Since Cyp24a1 and Vdr double-knockout mice normalized bone formation without impairing bone mineralization, St-Arnaud et al. (32) speculated that a rapid increase in plasma 1,25(OH)2D3 during late gestation in female Cyp24a1 KO mice, resulting in hypercalcemia, affects calcification during development. The gene discussed is VDR; the disease is hypercalcemia disease.