Objectives: A rapid and convenient approach for the detection of the most common CYP21 gene mutations in patients with congenital adrenal hyperplasia (CAH) with classical forms of 21-hydroxylase deficiency was used. In addition, a new semiquantitative strategy for the detection of del8-bp was designed. These procedures were used for prenatal diagnosis and genotype-phenotype correlation in northeastern Iran. Design: Molecular analysis of the CYP21 gene for the detection of the 9 most common mutations (CYP21gene deletio n, P30L, i2g, del-8bp, I172N, E6 cluster, V281L, Q318X and R356W) was performed on 30 CAH patients and for prenatal diagnosis in 2 cases. Methods: Restriction fragment length polymorphism, amplification-created restriction sites, allele-specific polymerase chain reaction (PCR) and semiquantitative PCR were performed. Results: We characterized 90% of the CAH chromosomes. The most frequent mutations in the CYP21 gene were del-CYP21 (25%), I172N (22%) and i2g (15%). Unlike in other ethnic groups, there was no R356W mutation, however, a higher rate of del-8bp (10%) was found in our population. Wealso found 6 complex alleles in our patients. For 2 families prenatal CYP21 gene analysis resulted in the diagnosis of healthy fetuses and termination of dexamethasone treatment in the 15th week of gestation. Genotype-phenotype correlation was observed. The rate of homozygosity (50%) was greater than the predicted values due to the higher rate of parental consanguinity in our population. Conclusions: These molecular procedures proved to be sensitive and rapid for the detection of the most common mutations of the CYP21 gene and prenatal diagnosis. Increased 17-hydroxyprogesterone, found in neonatal CAH screening, can be confirmed by these mutation analyses.

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