FGF23 and hypophosphatemia: FGF-23 was first identified in families with autosomal dominant hypophosphatemic rickets (ADHR) (41), associated with missense mutations in FGF-23 at positions 176 or 179 (R176Q/W and R179Q/W) that render this peptide cleavage resistant and thus increase the intact portion of FGF-23 (iFGF-23), which is the biologically active peptide and thus result in hypophosphatemia (41).