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
Cryptic:
(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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