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

(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.