Elevated levels of FGF23 were reported mainly in genetic X-linked hypophosphatemia (XLH) and non-genetic tumor-induced osteomalacia (TIO), a rare condition of hypophosphatemia caused due to increased levels of FGF23 and associated with low levels of 1,25-(OH)2D [151]. This evidence concerns the gene FGF23 and X-linked hypophosphatemia.