21-Hydroxylase deficiency accounts for more than 90% of cases of CAH. The prevalence of this autosomal recessive disorder is 1 in 10,000 births. This deficiency will result in an accumulation of the sex steroids.
In severe cases, a female is born with ambiguous genitalia resulting in incorrect gender assignment. This is caused by androgen excess resulting from the loss of cortical negative feedback on ACTH secretion. A few days after birth vomiting and dehydration occur as a direct result of cortisol and aldosterone deficiency. The condition may be fatal unless it is rapidly diagnosed and treated with steroid replacement. A male patient will present with vomiting and dehydration but without significant genital changes. In less severe cases of 21-hydroxylase deficiency the patient will present in childhood or puberty with signs of androgen excess.
The most important part of the initial treatment is to rehydrate the patient with intravenous saline and to replace the corticosteroids. Once the patient is stable, the glucocorticoids are given orally and sometimes mineralocorticoids (fludrocortisone) are given.
Cortisol is given (10-50mg daily) with a slightly higher dose in the evening to suppress the overnight rise in ACTH levels.
In post-pubertal cases, the long acting corticosteroid analogue (dexamethasone) provides effective ACTH suppression. (Dexamethasone is contraindicated in young children).
Patients are also advised to increase their glucocorticoid dose in times of stress and illness as they face the same potential hazards as those patients with adrenocortical deficiency - i.e. Addison's disease (see Adrenal Insufficiency section).
Plastic surgery to the genitalia is also sometimes required.