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

Explanatory Note

This Amendment No. 3 to
Schedule 13D (this “Amendment No. 3”) 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 4. Purpose of Transaction

Item 4 of the Statement is hereby amended
and supplemented by adding the following:

On December 18, 2017,
pursuant to the Letter Agreement, all the outstanding shares of Redeemable Convertible Preferred Stock held by the Reporting Persons
were converted into Common Stock (the “Conversion”). In consideration for their agreement to the Conversion,
the waiver of their right to participate as selling stockholders in the public offering and the amendment to the Registration Rights
Agreement, in connection with the Conversion, pursuant to the Letter Agreement, the Reporting Persons also received the Additional
Shares. The total number of shares of Common Stock received by the Fund and the Account pursuant to the Letter Agreement is 2,158,681
shares and 486,761 shares, respectively. Following such transactions, no shares of Redeemable Convertible Preferred Stock remain
outstanding.

Item 5. Interest in Securities of the Issuer

Item 5 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.

(c) Except for the transactions disclosed
in Item 4 herein, none of the Reporting Persons has effected any transactions in the Common Stock of the Issuer in the past 60
days.

(d) None.

(e) Not Applicable.