Cytochrome P450 17A1 (CYP17A1) belongs to the cytochrome P450 family; it plays a role in the conversion of pregnenolone and progesterone into their 17-alpha-hydroxylated products and subsequently to dehydroepiandrosterone (DHEA) and androstenedione. CYP17A1 also catalyzes both the 17-alpha-hydroxylation and the 17,20-lyase reaction. CYP17A1 is involved in sexual development during fetal life and at puberty. Defects in CYP17A1 are the cause of adrenal hyperplasia type 5 (AH5). AH5 is a form