13D Filing: RA Capital Management and Dicerna Pharmaceuticals Inc (DRNA)

Explanatory Note

This Amendment No. 4 to
Schedule 13D (this “Amendment No. 4”) amends and supplements the Statement on Schedule 13D filed with the United
States Securities and Exchange Commission on February 5, 2014, as amended to date (the “Statement”) by (i) RA
Capital Management, LLC (the “RA Capital”), (ii) Peter Kolchinsky and (iii) RA Capital Healthcare Fund, L.P.
(“Fund” and together with each of the foregoing, the “Reporting Persons”), relating to the Common
Stock (the “Common Stock”) of Dicerna Pharmaceuticals, Inc. (the “Issuer”). Capitalized terms
used herein without definition shall have the meaning set forth in the Statement.

Item 5(a)-(b) of the Statement is hereby amended
and restated in its entirety as follows:

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

Item 5(c) of the Statement is hereby amended
and supplemented by adding the following:

(c) From the date of the most recent amendment
to this Schedule 13D through January 18, 2018, the Reporting Persons disposed of 611,700 shares of Common Stock in a series of
open market transactions on the Nasdaq Global Market. Details by date of the transactions are as follows:

(d) None.

(e) Not Applicable.