Definition:

Familial tumoral calcinosis (FTC) refers to a group of disorders inherited in an autosomal recessive fashion, distinguished by the development of ectopic and vascular calcified masses that occur in settings of hyperphosphatemia (hFTC) and normophosphatemia (nFTC). hFTC is characterized by increased re-absorption of phosphate through the renal proximal tubule, resulting in elevated phosphate concentration and deposition of calcified deposits in cutaneous and subcutaneous tissues, occasionally, in visceral organs. hFTC has been shown to result from mutations in three genes: fibroblast growth factor-23 (FGF23), KL encoding Klotho, and GALNT3, which encodes a glycosyltransferase responsible for FGF23 O-glycosylation; defective function of any one of these three proteins results in hyperphosphatemia and ectopic calcification. nFTC is characterized by absence of metabolic abnormalities. nFTC has been found to be associated with absence of functional SAMD9, a putative tumor suppressor and anti-inflammatory protein.