KL and Hypercalcemia: Fgf23−/− and Klotho−/− mice suffer from intoxication with 1,25(OH)2D3 due to the lack of FGF23-mediated inhibition of renal 1α-hydroxylase, resulting in hypercalcemia and hyperphosphatemia, which are responsible for the premature aging-like phenotype and the early mortality9, 26.