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

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

SCHEDULE 13D

(Rule 13d-101)

Information to be Included in Statements Filed Pursuant

to § 240.13d-1(a) and Amendments Thereto Filed

Pursuant to § 240.13d-2(a)

Under the Securities Exchange Act of 1934

(Amendment No.    )

Dicerna
Pharmaceuticals, Inc.

(Name of Issuer)

Common Stock, $0.0001

par value per share

(Title of Class of Securities)

253031108

(CUSIP Number)

Bain Capital Life Sciences Investors, LLC

200 Clarendon Street

Boston, MA 02116

617-516-2000

(Name,
Address and Telephone Number of Person Authorized to Receive Notices and Communications)

April 11, 2017

(Date of Event Which Requires Filing of This Statement)

If the filing person has
previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following
box.  ☐

Note. Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See§ 240.13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this
cover page shall not be deemed to be filed for the purpose of Section 18 of the Securities Exchange Act of 1934, as amended (Act), or otherwise subject to the liabilities of that section of the Act but shall be subject to all
other provisions of the Act (however, see the Notes).