RA Capital Discloses ~9.9% Stake in Solid Biosciences (SLDB) After Purchases

RA Capital and affiliated persons report owning 7,997,510 shares of Solid Biosciences (SLDB), representing approximately 9.9% of the outstanding common stock.

Accepted by SEC EDGAR 08/14/2025 - 06:06 PM EDT Learn about SEC filing dates

Rhea-AI Filing Summary

RA Capital and affiliated persons report owning 7,997,510 shares of Solid Biosciences (SLDB), representing approximately 9.9% of the outstanding common stock. The reported position includes 5,673,193 shares directly held by RA Capital Healthcare Fund, L.P., additional small direct holdings through related accounts and pre-funded warrants exercisable for up to 3,722,085 shares subject to a beneficial ownership blocker that prevents exercise above 9.99% ownership. Recent open-market purchases disclosed include 529,768 shares at a weighted-average of $4.49 and smaller buys at prices between $3.80 and $4.50 per share. RA Capital, Peter Kolchinsky and Rajeev Shah disclose shared voting and dispositive power over the reported shares and state delegations of voting/dispositive authority from certain funds.

Positive

• Significant stake disclosed: Aggregate beneficial ownership of 7,997,510 shares (~9.9%) is material relative to total outstanding shares.
• Active accumulation: Recent open-market purchases including 529,768 shares at a weighted-average $4.49 show deliberate buying activity.
• Transparency on holdings: Filing discloses composition of holdings (funds, nexus fund, account, pre-funded warrants) and voting/dispositive arrangements.

Negative

• Exercise constraint: Pre-Funded Warrants contain a Beneficial Ownership Blocker preventing exercise above 9.99%, limiting immediate dilution or increased ownership via warrants.
• Delegations and disclaimers: Several entities disclaim beneficial ownership due to delegated authority, which may complicate clear attribution of control for some investors.

Insights

Securities Analyst

TL;DR: RA Capital and affiliates hold a near-10% economic stake in SLDB, with recent open-market accumulation and warrants constrained by an ownership blocker.

This Schedule 13D/A discloses an aggregate position of 7,997,510 shares (9.9%), combining direct holdings and pre-funded warrants subject to a blocker that limits exercise above 9.99%. The filing details meaningful open-market purchases, notably 529,768 shares at a weighted-average $4.49, indicating active accumulation at mid-single-digit dollar prices. Reporting persons claim shared voting/dispositive power and note delegations from certain funds, which affects who is deemed the beneficial owner for reporting purposes. For investors, the position size is material relative to outstanding shares and could influence liquidity and shareholder dynamics.

Corporate Governance Expert

TL;DR: The disclosure signals coordinated ownership and delegated voting arrangements, with a blocker limiting warrant exercise above 9.99%.

The filing highlights joint reporting among RA Capital, its principals, and investment vehicles, and explains that some funds have delegated sole voting and dispositive authority to the adviser. Such delegations, and the express disclaimers of beneficial ownership by certain funds, clarify control relationships for regulatory purposes. The existence of a Beneficial Ownership Blocker in the pre-funded warrants constrains immediate increases in exercisable shares and preserves a sub-10% ownership threshold, which is material to governance and potential filing obligations.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

How many shares of Solid Biosciences (SLDB) do RA Capital and affiliates report owning?

They report owning 7,997,510 shares of common stock, representing approximately 9.9% of outstanding shares.

Do RA Capital’s holdings include warrants or only common stock?

Yes; the position includes pre-funded warrants exercisable for up to 3,722,085 shares, subject to a Beneficial Ownership Blocker.

What recent purchases did the filing disclose for SLDB?

Recent open-market buys include 529,768 shares at a weighted-average $4.49 plus smaller purchases between $3.80 and $4.50 per share.

Who has voting and dispositive power over the reported SLDB shares?

RA Capital states it has or may be deemed to have shared voting and dispositive power; certain funds delegated sole power to RA Capital, which reported shared power by principals.

Does the Beneficial Ownership Blocker affect the ability to increase the stake?

Yes; the blocker prevents exercising pre-funded warrants to the extent exercise would result in ownership above 9.99%.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 10)

SOLID BIOSCIENCES INC.

(Name of Issuer)

Common Stock, $0.001 par value per share

(Title of Class of Securities)

83422E204

(CUSIP Number)

Peter Kolchinsky
RA Capital Management, L.P., 200 Berkeley Street, 18th Floor
Boston, MA, 02116
617.778.2500

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

08/12/2025

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

SCHEDULE 13D

CUSIP No. 83422E204

1

Name of reporting person

RA Capital Management, L.P.

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 7,997,510.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 7,997,510.00

11

Aggregate amount beneficially owned by each reporting person

7,997,510.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

9.9 %

14

Type of Reporting Person (See Instructions)

IA, PN

SCHEDULE 13D

CUSIP No. 83422E204

1

Name of reporting person

Peter Kolchinsky

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 7,997,510.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 7,997,510.00

11

Aggregate amount beneficially owned by each reporting person

7,997,510.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

9.9 %

14

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13D

CUSIP No. 83422E204

1

Name of reporting person

Rajeev Shah

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 7,997,510.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 7,997,510.00

11

Aggregate amount beneficially owned by each reporting person

7,997,510.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

9.9 %

14

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13D

CUSIP No. 83422E204

1

Name of reporting person

RA Capital Healthcare Fund, L.P.

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 7,859,280.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 7,859,280.00

11

Aggregate amount beneficially owned by each reporting person

7,859,280.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

9.8 %

14

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Common Stock, $0.001 par value per share
(b)	Name of Issuer: SOLID BIOSCIENCES INC.
(c)	Address of Issuer's Principal Executive Offices: 500 Rutherford Avenue, Third Floor, Charlestown, MASSACHUSETTS , 02129.
Item 1 Comment: This Amendment No. 10 (this "Amendment No. 10" or this "Schedule 13D/A") amends and supplements the statement on Schedule 13D originally filed with the Securities and Exchange Commission (the "SEC") on February 9, 2018, and amended on July 30, 2019, December 16, 2020, March 23, 2021, September 6, 2022, October 4, 2022, December 5, 2022, January 11, 2024, June 12, 2024 and February 21, 2025 (as amended, the "Statement") by the Reporting Persons. Unless otherwise defined herein, capitalized terms used in this Amendment No. 10 shall have the meanings ascribed to them in the Statement. Unless amended or supplemented below, the information in the Statement remains unchanged.
Item 2.	Identity and Background
(a)	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"). RA Capital, Dr. Kolchinsky, Mr. Shah and the Fund are collectively referred to herein as the "Reporting Persons." The agreement among the Reporting Persons to file this Schedule 13D/A jointly in accordance with Rule 13d-1(k) of the Securities Exchange Act of 1934, as amended, (the "Act") is attached hereto as Exhibit 99.1. The Reporting Persons' beneficial ownership of the Issuer's common stock consists of (i) 5,673,193 shares of Common Stock directly held by the Fund; (ii) 109,661 shares of common stock directly held by the RA Capital Nexus Fund, L.P. (the "Nexus Fund"); (iii) 28,569 shares of common stock directly held by a separately managed account (the "Account"); and (iv) pre-funded warrants ("Pre-Funded Warrants") exercisable for up to 3,722,085 shares of common stock directly held by the Fund. The Pre-Funded Warrants contain a provision (the "Beneficial Ownership Blocker"), which precludes the exercise of the Pre-Funded Warrants to the extent that, following exercise, the Fund, together with its affiliates and other attribution parties, would own more than 9.99% of the common stock outstanding. The Fund is currently prohibited from exercising the Pre-Funded Warrants to the extent that such exercise would result in beneficial ownership of more than 7,997,510 shares of common stock. RA Capital Healthcare Fund GP, LLC is the general partner of the Fund and RA Capital Nexus Fund GP, LLC is the general partner of the Nexus 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 each of the Fund, the Nexus Fund and the Account 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 Nexus Fund or the Account. Each of the Fund and the Nexus 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 each of the Fund and the Nexus 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, each of the Fund and the Nexus 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.
(b)	The address of the principal business office of each of the Reporting Persons is 200 Berkeley Street, 18th Floor, Boston, MA 02116.
(c)	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.
(d)	During the last five years, none of the Reporting Persons has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).
(e)	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.
(f)	See Item 6 of the cover pages.
Item 3.	Source and Amount of Funds or Other Consideration
	Item 3 of the Statement is hereby amended and supplemented as follows: On June 16, 2025, the Fund purchased 18,917 shares of common stock in open market transactions at prices ranging from $3.80 to $4.43 per share (a weighted-average price of $4.31 per share). On June 18, 2025, the Fund purchased 2,125 shares of common stock in open market transactions at $4.50 per share. On June 23, 2025, the Fund purchased 529,768 shares of common stock in open market transactions at prices ranging from $4.41 to $4.50 per share (a weighted-average price of $4.49 per share). On June 26, 2025, the Fund purchased 2,125 shares of common stock in open market transactions at $4.50 per share. On July 1, 2025, the Fund purchased 100 shares of common stock in open market transactions at $4.50 per share.
Item 5.	Interest in Securities of the Issuer
(a)	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) 77,869,071 shares of common stock outstanding as of August 7, 2025, as reported in the Issuer's Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission (the "SEC") on August 12, 2025; and (ii) 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%.
(b)	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.
(c)	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.
(d)	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.
(e)	Not applicable.
Item 7.	Material to be Filed as Exhibits.
	Exhibit 99.1 Joint Filing Agreement (incorporated by reference to Exhibit 99.1 to the Reporting Persons' Schedule 13D 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 February 18, 2025).

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

RA Capital Management, L.P.

Signature:	/s/ Peter Kolchinsky
Name/Title:	By Peter Kolchinsky, Authorized Signatory
Date:	08/14/2025

Peter Kolchinsky

Signature:	/s/ Peter Kolchinsky
Name/Title:	Peter Kolchinsky
Date:	08/14/2025

Rajeev Shah

Signature:	/s/ Rajeev Shah
Name/Title:	Rajeev Shah
Date:	08/14/2025

RA Capital Healthcare Fund, L.P.

Signature:	/s/ Peter Kolchinsky
Name/Title:	By RA Capital Healthcare Fund GP, LLC, its General Partner, By Peter Kolchinsky, Manager
Date:	08/14/2025