FGF23 and X-linked hypophosphatemia: <h4>Background</h4>Fibroblast growth factor 23 (FGF23)-related hypophosphatemic rickets/osteomalacia arises from excessive FGF23 activity, with X-linked hypophosphatemia (XLH) and tumor-induced osteomalacia (TIO) as the most common congenital and acquired forms, respectively.