These disorders, which are caused by mutations in the genes that directly or indirectly interact with FGF23, include hyperphosphatemic familial tumoral calcinosis, hereditary hypophosphatemic rickets with hypercalciuria, autosomal recessive hypophosphatemic rickets, and X-linked dominant hypophosphatemic rickets. The gene discussed is FGF23; the disease is familial tumoral calcinosis.