FGF23 and familial hyperphosphatemic tumoral calcinosis/hyperphosphatemic hyperostosis syndrome: Hyperphosphatemic familial tumoral calcinosis (HFTC) is a rare autosomal recessive disorder characterized by ectopic calcifications in periarticular soft tissues due to mutations in genes such as GALNT3, FGF23, or KL, leading to FGF23 deficiency or resistance and subsequent hyperphosphatemia.