CYP2D6 and hyperinsulinemic hypoglycemia, familial, 4: CYP2D6 is a potential 25 hydroxyvitamin D-1 α-hydroxylase, which converts vitamin D3 into 25OHD, and vitamin D 25-hydroxylase deficiency resulted in vitamin D deficiency.Human 25-hydroxyvitamin D-1 α-hydroxylase mutations also cause vitamin D-dependent rickets type 1.