FGF23 and calcification: Inactivating mutations in FGF23, KLOTHO, and GALNT3 encoding GalNAc-T3, an enzyme required for O-glycosylation of FGF23, are responsible for hyperphosphatemic familial tumoral calcinosis (HFTC) associated with hyperphosphatemia, normal to elevated serum 1,25(OH)2D levels, and massive ectopic calcification (34, 45, 46).