Ultragenyx Pharmaceutical Inc. and partner Kyowa Hakko Kirin Co. Ltd. (KHK) have won FDA approval for Crysvita (burosumab), making it the first U.S.-approved treatment for X-linked hypophosphatemia (XLH), a rare, inherited form of rickets. The chronic progressive musculoskeletal disorder is estimated to affect about 3,000 children and 9,000 adults in the U.S.