FGF23 and hypophosphatemia: On a normal diet, Vdr−/− mice were hypocalcemic, hypophosphatemic, had elevated parathyroid hormone (PTH) levels and virtually undetectable fibroblast growth factor (FGF23) levels, while urinary fractional excretion of calcium and phosphate remained relatively high given the hypocalcemia and hypophosphatemia (Fig. 3a, b).