CYP21A2 and classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency: The data, therefore, suggest that these C11-oxo C21 steroids would be the predominant metabolites, which is of particular relevance in congenital adrenal hyperplasia (CAH) caused by mutations in cytochrome P450 21A2 (CYP21A2), resulting in 21-hydroxylase deficiency (21OHD).