Praxis Precision Medicines (PRAX) 10-Q 11 May 21 2021 Q1 Quarterly report Financial data

Cover Page

Cover Page - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity File Number	001-39620
Entity Registrant Name	PRAXIS PRECISION MEDICINES, INC.
Entity Central Index Key	0001689548
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-5195942
Entity Address, Address Line One	One Broadway
Entity Address, Address Line Two	16th Floor
Entity Address, Postal Zip Code	02142
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
City Area Code	617
Local Phone Number	300-8460
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	PRAX
Security Exchange Name	NASDAQ
Amendment Flag	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		38,664,518

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 131,152	$ 296,608
Marketable securities	139,659	0
Prepaid expenses and other current assets	7,753	5,718
Total current assets	278,564	302,326
Property and equipment, net	109	82
Operating lease right-of-use assets	571	754
Other non-current assets	9	15
Total assets	279,253	303,177
Current liabilities:
Accounts payable	5,774	4,088
Accrued expenses	7,386	10,869
Operating lease liabilities	578	763
Total current liabilities	13,738	15,720
Total liabilities	13,738	15,720
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000,000 shares authorized and no shares issued or outstanding as of March 31, 2021 and December 31, 2020	0	0
Common stock, $0.0001 par value; 150,000,000 shares authorized; 38,621,049 shares issued and outstanding as of March 31, 2021, and 38,268,543 shares issued and outstanding as of December 31, 2020	4	4
Additional paid-in capital	442,524	437,007
Accumulated other comprehensive loss	(86)	0
Accumulated deficit	(176,927)	(149,554)
Total stockholders’ equity	265,515	287,457
Total liabilities and stockholders’ equity	$ 279,253	$ 303,177

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, authorized (in shares)	10,000,000	10,000,000
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, authorized (in shares)	150,000,000	150,000,000
Common stock, issued (in shares)	38,621,049	38,268,543
Common stock, outstanding (in shares)	38,621,049	38,268,543

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating expenses:
Research and development	$ 17,929	$ 6,868
General and administrative	9,490	1,601
Total operating expenses	27,419	8,469
Loss from operations	(27,419)	(8,469)
Other income:
Interest income, net	46	128
Total other income	46	128
Loss before benefit from income taxes	(27,373)	(8,341)
Benefit from income taxes	0	11
Net loss	(27,373)	(8,330)
Accretion and cumulative dividends on redeemable convertible preferred stock	0	(2,064)
Gain on repurchase of redeemable convertible preferred stock	0	493
Net loss attributable to common stockholders	$ (27,373)	$ (9,901)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.71)	$ (6.08)
Weighted average common shares outstanding, basic and diluted (in shares)	38,470,710	1,629,340

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net loss and comprehensive loss	$ (27,373)	$ (8,330)
Unrealized losses on marketable securities, net of tax	(86)	0
Comprehensive Income (Loss)	$ (27,459)	$ (8,330)

Consolidated Statements of Rede

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Series A Redeemable Convertible Preferred Stock	Series B Redeemable Convertible Preferred Stock	Series B-1 Redeemable Convertible Preferred Stock	Series C Redeemable Convertible Preferred Stock	Series C Redeemable Convertible Preferred StockAccumulated Deficit
Beginning balance, Shares at Dec. 31, 2019						8,075,799	14,913,704	2,666,666	9,805,827
Beginning balance at Dec. 31, 2019						$ 9,932	$ 49,969	$ 10,431	$ 50,789
Increase (Decrease) in Temporary Equity [Roll Forward]
Repurchase of Series C redeemable convertible preferred stock (in shares)									(5,825,243)
Repurchase of Series C redeemable convertible preferred stock									$ (30,493)
Series C redeemable convertible preferred stock issuance costs									37
Accretion of redeemable convertible preferred stock to redemption value						$ 160	$ 890	$ 199	$ 815
Ending balance, shares at Mar. 31, 2020						8,075,799	14,913,704	2,666,666	3,980,584
Ending balance at Mar. 31, 2020						$ 10,092	$ 50,859	$ 10,630	$ 21,074
Beginning balance, Shares at Dec. 31, 2019		1,621,880
Beginning balance at Dec. 31, 2019	$ (81,008)	$ 1	$ 0	$ (81,009)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of Series C redeemable convertible preferred stock									$ 493	$ 493
Stock-based compensation expense	147		147
Vesting of restricted common stock awards (in shares)		13,143
Accretion of redeemable convertible preferred stock to redemption value	(2,064)		(147)	(1,917)
Net loss and comprehensive loss	(8,330)			(8,330)
Ending balance, shares at Mar. 31, 2020		1,635,023
Ending balance at Mar. 31, 2020	$ (90,762)	$ 1	0	(90,763)	0
Beginning balance, Shares at Dec. 31, 2020						0	0	0	0
Beginning balance at Dec. 31, 2020						$ 0	$ 0	$ 0	$ 0
Ending balance, shares at Mar. 31, 2021						0	0	0	0
Ending balance at Mar. 31, 2021						$ 0	$ 0	$ 0	$ 0
Beginning balance, Shares at Dec. 31, 2020	38,268,543	38,268,543
Beginning balance at Dec. 31, 2020	$ 287,457	$ 4	437,007	(149,554)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	$ 4,666		4,666
Issuance of common stock upon exercise of stock options (in shares)	352,506	352,506
Issuance of common stock upon exercise of stock options	$ 851		851
Unrealized losses on marketable securities, net of tax	(86)				(86)
Net loss and comprehensive loss	$ (27,373)			(27,373)	0
Ending balance, shares at Mar. 31, 2021	38,621,049	38,621,049
Ending balance at Mar. 31, 2021	$ 265,515	$ 4	$ 442,524	$ (176,927)	$ (86)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net loss	$ (27,373)	$ (8,330)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	23	10
Stock-based compensation expense	4,666	147
Non-cash operating lease expense	183	169
Amortization of premiums and discounts on marketable securities, net	261	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,035)	(294)
Accounts payable	2,208	991
Accrued expenses	(3,477)	(1,097)
Operating lease liabilities	(185)	(169)
Other	7	4
Net cash used in operating activities	(25,722)	(8,569)
Cash flows from investing activities:
Purchases of property and equipment	(4)	0
Purchases of marketable securities	140,006	0
Net cash used in investing activities	(140,010)	0
Cash flows from financing activities:
Payment of deferred offering costs	(575)	0
Proceeds from exercise of options to purchase common stock	851	0
Repurchase of Series C redeemable convertible preferred stock	0	(30,000)
Net cash provided by (used in) financing activities	276	(30,000)
Decrease in cash, cash equivalents and restricted cash	(165,456)	(38,569)
Cash, cash equivalents and restricted cash, beginning of period	297,208	45,415
Cash, cash equivalents and restricted cash, end of period	131,752	6,846
Reconciliation of cash, cash equivalents and restricted cash:
Total cash, cash equivalents and restricted cash	131,752	6,846
Supplemental disclosures of non-cash activities:
Purchases of property, plant and equipment included in accounts payable	51	0
Accretion of redeemable convertible preferred stock to redemption value	0	2,064
Redeemable convertible preferred stock issuance costs included in accounts payable	$ 0	$ 36

Nature of the Business

Nature of the Business	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the Business	Nature of the Business Praxis Precision Medicines, Inc. (“Praxis” or the “Company”) is a clinical-stage biopharmaceutical company translating genetic insights into the development of therapies for central nervous system (“CNS”) disorders characterized by neuronal imbalance. The Company has established a broad portfolio, including multiple disclosed programs across CNS disorders, including depression, epilepsy, movement disorders and pain syndromes, with three clinical-stage product candidates. The Company intends to develop differentiated therapies that can deliver long-term benefits to human health by meaningfully impacting patients and society. The Company’s most advanced programs, PRAX-114 and PRAX-944, are currently in Phase 2/3 and Phase 2 development, respectively. PRAX-114 is an extrasynaptic GABA A receptor preferring positive allosteric modulator currently being developed for the treatment of major depressive disorder and perimenopausal depression. The Company plans to initiate Phase 2 trials of PRAX-114 in post-traumatic stress disorder and essential tremor ("ET") in the second half of 2021. PRAX-944 is a selective small molecule inhibitor of T-type calcium channels currently being developed for the treatment of ET. The Company plans to initiate a Phase 2 trial of PRAX-944 in Parkinson's disease in the first half of 2022. Praxis was incorporated in 2015 and commenced operations in 2016. The Company has funded its operations primarily with proceeds from the issuance of convertible debt, Series A redeemable convertible preferred stock (the “Series A Preferred Stock”), Series B redeemable convertible preferred stock (the “Series B Preferred Stock”), Series B-1 redeemable convertible preferred stock (the “Series B-1 Preferred Stock”), Series C redeemable convertible preferred stock (the “Series C Preferred Stock”) and Series C-1 redeemable convertible preferred stock (the "Series "C-1 Preferred Stock" and together the Series A Preferred Stock, Series B Preferred Stock, Series B-1 Preferred Stock, Series C Preferred Stock and Series C-1 Preferred Stock are collectively referred to as the “Redeemable Convertible Preferred Stock”), and from proceeds from its initial public offering ("IPO"). From inception through March 31, 2021, the Company raised $411.0 million in aggregate cash proceeds from these transactions, net of issuance costs. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including but not limited to, risks associated with completing preclinical studies and clinical trials, receiving regulatory approvals for product candidates, development by competitors of new biopharmaceutical products, dependence on key personnel, protection of proprietary technology, compliance with government regulations and the ability to secure additional capital to fund operations. Programs currently under development will require significant additional research and development efforts, including preclinical and clinical testing and regulatory approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize revenue from product sales. Liquidity In accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40) , 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 that these condensed consolidated financial statements are issued. The Company has incurred recurring losses since its inception, including net losses of $27.4 million for the three months ended March 31, 2021. In addition, as of March 31, 2021, the Company had an accumulated deficit of $176.9 million. The Company expects to continue to generate operating losses for the foreseeable future. The Company expects that its cash, cash equivalents and marketable securities as of March 31, 2021 of $270.8 million will be sufficient to fund the operating expenses and capital expenditure requirements necessary to advance its research efforts and clinical trials for at least one year from the date of issuance of these condensed consolidated financial statements. The future viability of the Company is dependent on its ability to raise additional

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying condensed consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and ASUs of the FASB. The significant accounting policies used in preparation of these condensed consolidated financial statements for the three months ended March 31, 2021 are consistent with those discussed in Note 2 to the consolidated financial statements included in the Company's 2020 Annual Report on Form 10-K, except as noted immediately below. Unaudited Interim Condensed Consolidated Financial Information The accompanying condensed consolidated balance sheet as of March 31, 2021, the condensed consolidated statements of operations for the three months ended March 31, 2021 and 2020, the condensed consolidated statements of comprehensive loss for the three months ended March 31, 2021 and 2020, the condensed consolidated statements of cash flows for the three months ended March 31, 2021 and 2020 and the condensed consolidated statements of redeemable convertible preferred stock and stockholders’ equity (deficit) for the three months ended March 31, 2021 and 2020 are unaudited. The unaudited interim financial statements have been prepared on the same basis as the audited annual consolidated financial statements, and in the opinion of management reflect all adjustments, which include only normal recurring adjustments necessary for the fair statement of the Company’s financial position as of March 31, 2021, the results of its operations for the three months ended March 31, 2021 and 2020 and its cash flows for the three months ended March 31, 2021 and 2020. Financial statement disclosures for the three months ended March 31, 2021 and 2020 are condensed and do not include all disclosures required for an annual set of financial statements in accordance with GAAP. The results for the three months ended March 31, 2021 are not necessarily indicative of results to be expected for the year ended December 31, 2021, any other interim periods, or any future year or period. Use of Estimates The preparation of condensed consolidated financial statements in conformity with GAAP requires management to make estimates 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, the accrual for research and development expenses, stock-based compensation expense, and the valuation of equity awards. 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 materially from those estimates. Marketable Securities The Company invests its excess cash in money market funds and debt instruments of the U.S. Treasury, financial institutions, corporations and U.S. government agencies with strong credit ratings and an investment grade rating at or above A-1 or P-1 by two of the three nationally recognized statistical rating organizations. The Company has established guidelines relative to diversification and maturities that maintain safety and liquidity, and periodically reviews and modifies these guidelines to maximize trends in yields and interest rates without compromising safety and liquidity. The Company classifies its investments in debt instruments as available-for-sale. Available-for-sale investments are reported at fair value at each balance sheet date, and include any unrealized holding gains and losses in accumulated other comprehensive gain (loss), a component of stockholders’ equity. Realized gains and losses are included in the Company's condensed consolidated statements of operations. All of the Company's available-for-sale securities are available for use in its current operations. As a result, the Company has categorized all of these securities as current assets even though the stated maturity of some individual securities may be one year or more beyond the balance sheet date. The Company evaluates securities for impairment at the end of each reporting period. Impairment is evaluated considering numerous factors, and their relative significance varies depending on the situation. Factors considered include whether a decline in fair value below the amortized cost basis is due to credit-related factors or non-credit-related factors, the financial condition and near-term prospects of the issuer, and the Company's intent and ability to hold the investment to allow for an anticipated recovery in fair value. A credit-related impairment is recognized as an allowance on the balance sheet with a corresponding adjustment to earnings. Any impairment that is not credit- related is recognized in other comprehensive (loss) income, net of applicable taxes. Recent Accounting Pronouncements Recently Adopted Accounting Pronouncements In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740)—Simplifying the Accounting for Income Taxes ("ASU 2019-12"). The ASU simplifies the accounting for income taxes by eliminating certain exceptions to the guidance in ASC 740, Income Taxes, related to the approach for allocating income tax expense or benefit for the year to continuing operations, discontinued operations, other comprehensive income, and other charges or credits recorded directly to shareholders’ equity; the methodology for calculating income taxes in an interim period; and the recognition of deferred tax liabilities for outside basis differences. On January 1, 2021, the Company early adopted ASU 2019-12 on a prospective basis, with no material impact on its condensed consolidated financial statements and related disclosures. Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326)—Measurement of Credit Losses on Financial Instruments, which has been subsequently amended by ASU No. 2018-19, ASU No. 2019-04, ASU No. 2019-05, ASU No. 2019-10, ASU No. 2019-11 and ASU No. 2020-03 (“ASU 2016-13”). The provisions of ASU 2016-13 modify the impairment model to utilize an expected loss methodology in place of the currently used incurred loss methodology and require a consideration of a broader range of reasonable and supportable information to inform credit loss estimates. ASU 2016-13 is effective for the Company on January 1, 2023, with early adoption permitted. The Company is currently evaluating the potential impact that this standard may have on its financial position and results of operations, as well as the timing of its adoption of this standard.

Marketable Securities

Marketable Securities	3 Months Ended
	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	Marketable Securities The following is a summary of the Company's investment portfolio at March 31, 2021 (in thousands). The Company did not have any marketable securities as of December 31, 2020. Gross Unrealized Estimated Cost Gains Losses Fair Value Available-for-sale securities: Commercial paper $ 55,926 $ — $ — $ 55,926 Corporate debt securities 44,686 — (40) 44,646 Total securities with a maturity of one year or less $ 100,612 $ — $ (40) $ 100,572 Corporate debt securities 26,888 — (46) 26,842 Debt securities issued by U.S. government agencies 12,245 — — 12,245 Total securities with a maturity of one to two years $ 39,133 $ — $ (46) $ 39,087 Total available-for-sale securities $ 139,745 $ — $ (86) $ 139,659

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair value is defined as the price that would be received to sell an asset in an orderly transaction between market participants at the measurement date. The Company categorizes financial assets measured at fair value based on a fair value hierarchy. The following fair value hierarchy is used to classify financial assets based on observable inputs and unobservable inputs used to value the financial assets: • Level 1: Unadjusted quoted prices in active markets that are accessible at the measurement date for identical assets; • Level 2: Quoted prices for similar assets in active markets, quoted prices in markets that are not active, or inputs which are unobservable, either directly or indirectly, for substantially the full term of the asset; or • Level 3: Prices or valuation techniques that require inputs that are both significant to the valuation of the asset and unobservable. The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicates the level of the fair value hierarchy utilized to determine such fair values (in thousands): As of March 31, 2021 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 127,773 $ — $ — $ 127,773 Marketable securities: Corporate debt securities — 71,488 — 71,488 Commercial paper — 55,926 — 55,926 U.S. government agency and treasury securities 12,245 — — 12,245 $ 140,018 $ 127,414 $ — $ 267,432 As of December 31, 2020 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 290,931 $ — $ — $ 290,931 $ 290,931 $ — $ — $ 290,931

Accrued Expenses

Accrued Expenses	3 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
Accrued Expenses	Accrued ExpensesAccrued expenses consisted of the following (in thousands): March 31, 2021 December 31, 2020 Accrued external research and development expenses $ 4,541 $ 4,206 Accrued personnel-related expenses 1,281 5,516 Accrued consulting expenses 822 220 Accrued other 742 927 Total accrued expenses $ 7,386 $ 10,869

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and ContingenciesIn October 2018, the Company entered into a sublease agreement for office space located in Cambridge, Massachusetts that expires on December 30, 2021, with no option to renew or terminate early. The base rent increases by approximately 1% annually. The Company issued a letter of credit to the landlord related to the security deposit, secured by restricted cash, which is reflected within prepaid expenses and other current assets on the accompanying condensed consolidated balance sheets as of March 31, 2021 and December 31, 2020, as the lease term expires less than twelve months from the condensed consolidated balance sheet dates. This lease qualifies as an operating lease.

Common Stock and Preferred Stoc

Common Stock and Preferred Stock	3 Months Ended
	Mar. 31, 2021
Stockholders' Equity Note [Abstract]
Common Stock and Preferred Stock	Common Stock and Preferred Stock Common Stock As of March 31, 2021 and December 31, 2020, the authorized capital stock of the Company included 150,000,000 shares of common stock, $0.0001 par value. As of March 31, 2021 and December 31, 2020, the Company did not hold any treasury shares. Shares Reserved for Future Issuance The Company has reserved the following shares of common stock for future issuance: March 31, December 31, Shares reserved for exercise of outstanding stock options 6,648,367 5,944,546 Shares reserved for future awards under the 2020 Stock Option and Incentive Plan 3,515,208 3,036,776 Shares reserved for future awards under the 2020 Employee Stock Purchase Plan 654,204 327,102 Shares reserved for vesting of restricted stock units 328,363 — Total shares of authorized common stock reserved for future issuance 11,146,142 9,308,424 Preferred Stock As of March 31, 2021 and December 31, 2020, the authorized capital stock of the Company included 10,000,000 shares of undesignated preferred stock, $0.0001 par value.

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	Stock-Based Compensation 2020 Stock Option and Incentive Plan The total number of shares of common stock authorized for issuance under the 2020 Stock Option Incentive Plan (the "2020 Plan”) as of March 31, 2021 and December 31, 2020 was 5,184,455 shares and 3,271,028 shares, respectively. 2017 Stock Incentive Plan The total number of shares of common stock authorized for issuance under the 2017 Stock Incentive Plan (the "2017 Plan”) as of March 31, 2021 and December 31, 2020 was 5,937,763 shares. Any authorization to issue new options under the 2017 Plan was cancelled upon the effectiveness of the 2020 Plan and no further awards will be granted under the 2017 Plan. 2020 Employee Stock Purchase Plan The total number of shares of common stock authorized for issuance under the 2020 Employee Stock Purchase Plan (the "2020 ESPP”) as of March 31, 2021 and December 31, 2020 was 654,204 shares and 327,102 shares, respectively. Restricted Stock Units The following table summarizes the Company’s restricted stock unit activity: Shares Weighted Unvested as of December 31, 2020 — $ — Issued 329,963 52.16 Vested — — Forfeited (1,600) 52.53 Unvested as of March 31, 2021 328,363 $ 52.16 Stock Options The following table summarizes the Company’s stock option activity: Number of Weighted Weighted Aggregate (In years) (In thousands) Outstanding as of December 31, 2020 5,944,546 $ 7.47 Granted 1,139,723 52.60 Exercised (352,506) 2.42 $ 16,671 Cancelled or Forfeited (83,396) 20.14 Outstanding as of March 31, 2021 6,648,367 $ 15.31 9.10 $ 140,012 Exercisable as of March 31, 2021 792,732 $ 2.48 7.48 $ 24,004 Vested and expected to vest as of March 31, 2021 6,498,698 $ 15.49 9.16 $ 136,220 The aggregate intrinsic value of stock options outstanding, exercisable, and vested and expected to vest is calculated as the difference between the exercise price of the underlying stock options and the estimated fair value of the Company’s common stock for those stock options that had exercise prices lower than the estimated fair value of the Company’s common stock at March 31, 2021. The aggregate intrinsic value of stock options exercised is calculated as the difference between the exercise price of the underlying stock options and the estimated fair value of the Company’s common stock on the date of exercise for those stock options that had exercise prices lower than the estimated fair value of the Company’s common stock on the exercise date. Stock Option Valuation The weighted-average assumptions that the Company used in the Black-Scholes option pricing model to determine the grant-date fair value of stock options granted to employees and non-employees on the date of grant were as follows: Three Months Ended March 31, 2021 Risk-free interest rate 0.66 % Expected term (in years) 6.14 Expected volatility 85.28 % Expected dividend yield — % The weighted-average grant-date fair value of the Company’s stock options granted during the three months ended March 31, 2021 was $37.54 per share. There were no stock options granted during the three months ended March 31, 2020. Stock-Based Compensation Stock-based compensation expense was allocated as follows (in thousands): Three Months Ended 2021 2020 Research and development $ 2,318 $ 102 General and administrative 2,348 45 Total stock-based compensation expense $ 4,666 $ 147 As of March 31, 2021, total unrecognized compensation expense related to unvested stock-based awards was $81.2 million, which is expected to be recognized over a weighted-average period of 3.30 years.

Net Loss per Share

Net Loss per Share	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Net Loss per Share	Net Loss per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share data): Three Months Ended 2021 2020 Numerator: Net loss $ (27,373) $ (8,330) Accretion and cumulative dividends on redeemable convertible preferred stock — (2,064) Gain on repurchase of redeemable convertible preferred stock — 493 Net loss attributable to common stockholders $ (27,373) $ (9,901) Denominator: Weighted average common shares outstanding, basic and diluted 38,470,710 1,629,340 Net loss per share attributable to common stockholders, basic and diluted $ (0.71) $ (6.08) The following potential shares of common stock, 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 been anti-dilutive: Three Months Ended 2021 2020 Outstanding stock options 6,648,367 1,634,686 Unvested restricted common stock and restricted stock units 328,363 35,047 Series A Preferred Stock — 3,773,820 Series B Preferred Stock — 6,969,173 Series B-1 Preferred Stock — 1,246,133 Series C Preferred Stock — 1,860,126 6,976,730 15,518,985 The shares of common stock issuable upon conversion of the Redeemable Convertible Preferred Stock for the three months ended March 31, 2020 assumed automatic conversion in the event of a qualified public offering.

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2021
Related Party Transactions [Abstract]
Related Party Transactions	Related Party TransactionsOn September 11, 2019, the Company entered into a Cooperation and License Agreement (the “License Agreement”) with RogCon Inc. (“RogCon”). Under the License Agreement, RogCon granted to the Company an exclusive, worldwide license under RogCon’s intellectual property to research, develop and commercialize products for the treatment of all forms of epilepsy and/or neurodevelopmental disorders in each case caused by any mutation of the SCN2A gene. Pursuant to the terms of the License Agreement, the Company will conduct, at its own cost and expense, the research and development activities assigned to it under the associated research plan. In addition, the Company is responsible for reimbursing RogCon for any costs associated with research and development activities RogCon performs at the request of the Company. One of the founders of RogCon became the Company’s General Counsel in June 2020. The Company continues to reimburse RogCon for its out-of-pocket costs incurred for activities performed under the License Agreement. During both the three months ended March 31, 2021 and 2020, the Company expensed less than $0.1 million for the reimbursement of RogCon’s out-of-pocket costs. As of March 31, 2021, the Company had accrued expenses of $0.3 million due to RogCon under the License Agreement.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	11. Subsequent EventsThe Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the condensed consolidated financial statements to provide additional evidence for certain estimates or to identify matters that require additional disclosure. The Company has concluded that no subsequent events have occurred that require disclosure

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and ASUs of the FASB. The significant accounting policies used in preparation of these condensed consolidated financial statements for the three months ended March 31, 2021 are consistent with those discussed in Note 2 to the consolidated financial statements included in the Company's 2020 Annual Report on Form 10-K, except as noted immediately below.
Unaudited Interim Condensed Consolidated Financial Information	Unaudited Interim Condensed Consolidated Financial Information The accompanying condensed consolidated balance sheet as of March 31, 2021, the condensed consolidated statements of operations for the three months ended March 31, 2021 and 2020, the condensed consolidated statements of comprehensive loss for the three months ended March 31, 2021 and 2020, the condensed consolidated statements of cash flows for the three months ended March 31, 2021 and 2020 and the condensed consolidated statements of redeemable convertible preferred stock and stockholders’ equity (deficit) for the three months ended March 31, 2021 and 2020 are unaudited. The unaudited interim financial statements have been prepared on the same basis as the audited annual consolidated financial statements, and in the opinion of management reflect all adjustments, which include only normal recurring adjustments necessary for the fair statement of the Company’s financial position as of March 31, 2021, the results of its operations for the three months ended March 31, 2021 and 2020 and its cash flows for the three months ended March 31, 2021 and 2020. Financial statement disclosures for the three months ended March 31, 2021 and 2020 are condensed and do not include all disclosures required for an annual set of financial statements in accordance with GAAP. The results for the three months ended March 31, 2021 are not necessarily indicative of results to be expected for the year ended December 31, 2021, any other interim periods, or any future year or period.
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with GAAP requires management to make estimates 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, the accrual for research and development expenses, stock-based compensation expense, and the valuation of equity awards. 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 materially from those estimates.
Marketable Securities	Marketable Securities The Company invests its excess cash in money market funds and debt instruments of the U.S. Treasury, financial institutions, corporations and U.S. government agencies with strong credit ratings and an investment grade rating at or above A-1 or P-1 by two of the three nationally recognized statistical rating organizations. The Company has established guidelines relative to diversification and maturities that maintain safety and liquidity, and periodically reviews and modifies these guidelines to maximize trends in yields and interest rates without compromising safety and liquidity. The Company classifies its investments in debt instruments as available-for-sale. Available-for-sale investments are reported at fair value at each balance sheet date, and include any unrealized holding gains and losses in accumulated other comprehensive gain (loss), a component of stockholders’ equity. Realized gains and losses are included in the Company's condensed consolidated statements of operations. All of the Company's available-for-sale securities are available for use in its current operations. As a result, the Company has categorized all of these securities as current assets even though the stated maturity of some individual securities may be one year or more beyond the balance sheet date. The Company evaluates securities for impairment at the end of each reporting period. Impairment is evaluated considering numerous factors, and their relative significance varies depending on the situation. Factors considered include whether a decline in fair value below the amortized cost basis is due to credit-related factors or non-credit-related factors, the financial condition and near-term prospects of the issuer, and the Company's intent and ability to hold the investment to allow for an anticipated recovery in fair value. A credit-related impairment is recognized as an allowance on the balance sheet with a corresponding adjustment to earnings. Any impairment that is not credit- related is recognized in other comprehensive (loss) income, net of applicable taxes.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326)—Measurement of Credit Losses on Financial Instruments, which has been subsequently amended by ASU No. 2018-19, ASU No. 2019-04, ASU No. 2019-05, ASU No. 2019-10, ASU No. 2019-11 and ASU No. 2020-03 (“ASU 2016-13”). The provisions of ASU 2016-13 modify the impairment model to utilize an expected loss methodology in place of the currently used incurred loss methodology and require a consideration of a broader range of reasonable and supportable information to inform credit loss estimates. ASU 2016-13 is effective for the Company on January 1, 2023, with early adoption permitted. The Company is currently evaluating the potential impact that this standard may have on its financial position and results of operations, as well as the timing of its adoption of this standard.

Marketable Securities (Tables)

Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Debt Securities, Available-for-sale	The following is a summary of the Company's investment portfolio at March 31, 2021 (in thousands). The Company did not have any marketable securities as of December 31, 2020. Gross Unrealized Estimated Cost Gains Losses Fair Value Available-for-sale securities: Commercial paper $ 55,926 $ — $ — $ 55,926 Corporate debt securities 44,686 — (40) 44,646 Total securities with a maturity of one year or less $ 100,612 $ — $ (40) $ 100,572 Corporate debt securities 26,888 — (46) 26,842 Debt securities issued by U.S. government agencies 12,245 — — 12,245 Total securities with a maturity of one to two years $ 39,133 $ — $ (46) $ 39,087 Total available-for-sale securities $ 139,745 $ — $ (86) $ 139,659

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Summary of financial assets measured at fair value on a recurring basis	The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicates the level of the fair value hierarchy utilized to determine such fair values (in thousands): As of March 31, 2021 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 127,773 $ — $ — $ 127,773 Marketable securities: Corporate debt securities — 71,488 — 71,488 Commercial paper — 55,926 — 55,926 U.S. government agency and treasury securities 12,245 — — 12,245 $ 140,018 $ 127,414 $ — $ 267,432 As of December 31, 2020 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 290,931 $ — $ — $ 290,931 $ 290,931 $ — $ — $ 290,931

Accrued Expenses (Tables)

Accrued Expenses (Tables)	3 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
Schedule of Accrued Liabilities [Table Text Block]	Accrued expenses consisted of the following (in thousands): March 31, 2021 December 31, 2020 Accrued external research and development expenses $ 4,541 $ 4,206 Accrued personnel-related expenses 1,281 5,516 Accrued consulting expenses 822 220 Accrued other 742 927 Total accrued expenses $ 7,386 $ 10,869

Common Stock and Preferred St_2

Common Stock and Preferred Stock (Tables)	3 Months Ended
	Mar. 31, 2021
Stockholders' Equity Note [Abstract]
Summary of common stock reserved for future issuance	The Company has reserved the following shares of common stock for future issuance: March 31, December 31, Shares reserved for exercise of outstanding stock options 6,648,367 5,944,546 Shares reserved for future awards under the 2020 Stock Option and Incentive Plan 3,515,208 3,036,776 Shares reserved for future awards under the 2020 Employee Stock Purchase Plan 654,204 327,102 Shares reserved for vesting of restricted stock units 328,363 — Total shares of authorized common stock reserved for future issuance 11,146,142 9,308,424

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Summary of restricted stock activity	The following table summarizes the Company’s restricted stock unit activity: Shares Weighted Unvested as of December 31, 2020 — $ — Issued 329,963 52.16 Vested — — Forfeited (1,600) 52.53 Unvested as of March 31, 2021 328,363 $ 52.16
Summary of stock option activity	The following table summarizes the Company’s stock option activity: Number of Weighted Weighted Aggregate (In years) (In thousands) Outstanding as of December 31, 2020 5,944,546 $ 7.47 Granted 1,139,723 52.60 Exercised (352,506) 2.42 $ 16,671 Cancelled or Forfeited (83,396) 20.14 Outstanding as of March 31, 2021 6,648,367 $ 15.31 9.10 $ 140,012 Exercisable as of March 31, 2021 792,732 $ 2.48 7.48 $ 24,004 Vested and expected to vest as of March 31, 2021 6,498,698 $ 15.49 9.16 $ 136,220
Schedule of fair value of stock option awards on the grant date using the Black-Scholes option valuation model	The weighted-average assumptions that the Company used in the Black-Scholes option pricing model to determine the grant-date fair value of stock options granted to employees and non-employees on the date of grant were as follows: Three Months Ended March 31, 2021 Risk-free interest rate 0.66 % Expected term (in years) 6.14 Expected volatility 85.28 % Expected dividend yield — %
Summary of stock-based compensation expense	Stock-based compensation expense was allocated as follows (in thousands): Three Months Ended 2021 2020 Research and development $ 2,318 $ 102 General and administrative 2,348 45 Total stock-based compensation expense $ 4,666 $ 147

Net Loss per Share (Tables)

Net Loss per Share (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Summary of basic and diluted net loss per share attributable to common stockholders	Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share data): Three Months Ended 2021 2020 Numerator: Net loss $ (27,373) $ (8,330) Accretion and cumulative dividends on redeemable convertible preferred stock — (2,064) Gain on repurchase of redeemable convertible preferred stock — 493 Net loss attributable to common stockholders $ (27,373) $ (9,901) Denominator: Weighted average common shares outstanding, basic and diluted 38,470,710 1,629,340 Net loss per share attributable to common stockholders, basic and diluted $ (0.71) $ (6.08)
Summary of antidilutive securities excluded from computation of earnings per share	The following potential shares of common stock, 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 been anti-dilutive: Three Months Ended 2021 2020 Outstanding stock options 6,648,367 1,634,686 Unvested restricted common stock and restricted stock units 328,363 35,047 Series A Preferred Stock — 3,773,820 Series B Preferred Stock — 6,969,173 Series B-1 Preferred Stock — 1,246,133 Series C Preferred Stock — 1,860,126 6,976,730 15,518,985

Nature of the Business - Additi

Nature of the Business - Additional Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)product	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of product candidates | product	3
Proceeds from issuance or sale of equity	$ 411,000
Net loss	27,373	$ 8,330
Accumulated deficit	176,927		$ 149,554
Cash, cash equivalents, and short-term investments	$ 270,800

Marketable Securities (Details)

Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Cost, Maturity of one year or less	$ 100,612
Available-for-Sale, Cost, Maturity of one to two years	39,133
Available-for-sale, Cost	139,745
Available-for-Sale, Gross Unrealized Gain, Maturity of one year or less	0
Available-for-Sale, Gross Unrealized Gain, Maturity of one to two years	0
Available-for-sale, Gross Unrealized Gain	0
Available-for-Sale, Gross Unrealized Loss, Maturity of one year or less	(40)
Available-for-Sale, Gross Unrealized Loss, Maturity of one to two years	(46)
Available-for-sale, Gross Unrealized Loss	(86)
Marketable securities	100,572
Available-for-Sale, Estimated Fair Value, Maturity of one to two years	39,087
Available-for-sale, Estimated Fair Value	139,659	$ 0
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Cost, Maturity of one year or less	55,926
Available-for-Sale, Gross Unrealized Gain, Maturity of one year or less	0
Available-for-Sale, Gross Unrealized Loss, Maturity of one year or less	0
Marketable securities	55,926
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Cost, Maturity of one year or less	44,686
Available-for-Sale, Cost, Maturity of one to two years	26,888
Available-for-Sale, Gross Unrealized Gain, Maturity of one year or less	0
Available-for-Sale, Gross Unrealized Gain, Maturity of one to two years	0
Available-for-Sale, Gross Unrealized Loss, Maturity of one year or less	(40)
Available-for-Sale, Gross Unrealized Loss, Maturity of one to two years	(46)
Marketable securities	44,646
Available-for-Sale, Estimated Fair Value, Maturity of one to two years	26,842
Debt securities issued by U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Available-for-Sale, Cost, Maturity of one to two years	12,245
Available-for-Sale, Gross Unrealized Gain, Maturity of one to two years	0
Available-for-Sale, Gross Unrealized Loss, Maturity of one to two years	0
Available-for-Sale, Estimated Fair Value, Maturity of one to two years	$ 12,245

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 267,432	$ 290,931
Fair Value, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	140,018	290,931
Fair Value, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	127,414	0
Fair Value, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	127,773	290,931
Money market funds | Fair Value, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	127,773	290,931
Money market funds | Fair Value, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	0	0
Money market funds | Fair Value, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents	0	$ 0
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	71,488
Corporate debt securities | Fair Value, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0
Corporate debt securities | Fair Value, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	71,488
Corporate debt securities | Fair Value, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0
U.S. government agency and treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	12,245
U.S. government agency and treasury securities | Fair Value, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	12,245
U.S. government agency and treasury securities | Fair Value, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0
U.S. government agency and treasury securities | Fair Value, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	55,926
Commercial paper | Fair Value, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0
Commercial paper | Fair Value, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	55,926
Commercial paper | Fair Value, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	$ 0

Accrued Expenses - Summary of A

Accrued Expenses - Summary of Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Accrued external research and development expenses	$ 4,541	$ 4,206
Accrued personnel-related expenses	1,281	5,516
Accrued consulting expenses	822	220
Accrued other	742	927
Total accrued expenses	$ 7,386	$ 10,869

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	Mar. 31, 2021
Office Space in Cambridge Massachusetts
Loss Contingencies [Line Items]
Percentage Increase In Annual Base Rent	1.00%

Common Stock and Preferred St_3

Common Stock and Preferred Stock - Summary of Common Stock Reserved For Future Issuance (Details) - shares	Mar. 31, 2021	Dec. 31, 2020
Schedule Of Common Stock Reserved For Future Issuance [Line Items]
Common stock reserved for future issuance (in shares)	11,146,142	9,308,424
Share-based Payment Arrangement | Shares reserved for future awards under the 2020 Stock Option and Incentive Plan
Schedule Of Common Stock Reserved For Future Issuance [Line Items]
Common stock reserved for future issuance (in shares)	3,515,208	3,036,776
Share-based Payment Arrangement | Shares reserved for future awards under the 2020 Employee Stock Purchase Plan
Schedule Of Common Stock Reserved For Future Issuance [Line Items]
Common stock reserved for future issuance (in shares)	654,204	327,102
Restricted Stock
Schedule Of Common Stock Reserved For Future Issuance [Line Items]
Common stock reserved for future issuance (in shares)	328,363	0
Share-based Payment Arrangement, Option
Schedule Of Common Stock Reserved For Future Issuance [Line Items]
Common stock reserved for future issuance (in shares)	6,648,367	5,944,546

Common Stock and Preferred St_4

Common Stock and Preferred Stock - Additional Information (Details) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
Schedule Of Common Stock Reserved For Future Issuance [Abstract]
Common stock, authorized (in shares)	150,000,000	150,000,000
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Treasury shares	0	0
Preferred stock, authorized (in shares)	10,000,000	10,000,000
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value of stock options granted, Per share	$ 37.54
Unrecognized compensation expense related to unvested stock based awards	$ 81.2
Unrecognized compensation expense expected to be recognised	3 years 3 months 18 days
Two Thousand Twenty Employee Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	5,184,455	3,271,028
2017 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	5,937,763	5,937,763
Two Thousand Twenty Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	654,204	327,102

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Restricted Stock Activity (Details) - Restricted Stock	3 Months Ended
	Mar. 31, 2021$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares) | shares	0
Issued (in shares) | shares	329,963
Vested (in shares) | shares	0
Forfeited (in shares) | shares	(1,600)
Ending balance (in shares) | shares	328,363
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Unvested beginning balance (in dollars per share) | $ / shares	$ 0
Issued (in dollars per share) | $ / shares	52.16
Vested (in dollars per share) | $ / shares	0
Forfeitures (in dollars per shares) | $ / shares	52.53
Unvested ending balance (in dollars per share) | $ / shares	$ 52.16

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares) | shares	5,944,546
Granted (in shares) | shares	1,139,723
Exercised (in shares) | shares	(352,506)
Canceled or forfeited (in shares) | shares	(83,396)
Ending balance (in shares) | shares	6,648,367
Number of shares exercisable (in shares) | shares	792,732
Vested and expected to vest (in shares) | shares	6,498,698
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Beginning balance (in dollars per share) | $ / shares	$ 7.47
Granted (in dollars per share) | $ / shares	52.60
Exercised (in dollars per share) | $ / shares	2.42
Cancelled or forfeited (in dollars per share) | $ / shares	20.14
Ending balance (in dollars per share) | $ / shares	15.31
Exercisable (in dollars per share) | $ / shares	2.48
Vested and expected to vest (in dollars per share) | $ / shares	$ 15.49
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted average remaining contractual term outstanding	9 years 1 month 6 days
Weighted average remaining contractual term exercisable	7 years 5 months 23 days
Weighted average remaining contractual term vested and expected to vest	9 years 1 month 28 days
Aggregate intrinsic value exercised | $	$ 16,671
Aggregate intrinsic value outstanding | $	140,012
Aggregate intrinsic value exercisable | $	24,004
Aggregate intrinsic value vested and expected to vest | $	$ 136,220

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Fair Value of Stock Option Awards on the Grant Date Using the Black-Scholes Option Valuation Model (Details)	3 Months Ended
	Mar. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Risk-free interest rate	0.66%
Expected term (in years)	6 years 1 month 20 days
Expected volatility	85.28%
Expected dividend yield	0.00%

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 4,666	$ 147
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	2,318	102
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 2,348	$ 45

Net Loss per Share - Summary of

Net Loss per Share - Summary of basic and diluted net loss per share attributable to common stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Numerator:
Net loss and comprehensive loss	$ (27,373)	$ (8,330)
Accretion and cumulative dividends on redeemable convertible preferred stock	0	(2,064)
Gain on repurchase of redeemable convertible preferred stock	0	493
Net loss attributable to common stockholders	$ (27,373)	$ (9,901)
Denominator:
Weighted average common shares outstanding, basic and diluted (in shares)	38,470,710	1,629,340
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.71)	$ (6.08)

Net Loss per Share - Summary _2

Net Loss per Share - Summary of antidilutive securities excluded from computation of earnings per share (Details) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	6,976,730	15,518,985
Employee Stock Option
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	6,648,367	1,634,686
Restricted Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	328,363	35,047
Series A Preferred Stock | Convertible Preferred Stocks
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	3,773,820
Series B Preferred Stock | Convertible Preferred Stocks
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	6,969,173
Series B-1 Preferred Stock | Convertible Preferred Stocks
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	1,246,133
Series C Preferred Stock | Convertible Preferred Stocks
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	1,860,126

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - RogCon Inc. - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Related Party Transaction [Line Items]
Due to related parties	$ 0.3
Expense Reimbursement
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	$ 0.1	$ 0.1

Uncategorized Items - prax-2021

Label	Element	Value
Restricted Cash	us-gaap_RestrictedCash	$ 600,000
Restricted Cash	us-gaap_RestrictedCash	$ 600,000