Among them are the phosphate-regulating gene homologous to endopeptidase on X chromosome (PHEX), dentin matrix protein 1 (DMP1), and family with sequence similarity 20, member C (FAM20C). Inactivating mutations in these genes cause hypophosphatemia and impaired skeletal mineralization by increasing the production of FGF23 in osteocytes (8). The gene discussed is DMP1; the disease is hypophosphatemia.