Amendment No. 1 to Schedule 13D for Jade Biosciences, Inc.

This Amendment No. 1 to Schedule 13D, filed by Fairmount Funds Management LLC and related entities, updates the ownership and transaction details regarding the Common Stock of Jade Biosciences, Inc. The amendment highlights that the Reporting Persons now have voting and dispositive power over 10,353,875 shares of Common Stock, which includes shares held directly, shares issuable upon the exercise of Pre-Funded Warrants, and shares issuable upon conversion of Series A Preferred Stock. The amendment also details a private placement transaction on October 6, 2025, where Fund II purchased 1,333,126 shares of Common Stock and Pre-Funded Warrants to purchase 855,047 shares for an aggregate purchase price of $19,999,815.72. The filing includes updates to the Subscription Agreement, Pre-Funded Warrants, and Registration Rights Agreement, which govern the terms of the private placement and the registration of the resale of the shares.