13G Filing: James E. Flynn and Mirna Therapeutics Inc. (MIRN)

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Exhibit A

Agreement

The undersigned agree that this
Schedule 13G, and all amendments thereto, relating to the Common Stock of Synlogic, Inc. shall be filed on behalf of the
undersigned.

DEERFIELD MANAGEMENT COMPANY, L.P.

By: Flynn Management LLC, General Partner

By: /s/ Jonathan Isler

       Jonathan Isler, Attorney-In-Fact

DEERFIELD MGMT III, L.P.

By: J.E. Flynn Capital III, LLC, General Partner

By: /s/ Jonathan Isler

       Jonathan Isler, Attorney-In-Fact

DEERFIELD PRIVATE DESIGN FUND III, L.P.

By: Deerfield Mgmt III, L.P., General Partner

By: J.E. Flynn Capital III, LLC, General Partner

By: /s/ Jonathan Isler

       Jonathan Isler, Attorney-In-Fact

JAMES E. FLYNN


/s/ Jonathan Isler 

Jonathan Isler, Attorney-In-Fact

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