Like all congenital conditions, this appears at birth and is an enlargement of the adrenal glands, which sit just above the kidney. They produce hormones that control the growth of the body, the development of sex organs and the way the body reacts to stress.
Congenital adrenal hyperplasia is sometimes called the adrenogenital syndrome. Infant boys or girls suffer an early onset of male puberty, with an enlarged penis in the boys, a large clitoris in girls and facial hair in both. The body grows rapidly, but at too early a stage the bones stop growing and normal height is not reached.
The basic cause is a genetic defect that prevents the adrenal glands from manufacturing the steroid hormone cortisol. The low level of steroids in the blood causes a gland in the brain (the pituitary) to produce large quantities of a hormone to try to stimulate the adrenal glands to produce more cortisol. Instead, they can only produce large quantities of the male sex hormone.
A diagnosis is made on the basis of how the body looks and the measured levels of hormones in the blood.
Congenital adrenal hyperplasia can be effectively treated by regular doses of the drug hydrocortisone. This is identical to the natural steroid cortisol produced by the adrenal glands, and the presence of it in the blood immediately stops the pituitary gland from sending out too much of its own hormones. Hydrocortisone, or another steroid drug, is given by injection to infants, but later in life can be taken in tablet form by mouth.
In girls, surgery may be necessary along with treatment with hydrocortisone to restore a feminine appearance. Normal menstrual periods and even pregnancy may be possible. In boys, hydrocortisone suppresses the excess male hormone production and allows a normal puberty to occur at the right time.
Because of its genetic origin, the condition cannot yet be prevented, but it is possible to have advice about future pregnancies and how to prevent it happening again.