X0306 4 2019-07-22 0 0001680581 Fulcrum Therapeutics, Inc. FULC 0001688327 Third Rock Ventures IV, L.P. C/O THIRD ROCK VENTURES, LLC, 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 0001688326 Third Rock Ventures GP IV, L.P. 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 0001688325 TRV GP IV, LLC 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 Common Stock 2019-07-22 4 C 0 2261904 A 2261904 D Common Stock 2019-07-22 4 P 0 81250 16.00 A 2343154 D Series A Preferred Stock 2019-07-22 4 C 0 15833333 0.00 D Common Stock 2261904 0 D 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. These shares are directly held by Third Rock Ventures IV, L.P. ("TRV IV"). 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"). Each of TRV GP IV and TRV GP IV LLC disclaims beneficial ownership of these shares except to the extent of its pecuniary interest therein, if any, and this report shall not be deemed an admission that it is the beneficial owner of such shares. /s/ Kevin Gillis, Chief Financial Officer of TRV GP IV, LLC, general partner of Third Rock Ventures GP IV, L.P., general partner of Third Rock Ventures IV, L.P. 2019-07-22 /s/ Kevin Gillis, Chief Financial Officer of TRV GP IV, LLC, general partner of Third Rock Ventures GP IV, L.P. 2019-07-22 /s/ Kevin Gillis, Chief Financial Officer of TRV GP IV, LLC 2019-07-22