What causes congenital adrenal hyperplasia (CAH)?

CAH is caused by changes (mutations) in one of several genes. These changes lead to deficiencies in 21-hydroxylase or, less commonly, 11-hydroxylase. Both of these are chemicals called enzymes. The adrenal glands need these enzymes to make proper amounts of the hormones: cortisol, aldosterone, androgens, and adrenaline.

Illustration of Autosomal Recessive Disorder shows two carrier parents and four children: one affected child, two carrier children, and one unaffected child. The affected child has a copy of the congenital adrenal hyperplasis (CAH) gene from both parents. The carrier children can either have a copy of the CAH gene from the father and a copy of a normal gene from the mother, or a copy of the CAH gene from the mother and a copy of a normal gene from the father. The unaffected child would have a normal gene from both father and mother.

Figure 2. Inheritance of an autosomal recessive disorder from carrier parents.

How is CAH inherited?

The genes for CAH are passed down from parents to their children. In general, people have two copies of every gene in their bodies. They receive one copy from each parent. For an infant to have CAH, both copies must have an error that affects an adrenal-gland enzyme.

CAH is an example of an autosomal (pronounced AW-tuh-soh-muhl) recessive disorder:

Autosomal means the gene is not on the X chromosome or Y chromosome.
Recessive means that both copies of the gene must have the error for the disease or disorder to occur.

If both parents have CAH, all of their children will also have it. If each parent carries one affected gene and one normal gene (called a "carrier"), there is a one-in-four chance of their child having CAH.