In cases of congenital adrenal hyperplasia, which enzyme is typically deficient?

Congenital adrenal hyperplasia (CAH) is primarily caused by a deficiency in the enzyme 21-hydroxylase. This enzyme plays a critical role in the adrenal cortex by facilitating the conversion of 17-hydroxyprogesterone to 11-deoxycorticosterone and progesterone to 11-deoxycortisol. When 21-hydroxylase is deficient, there is an accumulation of steroid precursors, particularly 17-hydroxyprogesterone, which can lead to an adrenal crisis and various clinical manifestations, including salt-wasting, virilization, and abnormal hormone levels.

The condition can lead to significant hormonal imbalances that result in a spectrum of symptoms depending on the degree of enzyme activity. Newborns typically present with ambiguous genitalia in females due to excess androgen production and potentially life-threatening adrenal insufficiency in both sexes.

Other enzymes such as 11-hydroxylase, 17-hydroxylase, and 3β-hydroxysteroid dehydrogenase are associated with different types of congenital adrenal hyperplasia, which may have distinct clinical presentations. However, 21-hydroxylase deficiency is the most common and clinically significant form of CAH,