What is Congenital Adrenal Hyperplasia?

The adrenal gland sits above each kidney – one on each side of the body. It is made up of a medulla (middle) which makes adrenaline – this part works perfectly normally in CAH. The outer part of the adrenal gland is the adrenal cortex which makes three main hormones called steroids. These steroids are secreted into the blood stream and are necessary for normal health. It is the adrenal cortex and its hormones which are involved in CAH.

Figure 1

The 3 main steroids involved in CAH are:

· Cortisol controls how the body copes with stress, emotional and physical, such as infection or injury. It also helps to control blood sugar levels, raising these levels if they become too low particularly in children.
· Aldosterone helps to regulate the salt levels in the body. Aldosterone causes the kidneys to conserve salt if there is too little salt in the diet, or if a lot of salt is lost due to excessive sweating. Conversely, if a lot of salt is eaten the adrenal cortex reduces the amount of aldosterone secreted, allowing the excess salt to be passed in the urine.
· Androgens are a group of male hormones, one of which is testosterone. For the rest of this booklet the term testosterone will be used to refer to the androgen group. Testosterone is produced by the adrenal cortex in both males and females and they control the formation of pubic hair at the onset of puberty. Testosterone is also produced by the testis and in small amounts by the ovary.

There are five main enzymes in the adrenal gland which convert cholesterol into the important steroid cortisol. If any of these enzymes are missing or defective then not enough cortisol is made for the needs of the body. The body, recognising the low levels of cortisol, will try to stimulate the adrenal cortex to make more by ‘pushing’ the gland harder by a stimulating

hormone called ACTH made in the pituitary gland. The constant unsuccessful stimulation causes the cortex to increase in thickness and become ‘hyperplastic’.

Figure 2

In the most common form of CAH there is a deficiency of an enzyme called 21 hydroxylase. In this form of CAH the production of cortisol and aldosterone is low while testosterone, the male hormone, is produced normally. As the body pushes the adrenal gland harder trying to correct the low cortisol level more and more testosterone is made. In boys, this excess of testosterone causes early sexual development. In females, the excess in testosterone can cause abnormal genital development before birth while in adults it causes irregular periods, unwanted hair growth and acne. Only by correcting the levels of cortisol with substitute therapy does the body recognise normal levels and stop producing excessive amounts of testosterone and the circulating levels become normal.

The hormone disturbances caused by CAH:

Lack of cortisol
Lack of aldosterone
Excessive androgens

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