What types of congenital adrenal hyperplasia are there?
Cortisol is an adrenal steroid hormone necessary for life; production begins in the second month of fetal life. Inefficient cortisol production results in rising levels of ACTH, which in turn induces overgrowth (hyperplasia) and overactivity of the
steroid-producing cells of the adrenal cortex. The defects causing adrenal hyperplasia are congenital (i.e., present at birth).
Cortisol deficiency in CAH is usually partial, and not the most serious problem for an affected person. Synthesis of cortisol shares steps with synthesis of mineralocorticoids such as aldosterone, androgens such as testosterone, and estrogens such as estradiol. The resulting excessive or deficient production of these three classes of hormones produce the most important problems for people with CAH. Specific enzyme inefficiencies are associated with characteristic patterns of over- or underproduction of mineralocorticoids or sex steroids.
In all its forms, congenital adrenal hyperplasia due to 21-hydroxylase deficiency accounts for about 95% of diagnosed cases of CAH. Unless another specific enzyme is mentioned, "CAH" in nearly all contexts refers to 21-hydroxylase deficiency. Congenital adrenal hyperplasia (CAH) is an inherited group of disorders which involves any one of the enzymes necessary for the manufacture of cortisol by the adrenal glands. The symptoms of CAH depend on the particular enzyme deficiency. In more than 90 per cent of cases, the steroid 21 hydroxylase is the defective enzyme involved; 21 hydroxylase deficiency or 'classic CAH' is the name given to the most common presentation of the disorder. The effect of this defective enzyme is a blockage in the production of cortisol, overproduction of androgens and, in approximately 75 per cent of cases, an inability to produce the sodium-regulating hormone, aldosterone.
Severe 21-hydroxylase deficiency causes salt-wasting CAH, with life-threatening vomiting and dehydration occurring within the first weeks of life. Severe 21-hydroxylase deficiency is also the most common cause of ambiguous genitalia due to prenatal virilization of genetically female (XX) infants. Moderate 21-hydroxylase deficiency is referred to as simple virilizing CAH; and typically is recognized by causing virilization of prepubertal children. Still milder forms of 21-hydroxylase deficiency are referred to as non-classical CAH and can cause androgen effects and infertility in adolescent and adult women.