PTH and hyperphosphatemia: Hypocalcemia is associated with low FGF23 levels as a study of Gcm2−/− mice characterized by hypocalcemia, hyperphosphatemia, and low calcitriol and PTH levels and Cyp27b1−/− mice with hypocalcemia, hypophosphatemia, and low 1,25(OH)2D3 but high PTH levels has revealed [19].