CYP2R1 loss‐of‐function mutations in humans result in vitamin D–deficiency rickets,(1) and mice with Cyp2r1 deletion show an approximately 50% reduction in serum 25(OH)D concentrations compared with wild‐type mice.(2) 25(OH)D, the most abundant circulating form of vitamin D, can then be converted to 1,25(OH)2D by the action of CYP27B1, the 25‐hydroxyvitamin D‐1α‐hydroxylase [1α(OH)ase] (Fig. 1). This evidence concerns the gene CYP2R1 and rickets.