Dyne Therapeutics, Inc.

Notes to Condensed Consolidated Financial Statements (Unaudited)

1. Nature of Business and Basis of Presentation

Dyne Therapeutics, Inc. (the “Company”) is a clinical-stage neuromuscular disease company focused on advancing innovative life-transforming therapeutics for people living with genetically driven neuromuscular diseases. The Company was incorporated in Delaware on December 1, 2017 and has a principal place of business in Waltham, Massachusetts.

The Company is subject to risks and uncertainties common to clinical-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for its product candidates, fluctuations in operating results, compliance with government regulations, the ability to establish clinical- and commercial-scale manufacturing processes and the ability to secure additional capital to fund operations. Product candidates and programs currently under development require significant research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s development efforts are successful and product candidates receive regulatory approval, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

The accompanying condensed consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities and commitments in the ordinary course of business. Since inception, the Company has funded its operations with proceeds from the sales of equity securities. The Company expects to continue to generate operating losses for the foreseeable future. The Company expects that its cash, cash equivalents, and marketable securities will be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months from the issuance of these condensed consolidated financial statements.

To continue its development efforts, the Company will need to obtain substantial additional funding through public or private equity offerings, debt financings, collaborations, strategic alliances and/or licensing arrangements in order to fund its research and development and ongoing operating expenses. The Company may not be able to obtain financing on acceptable terms, when needed or at all, and the Company may not be able to enter into collaborations, strategic alliances or licensing arrangements. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. Any collaborations, strategic alliances or licensing arrangements may require the Company to relinquish rights to certain of its technologies, future revenue streams, research programs or product candidates or grant licenses on terms that may not be favorable to the Company. If the Company is unable to obtain funding, the Company could be forced to delay, limit, reduce or eliminate some or all of its research and development programs, pipeline expansion or future commercialization efforts or grant rights to develop and market product candidates, which could adversely affect its business prospects. Although management will continue to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations when needed or at all.

2. Summary of Significant Accounting Policies

The accompanying condensed consolidated financial statements reflect the operations of the Company and the Company’s wholly-owned subsidiary, Dyne Therapeutics Securities Corporation. Intercompany balances and transactions have been eliminated in consolidation. The accompanying condensed consolidated financial statements have been prepared in conformity with generally accepted accounting principles (“GAAP”) in the United States of America. 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 Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).

The financial statements of the Company included herein have been prepared, without audit, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). The unaudited interim financial statements have been prepared on the same basis as audited annual financial statements, except certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. In the opinion of management, the interim financial information reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair representation of the results for the reported periods. Accordingly, these financial statements should be read in conjunction with the financial statements and notes thereto included in the Company’s annual report on Form 10-K filed with the SEC on

February 27, 2025. The results for the three months ended March 31, 2025 are not necessarily indicative of results to be expected for the year ending December 31, 2025, any other interim periods, or any future year or period.

Fair value measurements

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

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Level 1—Unadjusted quoted prices in active markets that are accessible to the reporting entity at the measurement date for identical assets and liabilities.

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Level 2—Inputs other than quoted prices in active markets for identical assets and liabilities that are observable either directly or indirectly for substantially the full term of the asset or liability. Level 2 inputs include the following:

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quoted prices for similar assets and liabilities in active markets;

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quoted prices for identical or similar assets or liabilities in markets that are not active;

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observable inputs other than quoted prices that are used in the valuation of the asset or liabilities (e.g., interest rate and yield curve quotes at commonly quoted intervals); and

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inputs that are derived principally from or corroborated by observable market data by correlation or other means.

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Level 3—Unobservable inputs for the assets or liability (i.e., supported by little or no market activity). Level 3 inputs include management’s own assumptions about the assumptions that market participants would use in pricing the asset or liability (including assumptions about risk).

Net loss per share

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

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

Recently Issued Accounting Pronouncements Not Yet Adopted

In November 2024, the FASB issued ASU 2024-03, Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures (Topic 220-40) ("ASU 2024-03"). The amendments in this update require new disclosures to disaggregate prescribed natural expenses underlying any income statement caption. ASU 2024-03 is effective for annual periods in fiscal years beginning after December 15, 2026, and interim periods thereafter. Early adoption is permitted. ASU 2024-03 applies on a prospective basis for periods beginning after the effective date. However, retrospective application to any or all prior periods presented is permitted. We are currently assessing the impact ASU 2024-03 will have on the condensed consolidated financial statements and disclosures.

In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740) ("ASU 2023-09"). The amendments in this update require enhanced annual income tax disclosures for the effective tax rate reconciliation and income taxes paid. The amendments are effective for public business entities for annual periods beginning after December 15, 2024 and for annual periods beginning after December 15, 2025 for all other entities. Early adoption is permitted for annual financial statements that have not yet been issued or made available for issuance. ASU 2023-09 applies on a prospective basis to annual financial statements for periods beginning after the effective date. However, retrospective application in all prior periods presented is permitted. The Company is assessing what impact ASU 2023-09 will have on the condensed consolidated financial statements and disclosures.

3. Cash, Cash Equivalents and Restricted Cash

Cash includes cash in readily available checking accounts and cash equivalents include money market funds that invest in U.S. treasury securities and all highly liquid investments maturing within 90 days from the date of purchase.

Amounts included in restricted cash represent amounts pledged as collateral for letters of credit required for security deposits on the Company’s leased facilities.

Cash, cash equivalents and restricted cash consisted of the following:

4. Fair Value Measurements

The following tables set forth marketable securities for the periods presented:

The following tables set forth by level, within the fair value hierarchy (see Note 2), the assets carried at fair value on a recurring basis for the periods presented:

The fair value of U.S. government treasury notes and money market funds were determined by the Company based on quoted market prices, which represent a Level 1 measurement within the fair value hierarchy. Commercial paper, certificates of deposit, and corporate debt securities were valued by the Company using quoted prices in active markets for similar securities, which represent a Level 2 measurement within the fair value hierarchy.

There wereno transfers between Level 1, Level 2, or Level 3 during the periods presented.

The following table summarizes the scheduled maturity for the Company's marketable securities for the periods presented:

Financial instruments not recorded at fair value

The carrying values of cash, cash equivalents, accounts payable and accrued expenses that are reported on the balance sheets approximate their fair value due to the short-term nature of these assets and liabilities.

5. Property and Equipment

Property and equipment consisted of the following:

Depreciation expense for the three months ended March 31, 2025 was $0.5 million. Depreciation expense for thethree months ended March 31, 2024 was $0.4 million.

6. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:

7. Stockholders' Equity

Common Stock

In November 2021, the Company filed a universal shelf registration statement on Form S-3 (the "2021 Shelf Registration Statement"), to register for sale from time to time up to $400.0 million of common stock, preferred stock, debt securities, warrants and/or units in one or more offerings. Further, in November 2021, the Company entered into an Open Market Sale Agreement (the "Sales Agreement") with Jefferies LLC ("Jefferies") as the Company's sales agent, and included in the 2021 Shelf Registration Statement a prospectus relating to the Sales Agreement pursuant to which, from time to time, the Company could offer and sell shares of its common stock having an aggregate offering price of up to $150.0 million in an "at-the-market" offering program. On January 4, 2024, the Company notified Jefferies that it was suspending and terminating the prospectus filed under the 2021 Shelf Registration Statement relating to the Sales Agreement for the Company's "at-the-market" offering program.

On March 5, 2024, the Company filed a universal shelf registration statement on Form S-3, (the “2024 Shelf Registration Statement”), and included a prospectus relating to the Sales Agreement. Under the 2024 Shelf Registration Statement, the Company may offer and sell debt securities, common stock, preferred stock, units and/or warrants from time to time at an indeterminate aggregate offering price in one or more offerings. In November 2024, the Company filed a prospectus supplement relating to the Sales Agreement, pursuant to which, in accordance with the Sales Agreement, the Company may offer and sell shares of its common stock having an aggregate offering price of up to $300.0 million in an “at-the-market” offering.

During the three months ended March 31, 2025, the Company issued and sold an aggregate of 10,660,159 shares of common stock pursuant to the Sales Agreement for aggregate net proceeds of $140.6 million, after deducting commissions and offering expenses payable by the Company. The Company sold such shares at a weighted average price of $13.60 per share.

Atlas Venture and related affiliated entities were beneficial owners of approximately 8.0% of the Company's outstanding common stock as of March 31, 2025. The chairman of the Company's board of directors is a partner at Atlas Venture. On January 27, 2025, the Company issued and sold 1,111,111 sharesof common stock through its at-the-market offering program that Atlas Venture and related affiliated entities purchased at a purchase price of $13.50 per share for aggregate gross proceeds of $15.0 million. The shares were purchased at the prevailing market price.

2020 Stock Incentive Plan

In August 2020 the Company’s board of directors adopted and the Company’s stockholders approved the 2020 Stock Incentive Plan, (the "2020 Plan"), which became effective on September 16, 2020. The 2020 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards to employees, directors, consultants and advisors of the Company. The 2020 Plan is administered by the Company’s board of directors or by a committee appointed by the board of directors. Upon the effectiveness of the 2020 Plan, the Company ceased granting awards under the 2018 Stock Incentive Plan. The number of shares initially reserved for issuance under the 2020 Plan was 4,884,233. The number of shares of common stock reserved for issuance under the 2020 Plan may automatically increase on the first day of each fiscal year, beginning with the fiscal year commencing on January 1, 2021 and continuing for each fiscal year until, and including the fiscal year commencing on, January 1, 2030, in an amount equal to the lower of (1)5% of the shares of common stock outstanding on such date and (2) an amount determined by the Company’s board of directors. On January 1, 2025,5,115,931 shares were added to the shares reserved for issuance under the 2020 Plan in the fifth of these annual increases.

As of March 31, 2025,6,989,676 shares remained available for future issuance under the 2020 Plan.

2020 Employee Stock Purchase Plan

In August 2020 the Company’s board of directors adopted and the Company’s stockholders approved the 2020 Employee Stock Purchase Plan (the “2020 ESPP”), which became effective September 16, 2020. The 2020 ESPP is administered by the Company’s board of directors or by a committee appointed by the board of directors. The 2020 ESPP initially provides participating employees with the opportunity to purchase up to an aggregate of 488,414 shares of common stock. The number of shares of common stock reserved for issuance under the 2020 ESPP may automatically increase on the first day of each fiscal year, beginning with the fiscal year commencing on January 1, 2021 and continuing for each fiscal year until, and including the fiscal year commencing on, January 1, 2030, in an amount equal to the least of (1)1,953,656 shares of common stock, (2)1% of the shares of common stock outstanding on such date, and (3) an amount determined by the board of directors.

As of March 31, 2025, no offering periods have commenced under the 2020 ESPP and 488,414 shares remained available for issuance.

2024 Inducement Stock Incentive Plan

In March 2024, the Company's board of directors adopted the 2024 Inducement Stock Incentive Plan (the "2024 Inducement Plan"). The 2024 Inducement Plan provides for the grant of nonstatutory stock options, stock appreciation rights, restricted stock, restricted stock units and other stock-based awards with respect to an aggregate of 900,000 shares of Common Stock (subject to adjustment as provided in the 2024 Inducement Plan). Awards under the 2024 Inducement Plan may only be granted to new employees who were not previously an employee or director of the Company or are commencing employment with the Company following a bona fide period of non-employment, in either case, as an inducement material to the individual’s entering into employment with the Company and in accordance with the requirements of Nasdaq Stock Market Rule 5635(c)(4). In February 2025, the Company's board of directors approved an additional 1,000,000 shares for issuance under the 2024 Inducement Plan.

During the three months ended March 31, 2025, the Company granted inducement equity awards to its new chief financial officer as a material inducement to the acceptance of his employment consisting of stock options to purchase up to 214,500 shares of the Company’s common stock and restricted stock units with respect to 66,100 shares of the Company’s common stock. As of March 31, 2025,939,547 shares remained available for future issuance under the 2024 Inducement Plan. In April 2025, the Company granted inducement equity awards to three new employees as a material inducement to acceptance of their respective employment consisting of stock options to purchase up to an aggregate of 330,200 shares of the Company’s common stock and restricted stock units with respect to an aggregate of 101,900 shares of the Company’s common stock.

Stock option valuation

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

The assumptions that the Company used to determine the grant-date fair value of options granted were as follows:

Stock option activity

A summary of the Company’s stock option activity and related information for thethree months ended March 31, 2025 is as follows:

The intrinsic value of options exercised for the three months ended March 31, 2025 and 2024 totaled $0.9 million and $32.5 million, respectively. The weighted-average grant date fair value of the options granted during thethree months ended March 31, 2025 and 2024 was $7.69 per share and $16.06 per share, respectively. As of March 31, 2025 there was $67.4 million of unrecognized compensation expense, which the Company expects to recognize over a weighted-average period of 2.9 years.

Effective January 2025, the Company entered into a consulting agreement with its former chief medical officer resulting in the modification of previously issued stock option awards. The modification resulted in $0.9 million of additional stock-based compensation expense, all of which was recognized during the quarter ended March 31, 2025. The expense was recorded within research and development expenses on the condensed consolidated statements of operations and comprehensive loss. Based on the terms of the consulting agreement, options to purchase 58,659 shares of common stock were forfeited in January 2025.

Restricted stock units

A restricted stock unit (“RSU”) represents the right to receiveone share of common stock upon vesting of the RSU. The Company grants RSUs with service conditions that vest infour equal annual installments provided that the employee remains employed with the Company, RSUs with service conditions that vest in sixteen equal quarterly installments provided that the employee remains employed with the Company and RSUs with performance-based vesting conditions. As of March 31, 2025, there are no RSUs with performance-based vesting conditions outstanding. Thefair value of each

RSUis based on the closing price of the Company’s common stock on the date of grant. A summary of the Company’s RSU activity and related information for thethree months ended March 31, 2025 is as follows:

The fair value of RSUs vested during the three months ended March 31, 2025 and 2024 totaled $7.0 million and $5.9 million, respectively. The weighted average grant date fair value of RSUs granted during the three months ended March 31, 2024 was $21.77 per share. As of March 31, 2025, there was $60.9 million of unrecognized compensation costs ​​​​​​​related to unvested RSUs, which are expected to be recognized over a weighted-average period of 3.0 years.

Effective January 2025, the Company entered into a consulting agreement with its former chief medical officer resulting in the modification of previously issued restricted stock unit awards. The modification resulted in the recognition of $0.3 million of additional stock-based compensation expense, all of which was recognized during the quarter ended March 31, 2025. The expense was recorded within research and development expenses on the condensed consolidated statements of operations and comprehensive loss. Based on the terms of the consulting agreement,76,662 restricted stock units were forfeited in January 2025.

The Company recorded stock-based compensation expense in the following expense categories of its condensed consolidated statements of operations and comprehensive loss:

8. Segment Reporting

The Company’s segment determination is based on the financial results that are regularly evaluated by the Company’s chief operating decision maker ("CODM") to determine resource allocation and assess performance. The Company's CODM is its chief executive officer. The Company hasone operating and one reportable segment. Net long-lived assets are all physically located in the United States and the total assets of the segment equal the total assets presented on the condensed consolidated balance sheet. The primary financial measure by which the CODM evaluates the business is net loss. The CODM uses net loss to monitor budget versus actual results to assess performance of the segment. A summary of the significant segment expenses reported to the CODM are shown below for thethree months ended March 31, 2025 and 2024: