CYP21A2 and congenital adrenal hyperplasia: More than 90% of CAH cases are caused by mutant 21-hydroxylase (CYP21A2) (10), a key enzyme in glucocorticoid and mineralocorticoid biosynthesis (Fig. 1); the presence and severity of loss of cortisol and aldosterone production CYP21A2 deficiency is 17OHP, but 17OHPreg, Prog, and Preg are also increased (12).