Figure 1. Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency. In a person with normal adrenal function (left), the adrenal gland produces both cortisol and androgen. The hypothalamic-pituitary-adrenal axis is controlled by negative feedback. In the untreated patient with CAH (middle), a block in cortisol biosynthesis leads to a buildup of cortisol precursors and lack of negative feedback. Corticotropin (ACTH) is oversecreted, and adrenal hyperplasia occurs. The combination of accumulated cortisol precursors and increased ACTH results in massive androgen production. In the treated patient with CAH (right), exogenous hydrocortisone replacement reduces androgen production. Supraphysiologic doses of hydrocortisone are often necessary to adequately suppress androgen production. CRH = corticotropin-releasing hormone.

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