CAH refers to a group of genetic disorders that affect the adrenal glands. These glands sit on top of the kidneys and release hormones the body needs to function. CAH is caused by three disturbances:
CAH can also cause imbalances in the hormone adrenaline (pronounced uh-DREN-uhl-in), which affects blood sugar levels, blood pressure, and the body's response to stress.1,2
The hormone imbalances in most cases of CAH (about 95%) are caused by too little of a substance called 21-hydroxylase (pronounced hahy-DROK-suh-leys). The adrenal glands need 21-hydroxylase to make proper amounts of hormones. This type of CAH is sometimes referred to as 21-hydroxylase deficiency. In CAH due to 21-hydroxylase deficiency, the adrenal glands cannot make enough cortisol or aldosterone. In addition, the glands make too much androgen. People with 21-hydroxylase deficiency also may not produce enough adrenaline.3
About 5% of cases of CAH are caused by deficiency in a substance similar to 21-hydroxylase, called 11-hydroxylase. This type of CAH is sometimes referred to as 11-hydroxylase deficiency. In CAH due to 11-hydroxylase deficiency, the adrenal glands make too little cortisol and too many androgens. This type of CAH does not result in aldosterone deficiency.
Other very rare types of CAH include 3-betahydroxy-steroid dehydrogenase deficiency, lipoid CAH, and 17-hydroxylase deficiency. They are not discussed here.
CAH can be categorized as classic or nonclassic types based on severity:
Figure 1. Position of the adrenal glands and kidneys in the human body.
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