PTH and hyperparathyroidism: Our current study found more severe hypophosphatemia and hyperparathyroidism with enlarged parathyroid glands in 2-week-old double homozygous CaR- and 1α(OH)ase-deficient neonates than in CaR−/− mice, indicating that 1,25(OH)2D3 inhibits parathyroid growth and PTH biosynthesis in a CaR-independent manner.