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Congenital adrenal hyperplasia due to 3β-hydroxysteroid dehydrogenase deficiency is an uncommon form of congenital adrenal hyperplasia resulting from a mutation in the gene for one of the key enzymes in cortisol synthesis by the adrenal gland, 3β-hydroxysteroid dehydrogenase type II. As a result, higher levels of 17α-hydroxypregnenolone appear in the blood with adrenocorticotropic hormone challenge, which stimulates adrenal corticosteroid synthesis.
There is a wide spectrum of clinical presentations of 3β-HSD CAH, from mild to severe forms. The uncommon severe form results from a complete loss of enzymatic activity and manifests itself in infancy as salt wasting due to the loss of mineralocorticoids. Milder forms resulting from incomplete loss of 3β-HSD type II function do not present with adrenal crisis, but can still produce virilization of genetically female infants and undervirilization of genetically male infants. As a result, this form of primary hypoadrenalism is the only form of CAH that can cause ambiguous genitalia in both genetic sexes.