FGF23 and X-linked hypophosphatemia: Among them, FGF-23-related hypophosphatemic diseases, where elevated levels of FGF-23 inhibit proximal tubular phosphate reabsorption and intestinal phosphate absorption by decreasing serum 1,25-dihydroxyvitamin D (1,25D) are rare, including X-linked hypophosphatemic rickets (XLH) and tumor-induced osteomalacia (TIO) (6, 7).