FGF23 and rickets: As a result of the complications related to phosphate metabolism in FD/MAS, there has been great interest in new medications that can target the excess FGF23 production seen in FD.33, –35 Burosumab is a monoclonal antibody targeting FGF23 and is FDA approved for X-linked hypophosphatemic rickets and tumor-induced osteomalacia.36,37 FD lesions produce FGF23,33 which can cause hypophosphatemia and subsequent hypophosphatemic bone pain and rickets.