Identification of frequency and distribution of the nine most frequent mutations among patients with 21-hydroxylase deficiency in Turkey.

Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive disorders mainly due to defects in the steroid 21-hydroxylase (CYP21A2) gene.

Methods: To determine the mutational spectrum in the Turkish population, the CYP21A2 active gene was analyzed in 100 unrelated patients with the classical form of 21-hydroxylase deficiency using PCR and RFLP.

Results: Mutations were detected in 78 patients: 64 patients were homozygous for one mutation, seven patients were compound heterozygous with different mutations on each chromosome, two patients were homozygous for two different mutations, five patients were heterozygous, and 22 patients harbored none of the tested mutations. The most frequent mutation was IVS2-13A/C (28.5%), followed by large gene deletion (17%), Q318X (11.5%), I172N (4%), V281L (3.5%), R356W (3.5%), 8-bp (3%), complex alleles (2%), P30L (1%) and E6 cluster (1%).

Conclusions: The distribution of mutation frequencies in our study was slightly different from those previously reported in Turkey and in other parts of the world.