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). The gene discussed is FGF23; the disease is hyperphosphatemia.