X0609 4 2026-09-09 false 0001755237 Korsana Biosciences, Inc. KRSA 0001802528 Fairmount Funds Management LLC false 200 BARR HARBOR DRIVE, SUITE 400 WEST CONSHOHOCKEN PA 19428 true false true false 0001769651 Fairmount Healthcare Fund II L.P. false 200 BARR HARBOR DRIVE, SUITE 400 WEST CONSHOHOCKEN PA 19428 true false true false 0002124208 Fairmount Healthcare Co-Invest VI L.P. false 200 BARR HARBOR DRIVE, SUITE 400 WEST CONSHOHOCKEN PA 19428 true false true false 0001830177 Kiselak Tomas false 200 BARR HARBOR DRIVE, SUITE 400 WEST CONSHOHOCKEN PA 19428 true false true false 0001663607 Harwin Peter Evan false 200 BARR HARBOR DRIVE, SUITE 400 WEST CONSHOHOCKEN PA 19428 true false true false false Stock Option (Right to Buy) 26.20 2026-09-09 4 A false 48445 0 A 2036-09-09 Common Stock 48445 48445 I By: Tomas Kiselak This option represents a right to purchase 48,445 shares of the Issuer's common stock. This option will vest in equal monthly installments through September 9, 2029, subject to the Reporting Person's continued service to the Issuer on each such vesting date. Fairmount Funds Management LLC ("Fairmount") is the investment manager for Fairmount Healthcare Fund II L.P. ("Fund II") and Fairmount Healthcare Co-Invest VI L.P. ("Co-Invest"). Peter Harwin and Tomas Kiselak are the managers of Fairmount. Under Mr. Kiselak's arrangement with Fairmount, Mr. Kiselak holds the option for one or more investment vehicles managed by Fairmount (each, a "Fairmount Fund"). Mr. Kiselak is obligated to turn over to Fairmount any net cash or stock received from the option for the benefit of such Fairmount Fund. Fairmount, Mr. Harwin, and Mr. Kiselak disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein. Fairmount, Fund II and Co-Invest may each be deemed a director by deputization of the Issuer by virtue of the fact that Tomas Kiselak serves on the board of directors of the Issuer and is a manager of Fairmount. /s/ Peter Harwin, Managing Member of Fairmount Funds Management LLC 2026-09-10 /s/ Peter Harwin, Managing Member of Fairmount Healthcare Fund II L.P. 2026-09-10 /s/ Peter Harwin, Managing Member of Fairmount Healthcare Co-Invest VI L.P. 2026-09-10 /s/ Tomas Kiselak 2026-09-10 /s/ Peter Harwin 2026-09-10