Hyperphosphatemic Familial Tumoral Calcinosis (HFTC) and Hyperphosphatemic Hyperostosis Syndrome (HHS) are associated with autosomal recessive mutations in three different genes, FGF23, GALNT3 and KL, leading to reduced levels of fibroblast growth factor 23 (FGF23) and subsequent clinical effects. This evidence concerns the gene GALNT3 and familial hyperphosphatemic tumoral calcinosis/hyperphosphatemic hyperostosis syndrome.