525	434,821	273,747
Options to Purchase Shares of Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from calculation of diluted net loss per share	1,433,968	400,842	207,851
Unvested Restricted Stock Units [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from calculation of diluted net loss per share	512,557	33,979	61,226
Unvested Shares of Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from calculation of diluted net loss per share			4,670

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Taxes [Line Items]
Income tax expense (benefit)	$ 0	$ 0
Uncertain tax position	0
Unrecognized tax benefits	0	0
Tax interest and penalties	0	$ 0
Domestic Tax Authority [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	259,924,000
Tax credits carryforwards	$ 43,404,000
Tax credit carryforwards, expiration period	2033
Percentage of annual deduction equal to annual taxable income	80.00%
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	$ 259,342,000
Operating loss carryforwards, expiration	$ 258,152,000
Operating loss carryforwards, expiration period	2038
Unlimited carryforward amount	$ 1,190,000
Tax credits carryforwards	$ 4,280,000
Tax credit carryforwards, expiration period	2033

Income Taxes - Schedule of Reconciliation of Income Taxes Computed by U.S. Federal Statutory Rate (Detail)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income tax computed at federal statutory tax rate	21.00%	21.00%
State taxes, net of federal benefit	7.40%	6.40%
Permanent differences	(1.40%)	0.50%
Bargain purchase gain	4.50%
Tax credits	11.50%	12.10%
Change in deferred tax rate	0.10%	0.30%
Stock compensation cancelations	(1.90%)	(1.90%)
Other	(0.60%)	0.10%
Valuation allowance	(40.60%)	(38.50%)
Total	0.00%	0.00%

Income Taxes - Schedule of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Tax loss carryforwards	$ 70,965	$ 60,405
Tax credit carryforwards	46,786	36,905
Deferred expenses	7,174	420
Accrued expenses	1,901	815
Stock compensation	7,839	7,821
Intangible assets	36,553	19,919
Depreciation	116	224
Other	166	2,373
Total deferred tax assets	171,500	128,882
Valuation allowance	(163,566)	(128,570)	$ (100,740)
Deferred tax liabilities:
Right-of-use asset	(7,934)	(312)
Total deferred tax liabilities	$ (7,934)	(312)
Net deferred taxes		$ 0

Income Taxes - Schedule of Deferred Income Tax Asset Valuation Allowance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Valuation allowance at beginning of year	$ 128,570	$ 100,740
Increases recorded to income tax provision	34,996	27,830
Valuation allowance at end of year	$ 163,566	$ 128,570

Defined Contribution Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Retirement Benefits [Abstract]
Company's contribution to the plan	$ 527,000	$ 241,000	$ 0

Restructuring- Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended	12 Months Ended
	Nov. 30, 2022	Apr. 30, 2022	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2020	Mar. 31, 2024
January 2020 Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges were paid					$ 1,882
Number of headcount reduced, percentage					30.00%
Restructuring charges related to severance payment and other employee-related costs					$ 1,944
April 2022 Plan [Member]
Restructuring Cost and Reserve [Line Items]
Number of headcount reduced, percentage		35.00%
Restructuring charges related to severance payment and other employee-related costs				$ 1,520
November 2022 Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges were paid				$ 1,737
Number of headcount reduced, percentage	18.00%
Restructuring charges related to severance payment and other employee-related costs			$ 5,658
November 2022 Plan [Member] \| Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges expected to be paid						$ 3,921

Restructuring - Schedule of Total Amount Incurred and Liability Related to Associated Restructuring Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Restructuring Cost and Reserve [Line Items]
Restructuring charges incurred during the period	$ 7,178		$ 1,944
January 2020 Restructuring Plan [Member] \| One-Time Employee Termination Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Accrued restructuring costs, Beginning balance		$ 62
Amounts paid during the period		$ (62)
Accrued restructuring costs, Ending balance			$ 62
April 2022 Corporate Strategy Change [Member] \| One-Time Employee Termination Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges incurred during the period	1,520
Amounts paid during the period	(1,520)
Accrued restructuring costs, Ending balance	0
November 2022 Workforce Reduction Plan [Member] \| One-Time Employee Termination Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges incurred during the period	5,658
Amounts paid during the period	(1,737)
Accrued restructuring costs, Ending balance	$ 3,921