POR deficiency (MIM 613571) due to mutations in the POR gene (MIM 124015) results in an unusual form of CAH first described in 2004, characterized by partially deficient P450c17 activity, with or without associated deficient activity of P450c21 and P450aro (58–60). This evidence concerns the gene CYP17A1 and congenital adrenal hyperplasia due to cytochrome P450 oxidoreductase deficiency.