The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

  NAMES OF REPORTING PERSONS

  Third Rock Ventures IV, L.P.

  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

  (a)  ☐        (b)  ☑

  SEC USE ONLY

  CITIZENSHIP OR PLACE OF ORGANIZATION

  Delaware

NUMBER OF

SHARES

 BENEFICIALLY 

OWNED BY

EACH

REPORTING

PERSON

WITH

  SOLE VOTING POWER

  0

  SHARED VOTING POWER

  2,343,154

  SOLE DISPOSITIVE POWER

  0

  SHARED DISPOSITIVE POWER

  2,343,154

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  2,343,154

  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

  10.0% (1)

  TYPE OF REPORTING PERSON

  PN

The percent of class was calculated based on 23,340,544 shares of common stock issued and outstanding as of November 8, 2019, as disclosed in the Issuer’s 10-Q filed with the Securities and Exchange Commission on November 14, 2019.

  NAMES OF REPORTING PERSONS

  Third Rock Ventures GP IV, L.P.

  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

  (a)  ☐        (b)  ☑

  SEC USE ONLY

  CITIZENSHIP OR PLACE OF ORGANIZATION

  Delaware

NUMBER OF

SHARES

 BENEFICIALLY 

OWNED BY

EACH

REPORTING

PERSON

WITH

  SOLE VOTING POWER

  0

  SHARED VOTING POWER

  2,343,154

  SOLE DISPOSITIVE POWER

  0

  SHARED DISPOSITIVE POWER

  2,343,154

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  2,343,154

  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

  10.0% (1)

  TYPE OF REPORTING PERSON

  PN

The percent of class was calculated based on 23,340,544 shares of common stock issued and outstanding as of November 8, 2019, as disclosed in the Issuer’s 10-Q filed with the Securities and Exchange Commission on November 14, 2019.

  NAMES OF REPORTING PERSONS

  TRV GP IV, LLC

  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

  (a)  ☐        (b)  ☑

  SEC USE ONLY

  CITIZENSHIP OR PLACE OF ORGANIZATION

  Delaware

NUMBER OF

SHARES

 BENEFICIALLY 

OWNED BY

EACH

REPORTING

PERSON

WITH

  SOLE VOTING POWER

  0

  SHARED VOTING POWER

  2,343,154

  SOLE DISPOSITIVE POWER

  0

  SHARED DISPOSITIVE POWER

  2,343,154

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  2,343,154

  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES   ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

  10.0% (1)

  TYPE OF REPORTING PERSON

  OO

The percent of class was calculated based on 23,340,544 shares of common stock issued and outstanding as of November 8, 2019, as disclosed in the Issuer’s 10-Q filed with the Securities and Exchange Commission on November 14, 2019.

Item 1.

Issuer

(a)

Name of Issuer:

Fulcrum Therapeutics, Inc. (the “Issuer”)

(b)

Address of Issuer’s Principal Executive Offices:

26 Landsdowne Street

Cambridge, MA 02139

Item 2.

Filing Person

(a) – (c)

Name of Persons Filing; Address; Citizenship:

(i) Third Rock Ventures IV, L.P. (“TRV IV”);

(ii)  Third Rock Ventures GP IV, L.P. (“TRV GP IV”), which is the sole general partner of TRV IV; and

(iii)  TRV GP IV, LLC (“TRV GP IV LLC,” and collectively with TRV IV and TRV GP IV, the “Reporting Persons”), which is the sole general partner of TRV GP IV.

The address of the principal business office of each of the Reporting Persons is Third Rock Ventures, LLC, 29 Newbury Street, 3rd Floor, Boston, MA 02116.

Each of TRV IV and TRV GP IV is a Delaware limited partnership. TRV GP IV LLC is a Delaware limited liability company.

(d)

Title of Class of Securities:

Common stock, $0.001 par value per share, (the “Common Stock”)

(e)

CUSIP Number:

359616109

Item 3.

If this statement is filed pursuant to Rules 13d-1(b), or 13d-2(b) or (c), check whether the person filing is a:

(a)

☐

Broker or dealer registered under Section 15 of the Act;

(b)

☐

Bank as defined in Section 3(a)(6) of the Act;

(c)

☐

Insurance company as defined in Section 3(a)(19) of the Act;

(d)

☐

Investment company registered under Section 8 of the Investment Company Act of 1940;

(e)

☐

An investment adviser in accordance with Rule 13d-1(b)(1)(ii)(E);

(f)

☐

An employee benefit plan or endowment fund in accordance with Rule 13d-1(b)(1)(ii)(F);

(g)

☐

A parent holding company or control person in accordance with Rule 13d-1(b)(1)(ii)(G);

(h)

☐

A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i)

☐

(j)

☐

A non-U.S. institution in accordance with Rule 240.13d-1(b)(1)(ii)(J);

(k)

☐

Item 4.

(a) and (b)

Amount beneficially owned:

(i) TRV IV directly owns 2,343,154 shares of Common Stock (the “Shares”), which represents approximately 10.0% of the outstanding shares of Common Stock.

(ii)  TRV GP IV is the general partner of TRV IV and may be deemed to beneficially own the Shares.

(iii)  TRV GP IV LLC is the general partner of TRV GP IV and may be deemed to beneficially own the Shares.

Reporting Person

(i) Sole power to vote or direct the vote

(ii)  Shared power to vote or to direct the vote

(iii)  Sole power to dispose or to direct the disposition of

(iv) Shared power to dispose or to direct the disposition of

Item 5.

Ownership of Five Percent or Less of a Class.

Not applicable.

Item 6.

Ownership of More than Five Percent on Behalf of Another Person.

Not applicable.

Item 7.

Not applicable.

Item 8.

Identification and Classification of Members of the Group.

Not applicable.

Item 9.

Notice of Dissolution of Group.

Not applicable.

Item 10.

Certification.

Not applicable.