Common Stock, $0.001 par value per share

Wave Life Sciences, Inc.

733 Concord Avenue, Cambridge, MA, 02138

This Schedule 13D/A is being filed on behalf of RA Capital Management, L.P. ("RA Capital"), Peter Kolchinsky, Rajeev Shah, and RA Capital Healthcare Fund, L.P. (the "Fund"), who are collectively referred to herein as the "Reporting Persons." The agreement among the Reporting Persons to file this 13D/A jointly in accordance with Rule 13d-1(k) of the Act, is attached hereto as Exhibit 99.1. The Reporting Persons' beneficial ownership of the Issuer's securities consists of (i) 26,975,505 shares of common stock directly held by the Fund; (ii) 7,093,656 shares of common stock issuable upon exercise of pre-funded warrants ("Pre-Funded Warrants") directly held by the Fund, which are immediately exercisable in full as of the date hereof; and (iii) 28,815 shares of common stock and vested options (right to buy) to purchase 216,430 shares of common stock held by Dr. Kolchinsky for the benefit of RA Capital. RA Capital Healthcare Fund GP, LLC is the general partner of the Fund. The general partner of RA Capital is RA Capital Management GP, LLC, of which Dr. Kolchinsky and Mr. Shah are the controlling persons. RA Capital serves as investment adviser for the Fund and may be deemed a beneficial owner, for purposes of Section 13(d) of the Act, of any securities of the Issuer held by the Fund. The Fund has delegated to RA Capital the sole power to vote and the sole power to dispose of all securities held in its portfolio, including the shares of the Issuer's common stock reported herein. Because the Fund has divested itself of voting and investment power over the reported securities it holds and may not revoke that delegation on less than 61 days' notice, the Fund disclaims beneficial ownership of the securities it holds for purposes of Section 13(d) of the Act and therefore disclaims any obligation to report ownership of the reported securities under Section 13(d) of the Act. As managers of RA Capital, Dr. Kolchinsky and Mr. Shah may be deemed beneficial owners, for purposes of Section 13(d) of the Act, of any securities of the Issuer beneficially owned by RA Capital. RA Capital, Dr. Kolchinsky, and Mr. Shah disclaim beneficial ownership of the securities reported in this Schedule 13D/A other than for the purpose of determining their obligations under Section 13(d) of the Act, and the filing of this Schedule 13D/A shall not be deemed an admission that either RA Capital, Dr. Kolchinsky, or Mr. Shah is the beneficial owner of such securities for any other purpose.

The address of the principal business office of each of the Reporting Persons is 200 Berkeley Street, 18th Floor, Boston, MA 02116.

The Fund is a private investment vehicle. RA Capital provides investment management services to the Fund. The principal occupation of each of Dr. Kolchinsky and Mr. Shah is investment management.

During the last five years, none of the Reporting Persons has been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree of final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

See Item 6 of the cover pages.

Rows 11 and 13 of each Reporting Person's cover page to this 13D/A set forth the aggregate number of shares of common stock and percentages of shares of common stock beneficially owned by such Reporting Person and are incorporated by reference. The percentage set forth in each row 13 is based upon the sum of (i) 197,048,175 shares of common stock outstanding as of July 23, 2026, as reported in the Issuer's Quarterly Report on Form 10-Q filed with the SEC on July 30, 2026 and (ii) 12,700 shares of common stock issued upon the vesting of restricted stock units held by Dr. Kolchinsky on August 11, 2026, and giving effect to stock options and Pre-Funded Warrants, to the extent exercisable within 60 days hereof, as referenced herein.

Rows 7 through 10 of each Reporting Person's cover page to this 13D/A set forth the number of shares of common stock as to which such Reporting Person has the sole or shared power to vote or direct the vote and sole or shared power to dispose or to direct the disposition and are incorporated by reference.

Except as set forth below, none of the Reporting Persons has effected any transactions with respect to the securities of the Issuer during the past sixty days. Reporting No. Price Per Transaction Person Date Shares Share Vest Stock Option (Right to Buy) RA Capital 08/11/2026 76,200 (1) Vest Restricted Stock Units RA Capital 08/11/2026 12,700 (2) (1) This option represents a right to purchase a total of 76,200 shares of the Issuer's common stock, which vested in full on August 11, 2026. These options have an exercise price of $8.11. (2) The restricted stock units vested in full on August 11, 2026.

No person (other than the Reporting Persons) is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the shares of common stock subject to this 13D/A.

Not applicable.