Studies conducted in humans have shown that CYP2R1 is a good candidate for the enzymatic conversion of vitamin D3 to 25(OH)D3, since patients with a mutation in CYP2R1 have a deficiency of 25(OH)D3 and exhibit signs and symptoms of vitamin D deficiency and develop rickets [147, 148]. Here, CYP2R1 is linked to vitamin D deficiency.