FGF23 and X-linked hypophosphatemia: The ADHR gene is a polypeptide that causes a phosphate-wasting disorder and is identified as fibroblast growth factor (FGF-23).13–15 FGF-23 has all of the predicted biological properties of phosphatonins.13, 14 High levels of FGF-23 have been demonstrated in tumors from patients with oncogenic osteomalacia and X-linked hypophosphatemia.