Amendment: SEC Form SCHEDULE 13D/A filed by Solid Biosciences Inc.

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 Nexus Fund and the Account. 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 convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).

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.

Item 3 of the Statement is hereby amended and supplemented as follows: February 2026 Open Market Purchase On February 6, 2026, the Fund purchased an aggregate of 354,936 shares of common stock in open market transactions at purchase prices ranging from $6.36 to $6.63 per share (weighted average purchase price of $6.49 per share). The aggregate purchase price of such shares was $2,304,350.99, which was funded by the working capital of the Fund. March 2026 Securities Purchase Agreement On March 6, 2026, the Issuer entered into a securities purchase agreement with certain institutional accredited investors (the "March 2026 PIPE Investors"), including the Fund, pursuant to which the Issuer issued and sold to the March 2026 PIPE Investors in a private placement (the "March 2026 Private Placement") (i) an aggregate of 14,973,257 shares of common stock (the "Shares") at a price of $5.61 per share; and (ii) an aggregate of 27,807,482 warrants (the "March 2026 Pre-Funded Warrants") in lieu of shares of common stock, at a purchase price of $5.609 per March 2026 Pre-Funded Warrant. The March 2026 Private Placement closed on March 9, 2026. The Fund purchased 4,456,327 March 2026 Pre-Funded Warrants in the March 2026 Private Placement, for total consideration of $24,995,538, which was funded by the working capital of the Fund.

Rows 11 and 13 of each Reporting Person's cover page to this Schedule 13D/A set forth the aggregate number of shares of common stock and percentages of the 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) 77,910,239 shares of common stock outstanding as of October 29, 2025, as reported in the Issuer's Quarterly Report on Form 10-Q filed with the SEC on November 3, 2025; (ii) 14,973,257 shares issued in the March 2026 Private Placement; and (iii) shares issuable upon exercise of the Pre-Funded Warrants held by the Fund, to the extent exercisable within 60 days hereof, as referenced herein. Due to field limitations of the EDGAR filing system, the percentages listed in Row 13 of each of the cover pages for RA Capital, Dr. Kolchinsky and Mr. Shah have been rounded down to 9.9%.

Rows 7 through 10 of each Reporting Person's cover page to this Schedule 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 herein, none of the Reporting Persons has effected any transactions with respect to the securities of the Issuer during the past sixty days.

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 securities subject to this Schedule 13D/A.

Not applicable.

Item 6 of the Statement is hereby amended and supplemented as follows: March 2026 Pre-Funded Warrants Each March 2026 Pre-Funded Warrant has an exercise price of $0.001 per share of common stock, is immediately exercisable and does not expire. Under the terms of the March 2026 Pre-Funded Warrants, the Issuer may not effect the exercise of any March 2026 Pre-Funded Warrant, and the Fund will not be entitled to exercise any portion of any March 2026 Pre-Funded Warrant, which, upon giving effect to such exercise, would cause the Fund (together with its affiliates) to own more than 9.99% of the number of shares of the common stock outstanding immediately after giving effect to such exercise, as such percentage ownership is determined in accordance with the terms of the March 2026 Pre-Funded Warrants. The exercise price and the number of shares of common stock issuable upon exercise of each March 2026 Pre-Funded Warrant are subject to appropriate adjustment in the event of certain stock dividends and distributions, stock splits, stock combinations, reclassifications or similar events affecting the common stock. In the event of certain fundamental transactions (as described in the March 2026 Pre-Funded Warrants), a holder of March 2026 Pre-Funded Warrants will be entitled to receive, upon exercise of the March 2026 Pre-Funded Warrants, the kind and amount of securities, cash or property that such holder would have received had they exercised in full the March 2026 Pre-Funded Warrants immediately prior to such fundamental transaction without regard to any limitations on exercise contained in the March 2026 Pre-Funded Warrants. References to and the description of the March 2026 Pre-Funded Warrants set forth above in this Item 6 do not purport to be complete and are qualified in their entirety by reference to the full text of the Form of Pre-Funded Warrant, which is filed herewith as Exhibit 99.2 and incorporated by reference herein. Registration Rights Agreement Also on March 6, 2026, the Issuer entered into a registration rights agreement (the "March 2026 Registration Rights Agreement") with the March 2026 PIPE Investors, pursuant to which the Issuer agreed to register for resale the Shares and the shares of the Issuer's common stock issuable upon exercise of the March 2026 Pre-Funded Warrants (collectively, the "Registrable Securities"). Under the March 2026 Registration Rights Agreement, the Issuer has agreed to file a registration statement covering the resale by the March 2026 PIPE Investors of their Registrable Securities no later than 30 days following the closing of the March 2026 Private Placement. The Issuer has agreed to use reasonable best efforts to cause such registration statement to be declared effective as soon as reasonably practicable and to keep such registration statement effective until the date that all Registrable Securities covered by such registration statement have been sold or can be sold without restriction pursuant to Rule 144 and without the requirement to be in compliance with Rule 144(c)(1) (or any successor thereof) promulgated under the Securities Act of 1933, as amended. The Issuer has agreed to be responsible for all fees and expenses incurred in connection with the registration of the Registrable Securities. The Issuer has granted the March 2026 PIPE Investors customary indemnification rights in connection with the registration statement. The March 2026 PIPE Investors have also granted the Issuer customary indemnification rights in connection with the registration statement. References to and the description of the March 2026 Registration Rights Agreement set forth above in this Item 6 do not purport to be complete and are qualified in their entirety by reference to the full text of the Form of Registration Rights Agreement, which is filed herewith as Exhibit 99.3 and incorporated by reference herein.

Exhibit 99.1 Joint Filing Agreement (incorporated by reference to Exhibit 99.1 to the Reporting Persons' Schedule 13D/A filed with the SEC on February 21, 2025). Exhibit 99.2 Form of Pre-Funded Warrant (incorporated by reference to Exhibit 4.1 to the Issuer's Current Report on Form 8-K (File No. 1-38360) filed on March 6, 2026). Exhibit 99.3 Form of Registration Rights Agreement (incorporated by reference to Exhibit 10.2 to the Issuer's Current Report on Form 8-K (File No. 1-38360) filed on March 6, 2026).