Pitfalls in molecular diagnosis of 21-hydroxylase deficiency in congenital adrenal hyperplasia.

Congenital adrenal hyperplasia (CAH) is a putative error of metabolism with autosomal recessive heredity pattern. The main manifestations of classic form of CAH are salt-wasting, dehydration and simple virilization in both sexes and ambiguous genitalia in female gender. 21-hyroxylase (CYP21A2) impairment with prevalence value of 1 in 10,000-15,000 live births is the most common etiology of CAH. Because of consanguineous marriages, the frequency of the CAH in Iran is very high. A wide range of mutations diversity exists in CYP21A2 gene and a large number of these mutations derived from a highly homologous pseudogene, CYP21A1P, through gene conversion. In addition, new mutations such as small and large deletion and point mutations can also result in enzyme deficiency. Various methods for mutation detection were performed. The main obstacle in molecular diagnosis of CAH is amplification of pseudogene during polymerase chain reaction of CYP21A2. All attempts focus on discrimination of pseudogene from gene; that is why, there is the majority of mutations on pseudogene, and if we have contamination with the pseudogene, the result will be unreliable. Here, we discuss this methods and advantage and disadvantage of those.