Silent brain infarction (SBI), a unique cerebrovascular disorder, is frequently detected on magnetic resonance imaging (MRI) of apparently healthy elderly persons, and it is known to increase the risk of stroke and other related diseases. Although detailed mechanisms of SBI pathogenesis have yet to be determined, recent studies suggest that SBI is significantly influenced by genetic factors. In this study, we investigated polymorphisms in the endothelial nitric oxide synthase (eNOS) gene (i.e., −786T>C, 4a4b and 894G>T) as possible risk factors for SBI. We enrolled 269 patients with SBI and 234 control subjects and examined their fasting plasma homocysteine and folate levels, and analyzed for eNOS polymorphisms and haplotypes. The prevalence of SBI was shown to be significantly higher in patients with the eNOS 894GT genotype (OR, 2.00; 95% CI, 1.30-3.08) and 894GT+TT genotype (OR, 2.05; 95% CI, 1.34-3.16), compared with the 894GG genotype. However, in the case of −786T>C and 4a4b polymorphisms, no significant difference was observed between SBI patients and normal subjects. Interestingly, we found that the prevalence of SBI can increase twice as high when either −786T>C or 4a4b polymorphism was combined with 894G>T polymorphism, −786TC+CC/894GT+TT (OR, 3.83; 95% CI, 1.24-11.80) and 4a4b+4a4a/894GT+TT (OR, 4.08; 95% CI, 1.34-12.40), respectively. According to haplotype analysis, we found that three haplotypes (−786T-4b-894G, −786T-4b-894T and −786C-4a-894T) were shown to be significantly different between SBI patients and control subjects. These results indicate that eNOS polymorphisms and haplotypes serve as risk factors for SBI, and three different polymorphic loci in the eNOS gene play interactively, thereby leading to synergistic effects for the generation of SBI.

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