13D Filing: RA Capital Management and Solid Biosciences Inc (SLDB)

SCHEDULE 13D

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)

RA Capital Management, LLC

20 Park Plaza, Suite 1200

Boston, MA 02116

Telephone: 617.778.2512

Attn: Peter Kolchinsky

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

January 30, 2018

(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. [ ]

Note: Schedules filed in paper format shall include a
signed original and five copies of the schedule, including all exhibits. See Rule 13d-7 for other parties to whom copies are to
be sent.

* The remainder of this cover page shall be filled out for a
reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment
containing information which would alter disclosures provided in a prior cover page.

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).

¹ The reporting person is the beneficial
owner of 2,689,444 shares of the Issuer’s Common Stock which constitute approximately 7.87% of the class outstanding. The
percentage calculation assumes that there are currently 34,151,022 outstanding shares of Common Stock of the Issuer, based upon
the closing of the Issuer’s initial public offering, as reported in the Issuer’s prospectus filed with the Securities
and Exchange Commission (“SEC”) on January 29, 2018.

² The reporting person is the beneficial
owner of 2,689,444 shares of the Issuer’s Common Stock which constitute approximately 7.87% of the class outstanding. The
percentage calculation assumes that there are currently 34,151,022 outstanding shares of Common Stock of the Issuer, based upon
the closing of the Issuer’s initial public offering, as reported in the Issuer’s prospectus filed with the SEC on
January 29, 2018.

SCHEDULE 13D

This Schedule 13D relates to common
stock, par value $0.001 per share (the “Common Stock”), of Solid Biosciences Inc., a Delaware corporation (the “Issuer”).  The
address of the principal executive offices of the Issuer is: 161 First Street, Third Floor, Cambridge, MA 02142.

(a) This Schedule 13D is being
filed on behalf of (i) RA Capital Management, LLC (“RA Capital”) and (ii) Peter Kolchinsky and together with
each of the foregoing, the “Reporting Persons”).

Common Stock reported herein for RA Capital
represent shares reported for RA Capital Healthcare Fund, L.P. (the “Fund”) as well as shares held in a separately
managed account (the “Account”). RA Capital is the general partner of the Fund and serves as investment adviser for
the Account. Peter Kolchinsky is the manager of RA Capital. As the investment adviser to the Fund and the Account, RA Capital may
be deemed a beneficial owner, for purposes of Section 13(d) of the Securities Exchange Act of 1934 (the “Act”), of
any securities of the Issuer owned by the Fund or the Account. As the manager of RA Capital, Mr. Kolchinsky may be deemed a beneficial
owner, for purposes of Section 13(d) of the Act, of any securities of the Issuer beneficially owned by RA Capital. RA Capital is
a registered investment adviser within the meaning of Rule 13d-1(b)(1)(ii)(E) and Rule 16a-1(a)(v), and Mr. Kolchinsky is a parent
or control person of RA Capital within the meaning of Rule 13d-1(b)(1)(ii)(G) and Rule 16a-1(a)(1)(vii). RA Capital and Mr. Kolchinsky
disclaim beneficial ownership of the securities reported in this Schedule 13D Statement (the “Statement”) other than
for the purpose of determining their obligations under Section 13(d) of the Act, and neither the filing of the Statement nor the
filing of this Amendment shall be deemed an admission that either RA Capital or Mr. Kolchinsky is the beneficial owner of such
securities for any other purpose.

(b) The business address of each of
the Reporting Persons is: 20 Park Plaza, Suite 1200, Boston, MA 02116.

(c) The Fund is a private investment
vehicle. RA Capital provides investment management services to the Fund and the Account. The principal occupation of Mr. Kolchinsky
is investment management.

(d) None of the Reporting Persons
has, during the last five years, been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).

(e) None of the Reporting Persons
has, during the last five years, 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 or 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.

Prior to the Issuer’s initial public
offering (the “IPO”), the Reporting Persons acquired equity interests in the Issuer’s
predecessor in a private placement, and those interests converted into 1,689,444 shares of Common Stock prior to consummation of
the IPO. The Reporting Persons purchased 1,000,000 shares of Common Stock from the underwriters of the IPO. All purchases were
for cash and were funded by working capital of the Fund and the Account.

The Reporting Persons acquired the Common
Stock reported herein for investment purposes and not with an intent, purpose or effect of changing control of the Issuer. Although
the Reporting Persons currently have no plan or proposal to acquire any additional Common Stock or to dispose of any of the Common
Stock reported herein, the Reporting Persons may acquire additional Common Stock from time to time or dispose of Common Stock they
beneficially own, consistent with their investment purposes and in amounts to be determined by the Reporting Persons based upon
a number of factors, including, without limitation, their ongoing assessment of the Issuer’s business prospects, prevailing market
conditions, the availability of other investment opportunities, and/or other considerations.

In addition, consistent with their investment
purpose, the Reporting Persons may engage in communications with persons associated with the Issuer, including shareholders of
the Issuer, officers of the Issuer and/or members of the board of directors of the Issuer, to discuss matters regarding the Issuer,
including but not limited to its operations and strategic direction. Mr. Rajeev Shah, a portfolio manager and managing director
of RA Capital, currently serves as a director of the Issuer and therefore will engage in regular discussions with the Issuer’s
board of directors and management as part of his duties as a director.

The Reporting Persons have no plans or
proposals that relate to, or could result in, any of the matters referred to in paragraphs (a) through (j), inclusive, of the instructions
to Item 4 of Schedule 13D.

The Reporting Persons may, however, change
their purpose and formulate and implement plans or proposals with respect to the Issuer at any time and from time to time. Any
such action may be made by the Reporting Persons alone or in conjunction with other shareholders, potential acquirers, financing
sources and/or other third parties and could include one or more purposes, plans or proposals that relate to or would result in
actions required to be reported herein in accordance with Item 4 of Schedule 13D.

(a) and (b) See Items 7-11 of the cover
pages and Item 2 above.

(c) The following table lists the Reporting
Persons’ transactions in Common Stock that were effected during the sixty day period prior to the filing of this Schedule
13D:

(1) The Reporting Persons acquired Series
1 Senior Preferred Units, Series C Common Units, and Series 2 Senior Preferred Units of the Issuer’s predecessor more than
60 days prior to the IPO. All units converted automatically on a 1-for-.8485 basis into Common Stock prior to the IPO.

Shares marked with an * were acquired by
the Fund. The remaining shares were acquired for the Account.

(d) Not applicable.

(e) Not applicable.

The Reporting Persons have entered into
a standard lock-up agreement with the Issuer and the underwriters of the IPO, prohibiting any sale of the Common Stock reported
herein during the 180 days following the closing of the offering. The Reporting Persons may be released from lock-up prior to the
expiration of the lock-up period at the sole discretion of the underwriters.

Exhibit 1 Joint Filing Agreement by
and among the Reporting Persons.

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.

Date: February 9, 2018

RA CAPITAL MANAGEMENT, LLC

By: /s/ Peter Kolchinsky

————————————————-

Peter Kolchinsky

Manager

PETER KOLCHINSKY

/s/ Peter Kolchinsky

————————————————-

Exhibit 1

JOINT FILING AGREEMENT

This Joint Filing Agreement,
dated as of February 9, 2018, is by and among RA Capital Management, LLC and Peter
Kolchinsky (the foregoing are collectively referred to herein as the “Filers”).

Each of the Filers
may be required to file with the United States Securities and Exchange Commission a statement on Schedule 13G and/or 13D with respect
to Common Stock of Solid Biosciences Inc. beneficially owned by them from time to time.

Pursuant to and in
accordance with Rule 13(d)(1)(k) promulgated under the Securities Exchange Act of 1934, as amended, the Filers hereby agree to
file a single statement on Schedule 13G and/or 13D (and any amendments thereto) on behalf of each of such parties, and hereby further
agree to file this Joint Filing Agreement as an exhibit to such statement, as required by such rule.

This Joint Filing Agreement
may be terminated by any of the Filers upon one week’s prior written notice or such lesser period of notice as the Filers
may mutually agree.

Executed and delivered
as of the date first above written.

RA CAPITAL MANAGEMENT, LLC

By: /s/ Peter Kolchinsky

————————————————-

Peter Kolchinsky

Manager

PETER KOLCHINSKY

/s/ Peter Kolchinsky

————————————————-