RA Capital (NASDAQ: SLDB) boosts Solid Biosciences holding to 11.9% ownership

Rhea-AI Filing Summary

RA Capital Management and affiliates report an updated stake in Solid Biosciences Inc., now beneficially owning 12,036,126 shares of common stock, or 11.9% of the company. Most of this is held through RA Capital Healthcare Fund, which directly owns 11,897,896 shares.

The position also includes pre-funded warrants exercisable for up to 8,178,412 additional shares, but a Beneficial Ownership Blocker prevents exercises that would lift the Fund’s holdings above 9.99% of Solid’s outstanding common stock. RA Capital serves as investment adviser to all reporting vehicles, while Kolchinsky and Shah are managers of RA Capital.

On June 18, 2026, the Fund bought 338,100 shares in open-market trades at prices between $8.25 and $8.35, with a weighted-average of $8.30 per share. On June 22, 2026, it purchased an additional 2,358,048 shares at $8.20 per share in an at-the-market offering by Solid Biosciences, all funded from the Fund’s working capital. Ownership percentages are calculated using 98,449,606 shares outstanding as of May 8, 2026, plus the 2,358,048 new ATM shares issued to the Fund.

Insights

Equity ownership and governance analyst

RA Capital modestly increases its already large stake in Solid Biosciences.

RA Capital and related entities now report beneficial ownership of 12,036,126 Solid Biosciences shares, or 11.9% of the company. The position is primarily held in RA Capital Healthcare Fund, with RA Capital acting as investment adviser across the pooled vehicles and managed account.

The filing details fresh buying: on June 18, 2026 the Fund acquired 338,100 shares in the open market around $8.30 per share, then on June 22, 2026 it bought 2,358,048 shares at $8.20 in an at-the-market issuance by Solid. These are cash purchases funded from the Fund’s working capital.

The disclosure also highlights pre-funded warrants exercisable for up to 8,178,412 shares, constrained by a Beneficial Ownership Blocker that caps the Fund at 9.99% direct ownership. Actual impact on Solid’s share dynamics will depend on any future warrant exercises and additional transactions, which would appear in subsequent ownership updates.

Key Figures

RA Capital beneficial ownership: 12,036,126 shares Ownership percentage: 11.9% Fund direct holdings: 11,897,896 shares +5 more

8 metrics

RA Capital beneficial ownership 12,036,126 shares Aggregate common stock beneficially owned, representing 11.9% of class

Ownership percentage 11.9% Percent of Solid Biosciences common stock represented by 12,036,126 shares

Fund direct holdings 11,897,896 shares Common stock directly held by RA Capital Healthcare Fund, 11.8% of class

Pre-funded warrants size 8,178,412 shares Maximum SLDB shares issuable upon exercise of pre-funded warrants held by the Fund

Open-market purchase 338,100 shares at ~$8.30 June 18, 2026 purchases, prices $8.25–$8.35, weighted-average $8.30

ATM offering purchase 2,358,048 shares at $8.20 June 22, 2026 purchase by the Fund in issuer’s at-the-market offering

Shares outstanding baseline 98,449,606 shares Solid Biosciences common stock outstanding as of May 8, 2026 from Form 10-Q

Beneficial Ownership Blocker limit 9.99% Cap on direct ownership for pre-funded warrant exercises by the Fund

Key Terms

Schedule 13D/A, pre-funded warrants, Beneficial Ownership Blocker, at-the-market offering, +2 more

6 terms

Schedule 13D/A regulatory

"This Amendment No. 13 (this "Amendment No. 13" or this "/A") amends and supplements the statement on originally filed..."

A Schedule 13D/A is an amended disclosure filed with regulators by an investor who already reported owning more than 5% of a company’s shares and needs to update their original filing. Think of it as a public status update that tells markets whether the investor’s ownership, plans, or source of funds have changed; such updates matter because they can signal a push for control, major strategic moves, or increased pressure on management, which can affect stock prices.

pre-funded warrants financial

"pre-funded warrants ("Pre-Funded Warrants") exercisable for up to 8,178,412 shares of common stock directly held by the Fund."

Pre-funded warrants are financial instruments that give investors the right to purchase a company's stock at a set price, but with most or all of the purchase price paid upfront. They function like a coupon or gift card for stock, allowing investors to buy shares later at a fixed price, which can be beneficial if they want to avoid future price increases. This makes them important for investors seeking flexibility and certainty in their investment plans.

Beneficial Ownership Blocker regulatory

"The Pre-Funded Warrants contain a provision (the "Beneficial Ownership Blocker"), which precludes the exercise..."

A beneficial ownership blocker is a legal or structural device that prevents a shareholder from being treated as the ultimate owner of enough shares to trigger control, reporting, or voting thresholds. Think of it like a speed bump that stops an investor from reaching a stake size that would force corporate disclosure or change control rights. Investors care because it affects who controls the company, how shares vote, regulatory filings, takeover risk and therefore potential value or liquidity of their holdings.

at-the-market offering financial

"On June 22, 2026, the Fund purchased 2,358,048 shares of common stock in an at-the-market offering by the Issuer (the "ATM Offering")..."

An at-the-market offering is a method companies use to sell new shares of stock directly into the open market over time, rather than all at once. This allows them to raise money gradually, similar to selling small pieces of a product instead of a large batch. For investors, it means the company can access funding more flexibly, but it may also increase the supply of shares and influence the stock’s price.

beneficial owner regulatory

"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..."

A beneficial owner is the person who ultimately owns or controls a financial asset or property, even if their name isn't directly on official documents. Think of it like someone who secretly holds the keys to a safe deposit box—others may appear to have access, but the true owner is the one who benefits from what's inside. Identifying beneficial owners helps ensure transparency and prevent illegal activities like money laundering or fraud.

investment adviser financial

"RA Capital serves as investment adviser for each of the Fund, the Nexus Fund and the Account..."

An investment adviser is a person or firm that professionally manages money and gives recommendations about buying, selling, or holding investments. Like a financial coach or guide, they have a legal duty to act in a client's best financial interest, so their advice, fees and potential conflicts can directly affect returns and risk — making their role important for investors who want informed, accountable help with portfolios.

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Available on EDGAR 06/24/2026 - 06:49 PM Accepted by SEC EDGAR 06/24/2026 - 06:49 PM Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 13)

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)

06/22/2026

(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).

schemaVersion:

SCHEDULE 13D

CUSIP Number(s): 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 12,036,126.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 12,036,126.00

11

Aggregate amount beneficially owned by each reporting person

12,036,126.00

12

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

13

Percent of class represented by amount in Row (11)

11.9 %

14

Type of Reporting Person (See Instructions)

IA, PN

SCHEDULE 13D

CUSIP Number(s): 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 12,036,126.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 12,036,126.00

11

Aggregate amount beneficially owned by each reporting person

12,036,126.00

12

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

13

Percent of class represented by amount in Row (11)

11.9 %

14

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13D

CUSIP Number(s): 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 12,036,126.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 12,036,126.00

11

Aggregate amount beneficially owned by each reporting person

12,036,126.00

12

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

13

Percent of class represented by amount in Row (11)

11.9 %

14

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13D

CUSIP Number(s): 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 11,897,896.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 11,897,896.00

11

Aggregate amount beneficially owned by each reporting person

11,897,896.00

12

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

13

Percent of class represented by amount in Row (11)

11.8 %

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. 13 (this "Amendment No. 13" 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, February 21, 2025, August 14, 2025, March 9, 2026 and March 17, 2026 (as amended, the "Statement") by the Reporting Persons. Unless otherwise defined herein, capitalized terms used in this Amendment No. 13 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) 11,897,896 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 8,178,412 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 by virtue of the Beneficial Ownership Blocker. 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 18, 2026, the Fund purchased 338,100 shares of common stock at prices ranging from $8.25 to $8.35 and a weighted-average price of $8.30 per share through open market purchases. On June 22, 2026, the Fund purchased 2,358,048 shares of common stock in an at-the-market offering by the Issuer (the "ATM Offering") at a price of $8.20 per share. All purchases of the securities described herein were for cash and were funded by working capital of the Fund.
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) 98,449,606 shares of common stock outstanding as of May 8, 2026, as reported in the Issuer's Quarterly Report on Form 10-Q filed with the SEC on May 12, 2026; and (ii) 2,358,048 shares of common stock issued to the Fund in the ATM Offering.
(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 since the most recent amendment to this Schedule 13D/A.
(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/A filed with the SEC on February 21, 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:	06/24/2026

Peter Kolchinsky

Signature:	/s/ Peter Kolchinsky
Name/Title:	Peter Kolchinsky
Date:	06/24/2026

Rajeev Shah

Signature:	/s/ Rajeev Shah
Name/Title:	Rajeev Shah
Date:	06/24/2026

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:	06/24/2026

FAQ

How much of Solid Biosciences (SLDB) does RA Capital now beneficially own?

RA Capital and related entities report beneficial ownership of 12,036,126 Solid Biosciences shares, representing 11.9% of the company’s common stock. This percentage is based on 98,449,606 shares outstanding as of May 8, 2026, plus 2,358,048 new shares issued in an ATM.

What new Solid Biosciences (SLDB) share purchases did RA Capital make in June 2026?

In June 2026, RA Capital Healthcare Fund bought 338,100 SLDB shares in open-market trades at prices from $8.25 to $8.35 and 2,358,048 shares at $8.20 each in an at-the-market offering by Solid Biosciences, paid from the Fund’s working capital.

What are the pre-funded warrants RA Capital holds in Solid Biosciences (SLDB)?

RA Capital Healthcare Fund holds pre-funded warrants exercisable for up to 8,178,412 SLDB shares. A Beneficial Ownership Blocker prevents exercising these warrants if doing so would push the Fund and its affiliates above 9.99% of Solid Biosciences’ outstanding common stock.

How is RA Capital’s 11.9% ownership in Solid Biosciences (SLDB) calculated?

The 11.9% figure uses 98,449,606 SLDB shares outstanding as of May 8, 2026, reported in Solid’s Form 10-Q, plus 2,358,048 shares issued to RA Capital’s Fund in an at-the-market offering on June 22, 2026.

Who are the reporting persons in the Solid Biosciences (SLDB) Schedule 13D/A?

The Schedule 13D/A is filed on behalf of RA Capital Management, L.P., RA Capital Healthcare Fund, L.P., Peter Kolchinsky, and Rajeev Shah. RA Capital serves as investment adviser to the funds and account holding SLDB securities, with Kolchinsky and Shah managing RA Capital.

Does RA Capital fully control the Solid Biosciences (SLDB) shares held by its funds?

RA Capital has been delegated sole voting and dispositive power over SLDB shares held by RA Capital Healthcare Fund and RA Capital Nexus Fund. The funds disclaim beneficial ownership because they have divested voting and investment power and cannot revoke this delegation on less than 61 days’ notice.