戴纳基美股招股说明书(2026-07-21版)

Our common stock is listed on The Nasdaq Global Select Market under the symbol “DYN.” The last reported sale price ofour common stock on The Nasdaq Global Select Market on July 20, 2026 was $23.45 per share. Investing in our common stock involves a high degree of risk. See “Risk Factors” beginning on pageS-9 of this prospectussupplement and in the documents incorporated by reference into this prospectus supplement. Underwriting discounts and commissions(1) (1)See “Underwriters” beginning on page S-19 for additional information regarding underwriter compensation. We have granted the underwriters an option for a period of 30 days to purchase up to an additional $45,000,000 of shares of ourcommon stock at the public offering price set forth above, less underwriting discounts and commissions. The underwriters expect to deliver the shares of common stock to purchasers on or about July, 2026. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of thesesecurities or passed upon the accuracy or adequacy of this prospectus supplement or the accompanying prospectus. Anyrepresentation to the contrary is a criminal offense. Joint Book-Running Managers The information in this preliminary prospectus supplement is not complete and may be changed. A registration statement relating to these securities has been filed with theSecurities and Exchange Commission and is effective. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell these securities andEvercoreISIRaymondJames Lead ManagerJones July, 2026 Table of Contents TABLE OF CONTENTS Prospectus Prospectus Supplement About This ProspectusWhere You Can Find More InformationIncorporation by ReferenceCautionary Note Regarding Forward-Looking Statements andIndustry DataRisk FactorsAbout Dyne Therapeutics, Inc.Use of ProceedsDescription of Debt SecuritiesDescription of Capital StockDescription of WarrantsDescription of UnitsForms of SecuritiesPlan of DistributionLegal MattersExperts About This Prospectus SupplementCautionary Note Regarding Forward-Looking Statements andIndustry DataProspectus Supplement SummaryRisk FactorsUse of ProceedsDilutionMaterial U.S. Federal Income Tax Considerations ForNon-U.S. Holders of Our Common StockUnderwritersLegal MattersExpertsWhere You Can Find More InformationIncorporation of Certain Information by Reference Table of Contents ABOUT THIS PROSPECTUS SUPPLEMENT This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this offering of common stockand also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference herein. The secondpart, the accompanying prospectus, provides more general information. Generally, when we refer to this prospectus, we are referring to both parts of thisdocument combined. To the extent there is a conflict between the information contained in this prospectus supplement and the information contained inthe accompanying prospectus or any document incorporated by reference therein filed prior to the date of this prospectus supplement, you should rely onthe information in this prospectus supplement; provided that if any statement in one of these documents is inconsistent with a statement in anotherdocument having a later date—for example, a document incorporated by reference in the accompanying prospectus—the statement in the documenthaving the later date modifies or supersedes the earlier statement. We further note that the representations, warranties and covenants made by us in any agreement that is filed as an exhibit to any document that isincorporated by reference herein were made solely for the benefit of the parties to such agreement, including, in some cases, for the purpose ofallocating risk among the parties to such agreements, and should not be deemed to be a representation, warranty or covenant to you. Moreover, suchrepresentations, warranties or covenants were accurate only as of the date when made. Accordingly, such representations, warranties and covenantsshould not be relied on as accurately representing the current state of our affairs. Neither we nor the underwriters have authorized anyone to provide any information other than that contained or incorporated by reference in thisprospectus supplement, the accompanying prospectus or in any free writing prospectus prepared by or on behalf of us or to which we have referred you.We and the underwriters take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you.This prospectus supplement and the accompanying prospectus do not constitute an offer to sell, or a solicitation of an offer to purchase, the securitiesoffered by this prospectus supplement and the accompanying prospectus in any jurisdiction to or from any person to whom or from whom it is unlawfulto ma