enlargement of the adrenal glands (adrenal gland) resulting primarily from excessive secretion of androgenic hormones by the adrenal cortex. Congenital adrenal hyperplasia mainly affects infants and is caused by mutations in the genes (gene) for enzymes that catalyze the production of cortisol by the adrenal glands. As a result of decreased cortisol production, there is increased secretion of the anterior pituitary (pituitary gland) hormone corticotropin. The high levels of corticotropin may restore cortisol secretion to near normal; however, they also stimulate the production of androgen and sometimes mineralocorticoids (hormones that stimulate retention of salt and water by the kidneys (kidney)) by the adrenal cortex.

The most common type of congenital adrenal hyperplasia is deficiency of 21-hydroxylase, an enzyme that stimulates one of the last steps in cortisol synthesis. Excess androgen produced to overcome this deficiency during fetal life results in virilization—the development of masculine-appearing external genitalia in newborn girls and precocious sexual development in boys—that becomes prominent as the child grows. There may also be decreased production of aldosterone, which leads to increased urinary excretion of sodium and water and decreased urinary excretion of potassium, resulting in low blood pressure, low serum sodium concentrations (hyponatremia), and high serum potassium concentrations (hyperkalemia). Other, rarer forms of congenital adrenal hyperplasia result in varying degrees of hypertension or lack of sexual development, depending on the particular enzyme that is defective.

Congenital adrenal hyperplasia also occurs in adolescents and adults, in which case it is referred to as late-onset congenital adrenal hyperplasia. In women, it results primarily in excess facial hair growth, decreased frequency or cessation of menstrual periods, and infertility. In contrast, the effects are minimal in men because androgen production by the testes far exceeds adrenal androgen production, even when the latter is excessive.

Patients of any age with congenital hyperplasia are treated (therapeutics) with cortisol or a synthetic hormone with similar properties, such as prednisone; some patients may also require mineralocorticoid treatment.