The “backdoor pathway” also contributes to hyperandrogenism observed in POR deficiency explaining, at least in part, maternal virilization during pregnancy in presence of placental aromatase and virilization of female fetuses, despite postnatal deficiency of sex steroids (12,23,24). This evidence concerns the gene CYP19A1 and congenital adrenal hyperplasia due to cytochrome P450 oxidoreductase deficiency.