Classic 21-dehydrogenase deficiency (21-OHD) is the most common cause of congenital adrenal hyperplasia (CAH).
Inheritance: autosomal recessive
Clinical features of classic 21-OHD:
(1) virilization, which may be present at birth
(2) variable salt-wasting (associated with mineralocorticoid deficiency)
(3) variable precocious puberty
Laboratory findings:
(1) hyponatremia and hyperkalemia
(2) elevated serum 17-hydroxyprogesterone (17-OHP), especially after ACTH stimulation (250 µg IV bolus cortrosyn)
(3) elevated adrenal androgens
(4) decreased serum cortisol
(5) biallelic pathogenic variants in CYP21A2
