13D Filing: Bain Capital Life Sciences Fund, L.p. and Dicerna Pharmaceuticals Inc (NASDAQ:DRNA)

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CUSIP No. 253031108 13D Page
12

of 12

AGREEMENT REGARDING THE JOINT FILING OF

SCHEDULE 13D

The undersigned being duly
authorized thereunto, hereby execute this agreement as an exhibit to this Schedule 13D to evidence the agreement of the below-named parties, in accordance with the rules promulgated pursuant to the Securities Exchange Act of 1934, as amended, to
file this Schedule (including amendments thereto) jointly on behalf of each such party.

Dated: April 13, 2017

Bain Capital Life Sciences Fund, L.P.
By: Bain Capital Life Sciences Partners, LP, its general partner
By: Bain Capital Life Sciences Investors, LLC, its general partner
By:

/s/ Adam Koppel

Name: Adam Koppel
Title: Managing Director
BCIP Life Sciences Associates, LP
By: Boylston Coinvestors, LLC, its general partner
By:

/s/ Adam Koppel

Name: Adam Koppel
Title: Authorized Signatory

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