On December 24, 2019, Mirum Pharmaceuticals, Inc. entered into a letter agreement with Michael Grey that amends that certain Amended and Restated Offer Letter by and between the Company and Michael Grey, dated May 15, 2019. Pursuant to the Letter Agreement and effective January 1, 2020, as part of a planned management transition, Mr. Grey resigned from his role as an executive officer of the company in his capacity as Executive Chairman. Mr. Grey will remain a member of the Company's board of directors and will serve as a non-employee director and Chairman of the Board.