CYP21A2 and congenital adrenal hyperplasia: Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive disorders of steroid metabolism caused by the deficiency (loss of or severely decreased activity) of one of five steroidogenic enzymes involved in the cortisol biosynthesis: cholesterol side-chain cleavage enzyme (CYP11A1), 3 beta-hydroxysteroid dehydrogenase (HSD3B2), 17 alpha-hydroxylase/17,20 lyase (CYP17A1), 21-hydroxylase (CYP21A2), and 11 beta-hydroxylase (CYP11B1) [1].