X0306 4 2019-07-22 0 0001680581 Fulcrum Therapeutics, Inc. FULC 0001569705 Third Rock Ventures III, L.P. C/O THIRD ROCK VENTURES, LLC, 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 0001637300 Third Rock Ventures GP III, L.P. 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 0001637299 TRV GP III, LLC 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 0001192603 STARR KEVIN P 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 0001192595 TEPPER ROBERT I 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 Common Stock 2019-07-22 4 C 0 5595238 A 5880952 D Common Stock 2019-07-22 4 P 0 81250 16.00 A 5962202 D Series A Preferred Stock 2019-07-22 4 C 0 39166667 0.00 D Common Stock 5595238 0 D Series A Preferred Stock 2019-07-22 4 C 0 0 0.00 D Common Stock 0 0 D The shares are directly held by Third Rock Ventures III, L.P. ("TRV III"). The general partner of TRV III is Third Rock Ventures GP III, L.P. ("TRV GP III LP"). The general partner of TRV GP III LP is TRV GP III, LLC ("TRV GP III LLC"). The individual managers of TRV GP III LLC are Mark Levin ("Levin"), Kevin Starr ("Starr") and Dr. Robert Tepper ("Tepper"). Each of TRV GP III LP, TRV GP III LLC, Levin, Starr and Tepper disclaims beneficial ownership of the shares except to the extent of its or his pecuniary interest therein, if any, and this report shall not be deemed an admission that it or he is the beneficial owner of such shares. As of the date of this filing, Third Rock Ventures IV, L.P. ("TRV IV") holds 2,261,904 shares of Common Stock issued upon conversion of 15,833,333 shares of Series A Preferred Stock. The general partner of TRV IV is Third Rock Ventures GP IV, L.P. ("TRV GP IV"). The general partner of TRV GP IV is TRV GP IV, LLC ("TRV GP IV LLC"). Abbie Celniker, Ph.D., Tepper, Alexis Borisy, Craig Muir and Cary Pfeffer, M.D. are the managing members of TRV IV LLC who collectively make voting and investment decisions with respect to shares held by TRV IV LP. Tepper disclaims beneficial ownership of the shares except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares. On July 22, 2019, the Series A Preferred Stock converted into Common Stock on a seven-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series A Preferred Stock was convertible at any time at the holder's election and automatically upon the closing of the Issuer's initial pubic offering. The shares had no expiration date. /s/ Kevin Gillis, Chief Financial Officer of TRV GP III, LLC, general partner of Third Rock Ventures GP III, L.P., general partner of Third Rock Ventures III, L.P. 2019-07-22 /s/ Kevin Gillis, Chief Financial Officer of TRV GP III, LLC, general partner of Third Rock Ventures GP III, L.P. 2019-07-22 /s/ Kevin Gillis, Chief Financial Officer of TRV GP III, LLC 2019-07-22 /s/ Kevin Gillis by power of attorney for Kevin Starr 2019-07-22 /s/ Kevin Gillis by power of attorney for Dr. Robert Tepper 2019-07-22