Familial tumoral calcinosis (FTC)/hyperostosis-hyperphosphatemia syndrome (HHS) is a rare disorder caused by mutations in the genes encoding fibroblast growth factor-23 (FGF23), N-acetylgalactosaminyltransferase 3 (GALNT3), or KLOTHO.
To date, recessive mutations have been described in three genes involving phosphate metabolism: FGF23, GALNT3, and α-Klotho, all of which result in the phenotypic presentation of hFTC.