Solid Biosciences (SLDB) 10-Q 16 Aug 21 2021 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2021	Aug. 10, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Trading Symbol	SLDB
Entity Registrant Name	Solid Biosciences Inc.
Entity Current Reporting Status	Yes
Entity Central Index Key	0001707502
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		110,296,992
Entity File Number	001-38360
Entity Tax Identification Number	90-0943402
Entity Address, Address Line One	141 Portland Street, Fifth Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
City Area Code	617
Local Phone Number	337-4680
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock $0.001 par value per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 200,609	$ 154,744
Available-for-sale securities	48,350
Prepaid expenses and other current assets	5,743	4,157
Restricted cash, current	90	0
Accounts receivable - related party	286
Total current assets	255,078	158,901
Property and equipment, net	7,128	8,153
Operating lease, right-of-use assets	1,581	3,579
Other non-current assets		209
Restricted cash, excluding current portion	2,070	327
Total assets	265,857	171,169
Current liabilities:
Accounts payable	3,003	3,274
Accrued expenses	7,714	8,640
Operating lease liabilities	1,499	1,999
Finance lease liabilities	220	208
Other current liabilities	61
Deferred revenue - related party	10,048	10,359
Total current liabilities	22,545	24,480
Operating lease liabilities, excluding current portion	656	2,419
Finance lease liabilities, excluding current portion	412	525
Deferred revenue - related party, excluding current portion	4,306	10,359
Other non-current liabilities		1,300
Total liabilities	27,919	39,083
Commitments and contingencies
Preferred stock, $0.001 par value; 10,000,000 shares authorized at June 30, 2021 and December 31, 2020; no shares issued and outstanding at June 30, 2021 and December 31, 2020
Common stock, $0.001 par value; 300,000,000 shares authorized at June 30, 2021 and December 31, 2020; 110,295,992 shares issued and outstanding at June 30, 2021 and 84,893,994 shares issued and outstanding at December 31, 2020; 2,158,329 pre-funded warrants outstanding at June 30, 2021 and December 31, 2020	112	87
Additional paid-in capital	678,001	536,568
Accumulated other comprehensive loss	(11)
Accumulated deficit	(440,164)	(404,569)
Total stockholders’ equity	237,938	132,086
Total liabilities and stockholders’ equity	$ 265,857	$ 171,169

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2021	Dec. 31, 2020
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	300,000,000	300,000,000
Common stock, shares issued	110,295,992	84,893,994
Common stock, shares outstanding	110,295,992	84,893,994
Pre-funded warrants outstanding	2,158,329	2,158,329

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Collaboration revenue - related party	$ 3,594		$ 6,929
Operating expenses:
Research and development	15,513	$ 13,448	29,719	$ 33,113
General and administrative	6,766	5,526	12,781	10,776
Restructuring charges				1,944
Total operating expenses	22,279	18,974	42,500	45,833
Loss from operations	(18,685)	(18,974)	(35,571)	(45,833)
Other income (expense):
Interest (expense) income	(13)	(13)	(27)	151
Other income	3		3	1
Total other income (expense), net	(10)	(13)	(24)	152
Net loss	$ (18,695)	$ (18,987)	$ (35,595)	$ (45,681)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.17)	$ (0.39)	$ (0.35)	$ (0.95)
Weighted average shares of common stock outstanding, basic and diluted	112,298,982	48,163,094	100,850,878	48,111,186

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (18,695)	$ (18,987)	$ (35,595)	$ (45,681)
Other comprehensive loss:
Unrealized (loss) gain on available-for-sale securities	(11)	1	(11)	(1)
Comprehensive loss	$ (18,706)	$ (18,986)	$ (35,606)	$ (45,682)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Changes in 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	$ 48	$ 396,278	$ 1	$ (316,279)
Beginning balance, units at Dec. 31, 2019		48,283,270
Equity-based compensation	6,347		6,347
Net loss	(45,681)				(45,681)
Vesting of restricted stock, units		121,975
Forfeiture of restricted stock awards units		(41,153)
Unrealized gain (loss) on available for sale securities	(1)			(1)
Ending balance at Jun. 30, 2020	40,713	$ 48	402,625		(361,960)
Ending balance, units at Jun. 30, 2020		48,364,092
Beginning balance at Mar. 31, 2020	56,456	$ 48	399,382	(1)	(342,973)
Beginning balance, units at Mar. 31, 2020		48,366,423
Equity-based compensation	3,243		3,243
Net loss	(18,987)				(18,987)
Forfeiture of restricted stock awards units		(2,331)
Unrealized gain (loss) on available for sale securities	1			1
Ending balance at Jun. 30, 2020	40,713	$ 48	402,625		(361,960)
Ending balance, units at Jun. 30, 2020		48,364,092
Beginning balance at Dec. 31, 2020	132,086	$ 87	536,568		(404,569)
Beginning balance, units at Dec. 31, 2020		87,052,323
Equity-based compensation	6,542		6,542
Sale of common stock, net of issuance costs	134,878	$ 25	134,853
Sale of common stock, net of issuance costs, shares		25,000,000
Exercise of stock options	38		38
Exercise of stock options, shares		10,625
Net loss	(35,595)				(35,595)
Vesting of restricted stock, units		419,193
Forfeiture of restricted stock awards units		(27,820)
Unrealized gain (loss) on available for sale securities	(11)			(11)
Ending balance at Jun. 30, 2021	237,938	$ 112	678,001	(11)	(440,164)
Ending balance, units at Jun. 30, 2021		112,454,321
Beginning balance at Mar. 31, 2021	253,000	$ 112	674,357		(421,469)
Beginning balance, units at Mar. 31, 2021		112,446,896
Equity-based compensation	3,635		3,635
Exercise of stock options	9		9
Exercise of stock options, shares		2,475
Net loss	(18,695)				(18,695)
Vesting of restricted stock, units		6,262
Forfeiture of restricted stock awards units		(1,312)
Unrealized gain (loss) on available for sale securities	(11)			(11)
Ending balance at Jun. 30, 2021	$ 237,938	$ 112	$ 678,001	$ (11)	$ (440,164)
Ending balance, units at Jun. 30, 2021		112,454,321

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) $ in Thousands	6 Months Ended
	Jun. 30, 2021USD ($)
Statement Of Stockholders Equity [Abstract]
Issuance costs	$ 8,872

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities:
Net loss	$ (35,595)	$ (45,681)
Adjustments to reconcile net loss to net cash used in operating activities:
Amortization of (discount)/premium on available-for-sale securities	7	(20)
Equity-based compensation expense	6,542	6,347
Depreciation expense	1,453	2,360
Gain on disposal of property and equipment	3
Changes in operating assets and liabilities:
Prepaid expenses and other current and non-current assets	621	362
Accounts receivable - related party	(286)
Accounts payable	(318)	(3,892)
Accrued expenses and other current and non-current liabilities	(4,529)	(1,818)
Deferred revenue- related party, current and non-current	(6,364)
Net cash used in operating activities	(38,466)	(42,342)
Cash flows from investing activities:
Purchases of property and equipment	(384)	(759)
Proceeds from sale and maturities of available-for-sale securities		7,900
Purchases of available-for-sale securities	(48,368)	(401)
Net cash (used in) provided by investing activities	(48,752)	6,740
Cash flows from financing activities:
Proceeds from issuance of common stock	134,878
Proceeds from exercise of stock options	38
Net cash provided by financing activities	134,916
Net increase/(decrease) in cash, cash equivalents and restricted cash	47,698	(35,602)
Cash, cash equivalents, and restricted cash at beginning of period	155,071	76,370
Cash, cash equivalents, and restricted cash at end of period	202,769	40,768
Supplemental disclosure of non-cash investing and financing activities:
Change in unrealized loss	(11)
Decrease in right of use asset due to lease termination	(1,233)
Property and equipment included in accounts payable and accruals	$ 47	$ 27

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	6 Months Ended
	Jun. 30, 2021
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. In October 2013, the company changed its name to Solid Ventures, LLC and in June 2015, the company changed its name to Solid Biosciences, LLC. The company operated as a Delaware limited liability company under the name Solid Biosciences, LLC 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”). In addition, entities formed solely for the purpose of holding membership interests in the Company’s limited liability company were merged with and into the Company. As a result of the Corporate Conversion, all of the Series 1 and 2 Senior Preferred, Junior Preferred Units, Series A, B, C and D Common Units of Solid Biosciences, LLC converted into shares of common stock of Solid Biosciences Inc. on a one for 0.8485 basis and all of the unit holders of Solid Biosciences, LLC became holders of common stock of Solid Biosciences Inc. The Company’s mission is to cure Duchenne muscular dystrophy (“Duchenne”), a genetic muscle-wasting disease predominantly affecting boys. It is caused by mutations in the dystrophin gene, which result in the absence or near-absence of dystrophin protein. Dystrophin protein works to strengthen muscle fibers and protect them from daily wear and tear. Without functioning dystrophin and certain associated proteins, muscles suffer excessive damage from normal daily activities and are unable to regenerate, leading to the build-up of fibrotic, or scar, and fat tissue. The Company’s lead product candidate, SGT-001, is a gene transfer candidate under investigation for its ability to drive functional dystrophin protein expression in patients’ muscles and improve the course of the disease. SGT-001 has been granted Rare Pediatric Disease Designation and Fast Track Designation in the United States and Orphan Drug Designations in both the United States and European Union. The Company filed an Investigational New Drug application (“IND”) in September 2017 and initiated a Phase I/II clinical trial for SGT-001 in the United States during the fourth quarter of 2017 , which is called IGNITE DMD. In November 2019, IGNITE DMD was placed on clinical hold by the U.S. Food and Drug Administration (“FDA”). In April 2020, the Company submitted a response to the FDA that included changes to the clinical protocol designed to enhance patient safety, as well as information related to improvements to its manufacturing process. The FDA responded by maintaining the clinical hold and requesting further data and analyses relating to this manufacturing process. In June 2020, the Company submitted a response to the FDA that provided data related to manufacturing process improvements. In July 2020, the Company announced that the FDA responded by maintaining the clinical hold and requesting further manufacturing information and updated safety and efficacy data for all patients dosed in the trial, as well as providing direction on the total viral load to be administered per patient. In October 2020, the Company announced that the FDA lifted the clinical hold placed on the Company’s IGNITE DMD Phase I/II clinical trial. In February 2021, the Company resumed treatment of patients in the IGNITE DMD clinical trial. 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 product 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. Liquidity The accompanying condensed 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 June 30, 2021, the Company has funded its operations primarily with the proceeds from the sale of redeemable preferred units and member units, 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 sales under its at-the-market sales agreement. 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 June 30, 2021, the Company had an accumulated deficit of $440,164. During the three and six months ended June 30, 2021, the Company incurred a net loss of $18,695 and $35,595, respectively, 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 condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed consolidated financial statements include the accounts of Solid Biosciences Inc. and its wholly owned or controlled subsidiaries. All intercompany accounts and transactions have been eliminated. In the opinion of management, the Company’s accompanying unaudited condensed consolidated financial statements include all adjustments, consisting of normal recurring accruals, necessary for a fair statement of the Company’s financial statements for interim periods in accordance with GAAP. The information included in this quarterly report on Form 10-Q should be read in conjunction with the Company’s consolidated financial statements and the accompanying notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020. The year-end condensed consolidated balance sheet data presented for comparative purposes was derived from the Company’s audited financial statements but does not include all disclosures required by GAAP.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies The Company’s accounting policies are described in the “Notes to Consolidated Financial Statements” in its Annual Report on Form 10-K for the year ended December 31, 2020 and updated, as necessary, in this report. Use of Estimates The preparation of the Company’s condensed 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 condensed consolidated financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these condensed 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 $2,160 and $327 in separate restricted bank accounts as security deposits for leases of the Company’s facilities as of June 30, 2021 and December 31, 2020, respectively. As of June 30, 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: June 30, 2021 December 31, 2020 Cash and cash equivalents as presented on balance sheet $ 200,609 $ 154,744 Restricted cash, current, as presented on balance sheet 90 — Restricted cash, non-current, as presented on balance sheet 2,070 327 Cash and cash equivalents and restricted cash as presented on cash flow statement $ 202,769 $ 155,071 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. 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. In June 2021, the Company entered into a lease with Hood Park LLC (“Landlord”), pursuant to which the Company will lease approximately 49,869 square feet of office, laboratory, research and development and manufacturing space located in Charlestown, Massachusetts (“Premises”). The Company intends to relocate its corporate headquarters to the Premises in early 2022. The term of the lease commences on the later of (i) the date the Landlord delivers the Premises to the Company or (ii) the earlier of (a) the date the Company’s work on the Premises is substantially completed, (b) the date the Company commences business operations in the Premises, or (c) the one hundred twentieth (120th) day following the Landlord’s satisfaction of item (i) above. The lease commencement date is anticipated to be in the first quarter of 2022. The date on which the Company will become responsible for paying rent under the lease will be 61 days following the lease commencement date. The initial term of the lease will be for a ten-year five-year As of June 30, 2021, the lease had not commenced. For the three and six months ended June 30, 2021, the Company incurred approximately $348 of tenant improvement allowance receivable. 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. Segment Data The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on developing treatments through gene therapy and other means for patients with Duchenne. All of the Company’s tangible assets are held in the United States. Related Parties 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 7,825,797 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, or Danforth, an affiliate of Stephen DiPalma, the Company’s interim chief financial officer. Pursuant to the consulting agreement, Danforth provides 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 $313 to date. In accordance with the consulting agreement, in November 2020, the Company issued to Danforth a warrant to purchase 30,000 shares of the Company’s common stock at an exercise price per share of $3.29. The consulting agreement may be terminated by either party without cause upon 60 days’ prior written notice to the other party and with cause upon 30 days’ prior written notice to the other party. Recently Adopted Accounting Pronouncements In August 2018 the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2018-13 , Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which was subsequently modified by several ASU’s issued in 2018 and 2019

Collaborations

Collaborations	6 Months Ended
	Jun. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaborations	3. Collaborations Ultragenyx Collaboration Agreement Collaboration Agreement On October 22, 2020 (the “Effective Date”), the Company entered into a collaboration and license agreement with Ultragenyx Pharmaceutical Inc. to focus on the development and commercialization of new gene therapies for Duchenne Muscular Dystrophy. 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 Muscular Dystrophy 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 existing SGT-001 program. The Company will conduct certain research and development activities with respect to the development of the Licensed Products. Ultragenyx will reimburse the Company for personnel and out-of-pocket costs that the Company incurs in conducting such development 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 archives 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 October 22, 2020 (the “Closing Date”), pursuant to which the Company issued and sold 7,825,797 shares of its common stock (the “Shares”) to Ultragenyx at a price of $5.1113 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 June 30, 2021 % 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 the Shares will be subject to a lock-up restriction, such that Ultragenyx will not, and will also cause its affiliates not to, without the prior approval of the Company and with certain exceptions, sell, transfer or otherwise dispose of the Shares until the earliest to occur of (i) 18 months after the Effective Date, (ii) the termination of the Collaboration Agreement or (iii) other specified events. 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 (iii) 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. During the three and six months ended June 30, 2021, the Company recognized $3,594 and $6,929, respectively, of related party collaboration revenue, associated with its collaboration with Ultragenyx related to research and development services performed during the period and the corresponding cost reimbursement receivable. The following table presents changes in the balances of the Company’s related party collaboration receivables and contract liabilities during the three and six months ended June 30, 2021: Balance as of March 31, 2021 Additions Deductions Balance as of June 30, 2021 Related party collaboration receivable $ 280 $ 286 $ (280 ) $ 286 Contract liabilities: Deferred revenue 17,663 — (3,309 ) 14,354 Balance as of December 31, 2020 Additions Deductions Balance as of June 30, 2021 Related party collaboration receivable $ — $ 566 $ (280 ) $ 286 Contract liabilities: Deferred revenue 20,718 — (6,364 ) 14,354 The change in receivables balance for the three and six months ended June 30, 2021 is driven by amounts owed to the Company for research and development services provided, partially offset by $280 in collections received As of June 30, 2021, there was $14,354 of deferred revenue related to the Ultragenyx Collaboration Agreement, which is classified as either current or non-current in the accompanying condensed consolidated balance sheet based on the period the services are expected to be delivered. Additionally, as of June 30, 2021, there was $286 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 Ultragenyx Collaboration Programs 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 condensed consolidated statement of operations during the three and six months ended June 30, 2021.

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	6 Months Ended
	Jun. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities	4. 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 June 30, 2021 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ — $ 155,757 $ — $ 155,757 Available-for-sale securities $ — $ 48,350 $ — $ 48,350 $ — $ 204,107 $ — $ 204,107 Fair Value Measurements as of December 31, 2020 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ — $ 84,462 $ — $ 84,462 $ — $ 84,462 $ — $ 84,462 As of The fair value of the Company’s cash, restricted cash, accounts payable, and accrued expenses and other current liabilities approximate their carrying value due to their short-term maturities.

Available-for-Sale Securities

Available-for-Sale Securities	6 Months Ended
	Jun. 30, 2021
Investments Debt And Equity Securities [Abstract]
Available-for-Sale Securities	5. Available-for-Sale Securities As of June 30, 2021, the fair value of available-for-sale securities by type of security was as follows: June 30, 2021 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Corporate bond securities $ 38,366 $ — $ (11 ) $ 38,355 Commercial paper $ 9,995 $ — $ — $ 9,995 $ 48,361 $ — $ (11 ) $ 48,350 As of December 31, 2020, there were no available-for-sale securities. The estimated fair value and amortized cost of the Company’s available-for-sale securities by contractual maturity are summarized as follows: June 30, 2021 Amortized Cost Fair Value Due in one year or less $ 48,361 $ 48,350 Total available-for-sale securities $ 48,361 $ 48,350 The weighted average maturity of the Company’s available-for-sale securities as of June 30, 2021 was approximately 0.5 years. As of December 31, 2020, there were no available-for-sale securities

Property and Equipment

Property and Equipment	6 Months Ended
	Jun. 30, 2021
Property Plant And Equipment [Abstract]
Property and Equipment	6. Property and Equipment Property and equipment consists of the following: June 30, 2021 December 31, 2020 Furniture and fixtures $ 213 $ 203 Laboratory equipment 9,849 9,631 Leasehold improvements 4,713 4,713 Computer equipment 436 436 Computer software 553 553 Construction in process 1,520 1,330 17,284 16,866 Less accumulated depreciation 10,156 8,713 $ 7,128 $ 8,153 Depreciation expense was $718 and $1,453 for the three and six months ended June 30, 2021.

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	6 Months Ended
	Jun. 30, 2021
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: June 30, 2021 December 31, 2020 Prepaid research and development expenses $ 1,953 $ 2,674 Tenant improvement allowance receivable 348 - Prepaid expenses and other assets 3,442 1,483 $ 5,743 $ 4,157

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	6 Months Ended
	Jun. 30, 2021
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	8. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consist of the following: June 30, 2021 December 31, 2020 Accrued research and development $ 2,389 $ 2,091 Accrued compensation 1,810 3,834 Accrued other 3,515 2,715 $ 7,714 $ 8,640

Stockholders' Equity

Stockholders' Equity	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Stockholders' Equity	9. Stockholders’ Equity In July 2019, the Company issued and sold in a private placement (i) 10,607,525 shares of its common stock at a price per share of $4.65 and (ii) 2,295,699 pre-funded warrants to purchase shares of its common stock at a price per warrant of $4.64. Each pre-funded warrant is exercisable for one share of common stock at an exercise price of $0.01 and the pre-funded warrants have no expiration date. The Company received gross proceeds from the private placement of $59,977, before deducting offering costs of $2,102. In October 2020, 137,460 of these pre-funded warrants were exercised. No warrants were exercised during the three and six months ended June 30, 2021 and 2020. In October 2020, in connection with the execution of the Collaboration Agreement, Ultragenyx and the Company also entered into the Stock Purchase Agreement, pursuant to which the Company issued and sold 7,825,797 shares of its common stock to Ultragenyx at a price of $5.1113 per share for an aggregate purchase price of approximately $40,000. In October 2020, the Company sold 6,309,632 shares of common stock pursuant to a sales agreement (the “ATM Sales Agreement”), by and between the Company and Jefferies LLC (“Jefferies”), In December 2020, the Company issued and sold in a private placement 24,324,320 shares of its common stock at a price per share of $3.70. The Company received net proceeds from the private placement of $86,210 after deducting placement agent fees and offering expenses of $3,790. In March 2021, the Company issued and sold in a public offering 25,000,000 shares of its common stock at a price to the public of $5.575 per share. The Company received net proceeds of $134,878 after deducting underwriting discounts and commissions and offering expenses.

Equity-Based Compensation

Equity-Based Compensation	6 Months Ended
	Jun. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity-Based Compensation	10. Equity-Based Compensation In connection with the closing of the Company’s initial public offering, the board of directors and stockholders approved the 2018 Omnibus Incentive Plan, which provides for the reservation of 5,001,000 shares of common stock for equity awards. On June 16, 2020, the Company’s stockholders approved the 2020 Equity Incentive Plan (“2020 Plan”) which consists of (i) 3,000,000 shares of common stock and (ii) additional shares of common stock (up to 4,879,025) as is equal to (i) the number of shares reserved under the Company’s 2018 Omnibus Incentive Plan (“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. In June 2021, the Company’s stockholders approved an amendment to the 2020 Plan to reserve an additional 7,000,000 shares of common stock for issuance under the plan. In June 2021, the Company’s stockholders also approved the 2021 Employee Stock Purchase Plan (“ESPP”), which provides for 1,102,885 shares to be available for purchase by eligible employees according to its terms. During the three and six months ended June 30, 2021, the Company granted options for the purchase of 604,400 and 3,001,895, respectively, shares of common stock. During the three and six months ended June 30, 2021, the Company granted no restricted stock units. 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 condensed consolidated statements of operations: Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Research and development $ 1,992 $ 1,616 $ 3,482 $ 2,855 General and administrative 1,643 1,627 3,060 2,641 Restructuring — — — 851 Total $ 3,635 $ 3,243 $ 6,542 $ 6,347

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes During the three and six months ended June 30, 2021 and 2020, the Company recorded no income tax benefits for the net operating losses incurred or for the research and development tax credits and orphan drug credits generated in each year due to its uncertainty of realizing a benefit from those items. The Company has provided a valuation allowance for the full amount of its net deferred tax assets because, at June 30, 2021 and December 31, 2020, it was more likely than not that any future benefit from deductible temporary differences and net operating loss and tax credit carryforwards would not be realized. As of June 30, 2021 and December 31, 2020, the Company had not recorded any amounts for unrecognized tax benefits. The Company files income 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, 2018 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.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	12. Commitments and Contingencies 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 June 30, 2021.

Net Loss per Share

Net Loss per Share	6 Months Ended
	Jun. 30, 2021
Earnings Per Share [Abstract]
Net Loss per Share	13. Net Loss per Share Basic and diluted net loss per share attributable to common stockholders were calculated as follows: The numerator for basic and diluted net loss per share attributable to common stockholders is as follows: Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Net loss attributable to common stockholders $ (18,695 ) $ (18,987 ) $ (35,595 ) $ (45,681 ) The denominator is as follows: Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Weighted average shares of common stock outstanding, basic and diluted 110,140,653 48,163,094 98,692,549 48,111,186 Weighted average shares of pre-funded warrants to purchase common stock 2,158,329 — 2,158,329 — Total 112,298,982 48,163,094 100,850,878 48,111,186 Net loss per share attributable to common stockholders, basic and diluted is as follows: Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Net loss per share attributable to common stockholders $ (0.17 ) $ (0.39 ) $ (0.35 ) $ (0.95 ) 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 attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect for the six months ended June 30: 2021 2020 Options to purchase shares of common stock 5,602,998 3,607,953 Unvested shares of common stock 13,008 184,171 Unvested restricted stock units 312,264 1,421,095 5,928,270 5,213,219

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of the Company’s condensed 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 condensed consolidated financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these condensed 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	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	Restricted Cash The Company held restricted cash of $2,160 and $327 in separate restricted bank accounts as security deposits for leases of the Company’s facilities as of June 30, 2021 and December 31, 2020, respectively. As of June 30, 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: June 30, 2021 December 31, 2020 Cash and cash equivalents as presented on balance sheet $ 200,609 $ 154,744 Restricted cash, current, as presented on balance sheet 90 — Restricted cash, non-current, as presented on balance sheet 2,070 327 Cash and cash equivalents and restricted cash as presented on cash flow statement $ 202,769 $ 155,071
Leases	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. 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. In June 2021, the Company entered into a lease with Hood Park LLC (“Landlord”), pursuant to which the Company will lease approximately 49,869 square feet of office, laboratory, research and development and manufacturing space located in Charlestown, Massachusetts (“Premises”). The Company intends to relocate its corporate headquarters to the Premises in early 2022. The term of the lease commences on the later of (i) the date the Landlord delivers the Premises to the Company or (ii) the earlier of (a) the date the Company’s work on the Premises is substantially completed, (b) the date the Company commences business operations in the Premises, or (c) the one hundred twentieth (120th) day following the Landlord’s satisfaction of item (i) above. The lease commencement date is anticipated to be in the first quarter of 2022. The date on which the Company will become responsible for paying rent under the lease will be 61 days following the lease commencement date. The initial term of the lease will be for a ten-year five-year As of June 30, 2021, the lease had not commenced. For the three and six months ended June 30, 2021, the Company incurred approximately $348 of tenant improvement allowance receivable. 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.
Segment Data	Segment Data The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on developing treatments through gene therapy and other means for patients with Duchenne. All of the Company’s tangible assets are held in the United States.
Related Parties	Related Parties 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 7,825,797 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, or Danforth, an affiliate of Stephen DiPalma, the Company’s interim chief financial officer. Pursuant to the consulting agreement, Danforth provides 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 $313 to date. In accordance with the consulting agreement, in November 2020, the Company issued to Danforth a warrant to purchase 30,000 shares of the Company’s common stock at an exercise price per share of $3.29. The consulting agreement may be terminated by either party without cause upon 60 days’ prior written notice to the other party and with cause upon 30 days’ prior written notice to the other party.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In August 2018 the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2018-13 , Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which was subsequently modified by several ASU’s issued in 2018 and 2019

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2021
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: June 30, 2021 December 31, 2020 Cash and cash equivalents as presented on balance sheet $ 200,609 $ 154,744 Restricted cash, current, as presented on balance sheet 90 — Restricted cash, non-current, as presented on balance sheet 2,070 327 Cash and cash equivalents and restricted cash as presented on cash flow statement $ 202,769 $ 155,071

Collaborations (Tables)

Collaborations (Tables)	6 Months Ended
	Jun. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Summary of Changes in Balances of Company's Related Party Collaboration Receivables and Contract Liabilities	The following table presents changes in the balances of the Company’s related party collaboration receivables and contract liabilities during the three and six months ended June 30, 2021: Balance as of March 31, 2021 Additions Deductions Balance as of June 30, 2021 Related party collaboration receivable $ 280 $ 286 $ (280 ) $ 286 Contract liabilities: Deferred revenue 17,663 — (3,309 ) 14,354 Balance as of December 31, 2020 Additions Deductions Balance as of June 30, 2021 Related party collaboration receivable $ — $ 566 $ (280 ) $ 286 Contract liabilities: Deferred revenue 20,718 — (6,364 ) 14,354

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	6 Months Ended
	Jun. 30, 2021
Fair Value Disclosures [Abstract]
Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis and Indicate Level of Fair Value Hierarchy Utilized	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 June 30, 2021 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ — $ 155,757 $ — $ 155,757 Available-for-sale securities $ — $ 48,350 $ — $ 48,350 $ — $ 204,107 $ — $ 204,107 Fair Value Measurements as of December 31, 2020 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ — $ 84,462 $ — $ 84,462 $ — $ 84,462 $ — $ 84,462

Available-for-Sale Securities (

Available-for-Sale Securities (Tables)	6 Months Ended
	Jun. 30, 2021
Investments Debt And Equity Securities [Abstract]
Schedule of Fair Value of Available-for-Sale Securities by Type of Security	As of June 30, 2021, the fair value of available-for-sale securities by type of security was as follows: June 30, 2021 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Corporate bond securities $ 38,366 $ — $ (11 ) $ 38,355 Commercial paper $ 9,995 $ — $ — $ 9,995 $ 48,361 $ — $ (11 ) $ 48,350
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: June 30, 2021 Amortized Cost Fair Value Due in one year or less $ 48,361 $ 48,350 Total available-for-sale securities $ 48,361 $ 48,350

Property and Equipment (Tables)

Property and Equipment (Tables)	6 Months Ended
	Jun. 30, 2021
Property Plant And Equipment [Abstract]
Summary of Property and Equipment	Property and equipment consists of the following: June 30, 2021 December 31, 2020 Furniture and fixtures $ 213 $ 203 Laboratory equipment 9,849 9,631 Leasehold improvements 4,713 4,713 Computer equipment 436 436 Computer software 553 553 Construction in process 1,520 1,330 17,284 16,866 Less accumulated depreciation 10,156 8,713 $ 7,128 $ 8,153

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	6 Months Ended
	Jun. 30, 2021
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: June 30, 2021 December 31, 2020 Prepaid research and development expenses $ 1,953 $ 2,674 Tenant improvement allowance receivable 348 - Prepaid expenses and other assets 3,442 1,483 $ 5,743 $ 4,157

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	6 Months Ended
	Jun. 30, 2021
Payables And Accruals [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following: June 30, 2021 December 31, 2020 Accrued research and development $ 2,389 $ 2,091 Accrued compensation 1,810 3,834 Accrued other 3,515 2,715 $ 7,714 $ 8,640

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Equity-based Compensation Expense	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 condensed consolidated statements of operations: Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Research and development $ 1,992 $ 1,616 $ 3,482 $ 2,855 General and administrative 1,643 1,627 3,060 2,641 Restructuring — — — 851 Total $ 3,635 $ 3,243 $ 6,542 $ 6,347

Net Loss per Share (Tables)

Net Loss per Share (Tables)	6 Months Ended
	Jun. 30, 2021
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Loss per Share Attributable to Common Stockholders	The numerator for basic and diluted net loss per share attributable to common stockholders is as follows: Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Net loss attributable to common stockholders $ (18,695 ) $ (18,987 ) $ (35,595 ) $ (45,681 ) The denominator is as follows: Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Weighted average shares of common stock outstanding, basic and diluted 110,140,653 48,163,094 98,692,549 48,111,186 Weighted average shares of pre-funded warrants to purchase common stock 2,158,329 — 2,158,329 — Total 112,298,982 48,163,094 100,850,878 48,111,186 Net loss per share attributable to common stockholders, basic and diluted is as follows: Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Net loss per share attributable to common stockholders $ (0.17 ) $ (0.39 ) $ (0.35 ) $ (0.95 )
Schedule of Antidilutive Securities Excluded from Calculation of Diluted Net Loss per Share Attributable to Common Stockholders	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 attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect for the six months ended June 30: 2021 2020 Options to purchase shares of common stock 5,602,998 3,607,953 Unvested shares of common stock 13,008 184,171 Unvested restricted stock units 312,264 1,421,095 5,928,270 5,213,219

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Jan. 25, 2018
Nature Of Business And Basis Of Presentation [Line Items]
Net loss	$ 18,695	$ 18,987	$ 35,595	$ 45,681
Accumulated deficit	440,164		440,164		$ 404,569
Net cash used in operating activities			38,466	$ 42,342
Cash, cash equivalents and available-for-sale securities	$ 248,959		$ 248,959
Corporate Conversion [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Common stock, conversion ratio						84.85%

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended
	Nov. 30, 2020USD ($)$ / sharesshares	Jun. 30, 2021USD ($)ft²shares	Jun. 30, 2021USD ($)ft²shares	Dec. 31, 2020USD ($)shares	Oct. 31, 2020shares
Significant Accounting Policies [Line Items]
Restricted cash deposit		$ 2,160	$ 2,160	$ 327
Restricted cash noncurrent		2,070	2,070	327
Restricted cash, current		90	90	0
Operating lease, right-of-use assets		$ 1,581	$ 1,581	$ 3,579
Common stock, shares issued | shares		110,295,992	110,295,992	84,893,994
Payment of exchange fees	$ 313
Common stock shares issued warrant to purchase | shares	30,000
Common stock warrants exercise price per share | $ / shares	$ 3.29
Agreement termination period	60 days
Agreement written notice period	30 days
ASU 2018-13 [Member]
Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adoption date		Jan. 1, 2020	Jan. 1, 2020
Change in accounting principle, accounting standards update, adopted		true	true
Change in accounting principle, accounting standards update, immaterial effect		true	true
ASU 2019-12 [Member]
Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adoption date		Jan. 1, 2021	Jan. 1, 2021
Change in accounting principle, accounting standards update, adopted		true	true
Change in accounting principle, accounting standards update, immaterial effect		true	true
Ultragenyx [Member] | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement [Member]
Significant Accounting Policies [Line Items]
Common stock, shares issued | shares					7,825,797
Office laboratory [Member] | Hood Park LLC [Member]
Significant Accounting Policies [Line Items]
Area of lease agreement | ft²		49,869	49,869
Lease description			The Company intends to relocate its corporate headquarters to the Premises in early 2022. The term of the lease commences on the later of (i) the date the Landlord delivers the Premises to the Company or (ii) the earlier of (a) the date the Company’s work on the Premises is substantially completed, (b) the date the Company commences business operations in the Premises, or (c) the one hundred twentieth (120th) day following the Landlord’s satisfaction of item (i) above. The lease commencement date is anticipated to be in the first quarter of 2022. The date on which the Company will become responsible for paying rent under the lease will be 61 days following the lease commencement date.
Lease term		10 years	10 years
Lease renewal term		5 years	5 years
Letter of credit amount		$ 1,833	$ 1,833
Tenant improvement allowance receivable		348	348
Lease liability		1,314	1,314
Operating lease, right-of-use assets		$ 1,233	$ 1,233

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Reconciliation of Amounts From Cash Flow Statement to Balance Sheet (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Reconciliation Of Beginning And End Of Period Amounts From Cash Flow Statement To Balance Sheet [Abstract]
Cash and cash equivalents as presented on balance sheet	$ 200,609	$ 154,744
Restricted cash, current	90	0
Restricted cash, non-current, as presented on balance sheet	2,070	327
Cash and cash equivalents and restricted cash as presented on cash flow statement	$ 202,769	$ 155,071	$ 40,768	$ 76,370

Collaborations - Additional Inf

Collaborations - Additional Information (Detail) - USD ($)	Oct. 22, 2020	Jun. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from issuance of common stock			$ 134,878,000
Related party revenue recognized		$ 3,594,000	6,929,000
Related party collaboration receivables		286,000	286,000
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	7,825,797
Common stock issued price per share	$ 5.1113
Proceeds from issuance of common stock	$ 40,000,000
Percentage of outstanding common stock	14.45%
Proceeds from equity investment under stock purchase agreement			$ 22,513,000
Transaction price			0
Related party revenue recognized		3,594,000	6,929,000
Proceeds from collaborators		280,000	280,000
Deferred revenue - related party		14,354,000	14,354,000	$ 17,663,000	$ 20,718,000	$ 14,354,000
Related party collaboration receivables		$ 286,000	286,000	$ 280,000		$ 286,000
Maximum [Member] | Ultragenyx [Member] | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement [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
Percentage of outstanding common stock			10.00%
Minimum [Member] | Ultragenyx [Member] | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of outstanding common stock			10.00%

Collaborations - Summary of Cha

Collaborations - Summary of Changes in Balances of Company's Related Party Collaboration Receivables and Contract Liabilities (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2021
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Related party collaboration receivable, Ending balance	$ 286	$ 286
Ultragenyx [Member] | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Related party collaboration receivable, Beginning balance	280
Related party collaboration receivable, Additions	286	566
Related party collaboration receivable, Deductions	(280)	(280)
Related party collaboration receivable, Ending balance	286	286
Deferred revenue, Beginning balance	17,663	20,718
Deferred revenue, Deductions	(3,309)	(6,364)
Deferred revenue, Ending balance	$ 14,354	$ 14,354

Fair Value of Financial Asset_3

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 ($)	Jun. 30, 2021	Dec. 31, 2020
Assets:
Cash equivalents	$ 155,757,000	$ 84,462,000
Available-for-sale securities	48,350,000	0
Assets Fair Value Disclosure	204,107,000	84,462,000
Level 2 [Member]
Assets:
Cash equivalents	155,757,000	84,462,000
Available-for-sale securities	48,350,000
Assets Fair Value Disclosure	$ 204,107,000	$ 84,462,000

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair value, assets, level 1 to level 2 transfers, amount	$ 0	$ 0
Fair value, assets, level 2 to level 1 transfers, amount	0	0
Fair value, assets, transfers into level 3, amount	0	0
Fair value, assets, transfers out of level 3, amount	$ 0	$ 0

Available-for-Sale Securities -

Available-for-Sale Securities - Schedule of Fair Value of Available-for-Sale Securities by Type of Security (Detail) - USD ($)	Jun. 30, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 48,361,000
Gross Unrealized Loss	(11,000)
Fair Value	48,350,000	$ 0
Corporate Bond Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	38,366,000
Gross Unrealized Loss	(11,000)
Fair Value	38,355,000
Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	9,995,000
Fair Value	$ 9,995,000

Available-for-Sale Securities_2

Available-for-Sale Securities - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Available-for-sale securities	$ 48,350,000	$ 0
Available-for-sale securities average maturity period	6 months

Available-for-Sale Securities_3

Available-for-Sale Securities - Summary Estimated Fair Value and Amortized Cost of Available-for-Sale Securities by Contractual Maturity (Detail) - USD ($)	Jun. 30, 2021	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Due in one year or less, amortized cost	$ 48,361,000
Amortized Cost	48,361,000
Due in one year or less, fair value	48,350,000
Total available-for-sale securities, fair value	$ 48,350,000	$ 0

Property and Equipment - Summar

Property and Equipment - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 17,284	$ 16,866
Less accumulated depreciation	10,156	8,713
Property and equipment, net	7,128	8,153
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	213	203
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	9,849	9,631
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,713	4,713
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	436	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	$ 1,520	$ 1,330

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2021	Jun. 30, 2020
Property Plant And Equipment [Abstract]
Depreciation expense	$ 718	$ 1,453	$ 2,360

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid research and development expenses	$ 1,953	$ 2,674
Tenant improvement allowance receivable	348
Prepaid expenses and other assets	3,442	1,483
Prepaid expenses and other current assets	$ 5,743	$ 4,157

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	$ 7,714	$ 8,640
Accrued Research and Development [Member]
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	2,389	2,091
Accrued Compensation [Member]
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	1,810	3,834
Accrued Other [Member]
Accrued Expenses And Other Current Liabilities [Line Items]
Accrued expenses and other current liabilities	$ 3,515	$ 2,715

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Oct. 22, 2020	Mar. 31, 2021	Dec. 31, 2020	Oct. 31, 2020	Jul. 31, 2019	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Nov. 30, 2020
Class Of Stock [Line Items]
Common stock warrants exercise price per share										$ 3.29
Gross proceeds from private placement					$ 59,977
Proceeds from issuance of common stock								$ 134,878
Ultragenyx [Member] | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement [Member]
Class Of Stock [Line Items]
Common stock issued price per share	$ 5.1113
Issued and sold shares of common stock	7,825,797
Proceeds from issuance of common stock	$ 40,000
Private Placement [Member]
Class Of Stock [Line Items]
Offering costs			$ 3,790		$ 2,102
ATM Sales Agreement [Member]
Class Of Stock [Line Items]
Stock issued and sold				6,309,632
Proceeds from issuance of common stock				$ 23,209
Public Offering [Member]
Class Of Stock [Line Items]
Stock issued and sold		25,000,000
Common stock issued price per share		$ 5.575
Proceeds from issuance of common stock		$ 134,878
Common Stock [Member]
Class Of Stock [Line Items]
Stock issued and sold								25,000,000
Common Stock [Member] | Private Placement [Member]
Class Of Stock [Line Items]
Stock issued and sold			24,324,320		10,607,525
Common stock issued price per share			$ 3.70		$ 4.65
Net proceeds from private placement			$ 86,210
Pre-Funded Warrants [Member]
Class Of Stock [Line Items]
Warrants exercised				137,460		0	0	0	0
Pre-Funded Warrants [Member] | Private Placement [Member]
Class Of Stock [Line Items]
Warrants to purchase common stock					2,295,699
Warrants price per share					$ 4.64
Warrants exercisable for common stock					1
Common stock warrants exercise price per share					$ 0.01

Equity-Based Compensation - Add

Equity-Based Compensation - Additional Information (Detail) - shares	Jun. 16, 2020	Jun. 30, 2021	Jun. 30, 2021	Jun. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock purchased			604,400	3,001,895
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted			0	0
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		5,001,000	5,001,000	5,001,000
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	3,000,000
Number of additional shares authorized for common stock for equity awards		7,000,000
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	4,879,025
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		1,102,885	1,102,885	1,102,885

Equity-Based Compensation - Sch

Equity-Based Compensation - Schedule of Equity-based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 3,635	$ 3,243	$ 6,542	$ 6,347
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,992	1,616	3,482	2,855
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,643	$ 1,627	$ 3,060	2,641
Restructuring [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense				$ 851

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 0	$ 0	$ 0	$ 0
Unrecognized tax benefits	$ 0		$ 0		$ 0

Net Loss per Share - Schedule o

Net Loss per Share - Schedule of Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share Basic [Line Items]
Net loss attributable to common stockholders	$ (18,695)	$ (18,987)	$ (35,595)	$ (45,681)
Weighted average shares of common stock outstanding, basic and diluted	112,298,982	48,163,094	100,850,878	48,111,186
Net loss per share attributable to common stockholders	$ (0.17)	$ (0.39)	$ (0.35)	$ (0.95)
Common Stock [Member]
Earnings Per Share Basic [Line Items]
Weighted average shares of common stock outstanding, basic and diluted	110,140,653	48,163,094	98,692,549	48,111,186
Pre-Funded Warrants [Member]
Earnings Per Share Basic [Line Items]
Weighted average shares of common stock outstanding, basic and diluted	2,158,329		2,158,329

Net Loss per Share - Schedule_2

Net Loss per Share - Schedule of Antidilutive Securities Excluded from Calculation of Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - shares	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from calculation of diluted net loss per share	5,928,270	5,213,219
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	5,602,998	3,607,953
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	312,264	1,421,095
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	13,008	184,171