21-Hydroxylase deficiency: from molecular genetics to clinical presentation.

Congenital adrenal hyperplasia due to deficiency of the enzyme 21-hydroxylase (21-OH), a cytochrome P450 enzyme located in the endoplasmic reticulum and which catalyzes the conversion of 17-hydroxyprogesterone to 11-deoxycortisol and progestene to deoxycorticosterone, is distinguished in its classical and non-classical form and is also one of the most common autosomal recessive inherited diseases in humans. The classical form appears in a rate between 1:5000 and 1:15,000 among the live neonates of North America and Europe, while the non-classical form occurs in approximately 0.2% of the general white population. This rate is especially high between the Ahskenazi Jews and a part (ie Italians, Hispanics) of the Mediterranean populations. Three alleles are associated with the 21-OH locus and can be combined in several ways in individuals who are either unaffected, heterozygote carriers, or affected with classical or non-classical disease. Variable signs and symptoms of hyperandrogenism, such as hirsutism, acne, virilization of the external genitalia and/or the body, short stature, menstrual irregularities, are common to both types of the disorder. Among the genes responsible for the synthesis of the enzyme 21-OH and the antigens of HLA system, exist both a proven genetic linkage and a proven genetic linkage disequilibrium. HLA-Bw47, HLAB5 and HLA-B35 are the most common haplotypes usually met in the classical form, while the haplotype HLA-B14DR1 is the most recurrent in the non-classical form of the disease. The significant advances in molecular biology and gene analysis over the past two decades have led to the development of novel sensitive methods of DNA analysis and study, such as polymerase chain reaction and southern blot analysis. Thus, it has been revealed that the synthesis of enzyme 21-OH is controlled by two genes, the active CYP21B gene and the CYP21A pseudogene. All three forms of the disease have a known sequence of gene changes owing to mutations in isolated proteins or whole series of genes due to translocations or deletions of genetic material.