FGF23 and secondary hyperparathyroidism: Consistent with our prior studies, and despite the “rescue diet,” Cyp27b1 null females had hypocalcemia (Figure 7A), hypophosphatemia (Figure 7B), secondary hyperparathyroidism (Figure 7C), lower FGF23 (Figure 7D), very low calcitriol (99.6 ± 14.1 pmol/L, above the 20 pmol/L detection limit due to fetal-placental sources) (Figure 7E), and higher 25(OH)D3 (Figure 7F).