Genetics of congenital adrenal hyperplasia and genotype-phenotype correlation.

Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency is caused by mutations in the CYP21A2 gene, located on the short arm of chromosome 6. The two main underlying mechanisms of CYP21A2 defects are large gene deletion and conversion. Anticipation of the phenotypes associated with different combinations of CYP21A2 mutations remains the most important determinant in prenatal diagnosis and counseling of the expectant couple who are determined to be at risk for congenital adrenal hyperplasia.