Distribution of endothelial nitric oxide synthase gene polymorphisms in Turkish population.

Nitric oxide (NO) is the major mediator in the regulation of vascular homeostasis. It is synthesized by endothelium from arginine with the catalytic help of endothelial NO synthase (eNOS). Polymorphisms in the eNOS gene have been associated inconsistently with many vascular diseases. Conflicting results may arise from ethnic variations, notably in control-case studies. Therefore, to obtain reliable information and improve the design of such genetic association studies, we examined the distribution of genetic alleles of 3 clinically relevant eNOS polymorphisms (the variable number of tandem 27-base pair [bp] repeats in intron 4, T-786C in promoter, and G894T in exon 7) in 300 healthy Turkish individuals with a mean age of 50.07 (SD 12.15) years (range, 22-78 years; 50.7% men and 49.3% women). The haplotype frequency was estimated and associations between 3 polymorphisms were evaluated. We discussed the similarity and differences in the distribution of alleles with other populations. The allele frequencies were 45.3%, 48%, and 62.7% for GG of exon 7, TT of promoter, and bb of intron 4 (wild types), respectively. The most common haplotype combines the wild-type alleles (G-T-b) for all 3 polymorphisms (estimated frequency, 37.6%). The linkage analysis between each pairwise combination showed specific associations between T-786C polymorphism in promotor and G894T polymorphism in exon 7 (positive D' value, +0.3387). No significant correlation was found in the genotype distribution of the 3 polymorphisms with age, sex, and obesity. Our eNOS gene allele distributions resemble those of Caucasians and white populations. Our data showed ethnic differences with other populations in the allele distribution of eNOS gene besides conserved distribution of these polymorphisms in Turkish population. This study produced a reference control data for the 3 eNOS polymorphisms in Turkish population and will be helpful in planning eNOS association studies in vascular disease.