UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

(Amendment No.     )*

Solid Biosciences Inc.

(Name of Issuer)

Common Stock, par value $0.001 per share

(Title of Class of Securities)

83422E105

(CUSIP Number)

May 9, 2018

(Date of Event which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

☐ Rule 13d-1(b)

☒ Rule 13d-1(c)

☐ Rule 13d-1(d)

The information required in 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).

CUSIP No. 83422E105

CUSIP No. 83422E105

CUSIP No. 83422E105

CUSIP No. 83422E105

Item 1(a). Name of Issuer:

Solid Biosciences Inc. (the “Issuer”)

Item 1(b). Address of Issuer’s Principal Executive Offices:

141 Portland Street, Fifth Floor

Cambridge, MA 02139

Item 2(a). Name of Person Filing:

This Schedule 13G is jointly filed by Boxer Capital, LLC (“Boxer Capital”), Boxer Asset Management Inc. (“Boxer Management”), Joe Lewis and MVA Investors, LLC (“MVA Investors”) (together with Boxer Capital, Boxer Management and Joe Lewis, the “Reporting Persons”). Boxer Management is the managing member and majority owner of Boxer Capital. Joe Lewis is the sole indirect beneficial owner of and controls Boxer Management. MVA Investors is the independent, personal investment vehicle of certain employees of Boxer Capital, and is controlled by employees of Boxer Capital that are members of MVA Investors. As such, MVA Investors is not controlled by any of the other Reporting Persons.

Item 2(b). Address of Principal Business Office, or, if none, Residence:

The principal business address of Boxer Capital and MVA Investors is: 11682 El Camino Real, Suite 320, San Diego, CA 92130. The principal business address of Boxer Management and Joe Lewis is: Cay House, EP Taylor Drive N7776, Lyford Cay, New Providence, Bahamas.

Item 2(c). Citizenship:

Boxer Capital is a limited liability company organized under the laws of Delaware. Boxer Management is a corporation organized under the laws of the Bahamas. Joe Lewis is a citizen of the United Kingdom. MVA Investors is a limited liability company organized under the laws of Delaware.

Item 2(d). Title of Class of Securities:

Common Stock, par value $0.001 per share (the “Common Stock”).

Item 2(e). CUSIP Number:

83422E105

Item 3. If this statement is filed pursuant to Rule 13d-1(b), or 13d-2(b) or (c), check whether the person filing is a:

Not applicable.

Item 4. Ownership.

Boxer Capital, Boxer Management and Joe Lewis beneficially own 2,200,000 shares of Common Stock. MVA Investors beneficially owns 40,280 shares of Common Stock. The Reporting Persons may be deemed to beneficially own 2,240,280 shares of Common Stock in the aggregate.

The shares of Common Stock beneficially owned by Boxer Capital, Boxer Management and Joe Lewis represent 6.2%* of the Issuer’s outstanding shares of Common Stock. The shares of Common Stock beneficially owned by MVA Investors represent 0.1%* of the Issuer’s outstanding shares of Common Stock. The shares of Common Stock owned by the Reporting Persons in the aggregate represent 6.3%* of the Issuer’s outstanding shares of Common Stock.

MVA Investors has sole power to vote or to direct the vote of the 40,280 shares of Common Stock it beneficially owns.

Boxer Capital, Boxer Management and Joe Lewis have shared power to vote or to direct the vote of the 2,200,000 shares of Common Stock they beneficially own.

MVA Investors has sole power to dispose or to direct the disposition of the 40,280 shares of Common Stock it beneficially owns.

Boxer Capital, Boxer Management and Joe Lewis have shared power to dispose or to direct the disposition of the 2,200,000 shares of Common Stock they beneficially own.

Not applicable.

Only Boxer Capital has the right to receive dividends and the proceeds from the sale of the shares of Common Stock held by Boxer Capital. Only MVA Investors has the right to receive dividends and the proceeds from sale of the shares of common stock held by MVA Investors.

Not applicable.

Not applicable.

Not applicable.

Item 10. Certification.

(c) By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.

Exhibits

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.

May 18, 2018

Exhibit 1

JOINT FILING AGREEMENT

The undersigned hereby agree that the Statement on Schedule 13G with respect to the shares of Solid Biosciences Inc., common stock, par value $0.001 per share, is, and any amendments thereto executed by each of us shall be, filed on behalf of each of us pursuant to and in accordance with the provisions of Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, as amended, and that this Agreement shall be included as an Exhibit to the Schedule 13G and each such amendment. Each of the undersigned agrees to be responsible for the timely filing of the Schedule 13G and any amendments thereto, and for the completeness and accuracy of the information concerning itself contained therein. This Agreement may be executed in any number of counterparts, all of which taken together shall constitute one and the same instrument.

IN WITNESS WHEREOF, the undersigned have executed this Agreement as of May 18, 2018.