Congenital adrenal hyperplasia (CAH) refers to any of several autosomal recessive diseases resulting from mutations of genes for enzymes mediating the steps of biosynthesis of cortisol from cholesterol in the adrenal glands, also known as steroidogenesis. 21-hydroxylase deficiency, also known as CYP21 deficiency or CAH1, is an autosomal recessive disorder that accounts for the vast majority of cases of CAH. This deficiency affects cells in the adrenal cortex of the adrenal glands, and due to the deficiency in an enzyme used in many pathways. This prevents the completion of several hormone biosynthesis pathways, including those producing aldosterone and cortisol, and leads to a buildup of their precursors, including 17a-hydroxypregnenolone, which are then processed by the pathways that produce androgen hormones including testosterone. This disorder can vary in severity, depending on the amount of functional enzyme present. The most severe form is known as the salt-wasting form of 21-hydroxylase, and is caused by a complete lack of functional enzyme. This form is called the salt-wasting form, as the lack of aldosterone produced leads to high levels of sodium excreted in the urine, causing infant blood volume to decrease. High potassium levels in blood are also often observed, but if properly diagnosed, saline solution and hydrocortisone can restore normal blood levels and sodium content. In addition, males are typically visually unaffected, but females often possess ambiguous genitalia due to the excess exposure to testosterone during development. The second most severe form is known as the simple virilising form, which does not involve the salt loss of the salt-wasting form, due to a partially functional 21-hydroxylase enzyme. However, the androgen hormones build up similarly, leading to females with some amount of virilisation, or some amount of male characteristics, including ambiguous genitalia. The third and least severe form, known as the non-classical or late onset form, has the highest function in 21-hydroxylase enzymes, and leads to the smallest buildup of androgen hormones. This means that females exhibit little to no virilisation at birth, but as they age can experience male-associated hair growth and baldness, as well as decreased fertility and menstruation irregularities. It can also lead to an early puberty in both males and females, though treatment can help prevent this if it is caught in time.

21-Hydroxylase Deficiency (CYP21) References