The 21-hydroxylase enzyme encoded by CYP21 has pivotal roles and one of the main steps in adrenal and ovarian steroidogenesis is the conversion of 17-hydroxyprogesterone into 11-deoxycortisol, catalyzed by CYP21. For most cases of congenital adrenal hyperplasia, the deficiency of this enzyme, inherited by an autosomal recessive trait, is a typical sign, subsequently increased serum 17-hydroxyprogesterone levels correlated with its deficiency. Here, CYP21A2 is linked to congenital adrenal hyperplasia.