FGF23 and autosomal recessive hypophosphatemic rickets: Examples of human disorders associated with elevated intact FGF23 are ADHR with a defective cleavage site of FGF23, X-linked hypophosphatemic rickets (XLH), and autosomal recessive hypophosphatemic rickets 1 (ARHR1) caused by overproduction of FGF23 in bone, and tumor-induced osteomalacia caused by FGF23-producing tumors (12).