Congenital adrenal hyperplasia because of 21-hydroxylase deficiency. A genetic disorder of interest to obstetricians and gynecologists.

Congenital adrenal hyperplasia (CAH) due to deficiency of the enzyme 21-hydroxylase (21-OH), is distinguished in its classical and nonclassical form and is one of the most common autosomal recessive inherited diseases in humans. The classical form appears between 1:5000 and 1:15000 among the live neonates of North America and Europe, whereas the nonclassical form occurs in approximately 0.2% of the general white populations. Three alleles are associated with the 21-OH locus and can be combined in various ways to individuals who are either unaffected, heterozygote carriers, or affected with the classical or nonclassical disease. Variable signs and symptoms of hyperandrogenism are common to both types of the disorder. In women with CAH, hyperandrogenism may be present, extending from virilization of external genitalia and salt-wasting in classical (C)-CAH cases, to menstrual irregularity, obesity, short stature, infertility or subfertility and skin disorders such as hirsutism, in nonclassical (NC)-CAH cases. These clinical characteristics of NC-CAH cases do not differ unmarkedly from those shown in patients with polycystic ovary syndrome, idiopathic hirsutism, or hyperinsulinemia. The significant advances in molecular biology and gene analysis over the past 2 decades have led to the development of novel sensitive methods of DNA analysis and study, including polymerase chain reaction and Southern blot analysis. Thus it has been revealed that the 21-OH gene (CYP21A2) and its nonfunctional pseudogene (CYP21A1P) are located on chromosome 6 (6p21.3), sharing a high homology of about 98%. Inactivating mutations occur as complete gene deletions, large gene conversions and pseudogene-derived mutations.