CYP17A1 and congenital adrenal hyperplasia due to cytochrome P450 oxidoreductase deficiency: Diagnosis of POR deficiency relies on the detection of a combined impairment of CYP21A2 and CYP17A1 activities, resulting in a combined mild elevation of pregnenolone, progesterone, 17-hydroxypregnenolone, 17-OHP and DOC, with variable cortisol response to ACTH.