What causes congenital adrenal hyperplasia?

The most common cause of congenital adrenal hyperplasia is a genetic mutation. This occurs when there is a change in the 21-hydroxylase enzyme. The adrenal gland needs 21-hydroxylase to make adequate amounts of hormones. If the body is deficit of 21-hydroxylase, which is also known as 21-hydroxylase deficiency, this can result in decreased cortisol production.