PTH and Hypocalcemia: The more complete loss of signaling via Vdr in the Vdr-KO rats than in the Vdr (R270L) rats likely led to more severe hypocalcemia early on, to higher PTH levels (Fig. 2d) and then to tertiary hyperparathyroidism, which normalized the serum calcium level and resulted in calcifications, such renal stones, as shown in Fig. 2f27.