Congenital Adrenal Hyperplasia: 11β-Hydroxylase Deficiency

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Abstract
The most potent corticosteroids are 11β-hydroxylated compounds. In humans, two cytochrome P450 isoenzymes with 11β-hydroxylase activity, catalyzing the biosynthesis of cortisol and aldosterone, are present in the adrenal cortex. CYP11B1, the gene encoding 11β-hydroxylase (P450c11), is expressed in high levels in the zona fasciculata and is regulated by adrenocorticotropic hormone (ACTH). CYP11B2, the gene encoding aldosterone synthase (P450c11Aldo), is expressed in the zona glomerulosa under primary control of the renin-angiotensin system. The substrate for P450c11 is 11-deoxycortisol. Mutations in CYP11B1 cause congenital adrenal hyperplasia (CAH) due to 11β-hydroxylase deficiency. This disorder is characterized by androgen excess and hypertension and is autosomal recessively inherited. Classical and nonclassical forms of 11β-hydroxylase deficiency can be distinguished. Studies in heterozygotes for classical 11β-hydroxylase deficiency show inconsistent results with no or only mild hormonal abnormalities (elevated plasma levels of 11-deoxycortisol after ACTH stimulation). Molecular genetic studies of the CYP11B1 gene in 11β-hydroxylase deficiency have led to the identification of several mutations. Transfection experiments showed loss of enzyme activity in vitro. Molecular genetic studies have practical importance for the prenatal diagnosis of virilizing CAH forms.

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