21-dehydrogenase deficiency (21-OHD) is the most common cause of congenital adrenal hyperplasia (CAH). Some mutations cause less severe enzyme deficiency, resulting in a nonclassical course.

Inheritance: autosomal recessive


Nonclassic forms:

(1) delayed onset

(2) cryptic


Both may only be appreciated while working up family members with classic 21-OHD.


Delayed onset:

(1) normal in neonatal period

(2) mild excess in adrenal androgens that may become apparent later in life

(3) mild elevation of 17-hydroxyprogesterone, which is exaggerated after ACTH stimulation



(1) asymptomatic

(2) excess production of 17-hydroxyprogesterone only occur after ACTH stimulation


Both show biallelic mutations in CYP21A2.


A patient may develop an adrenal incidentaloma.

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