 The 17α-hydroxylase activity of CYP17A1 is required for the generation of glucocorticoids such as cortisol, but both the hydroxylase and 17,20-lyase activities of CYP17A1 are required for the production of androgenic and oestrogenic sex steroids by converting 17α-hydroxypregnenolone to dehydroepiandrosterone (DHEA).Mutations in this gene are associated with isolated steroid-17α-hydroxylase deficiency, 17α-hydroxylase/17,20-lyase deficiency, pseudohermaphroditism, and adrenal hyperplasia.Furthermore, the 17,20-lyase activity is dependent on cytochrome P450 oxidoreductase (POR) cytochrome b5 (CYB5) and phosphorylation.