Analysis of nitric oxide synthase genes in age–related macular degeneration

Abstract

Abstract: : Purpose: Cigarette smoking is the most consistently identified non–genetic risk factor for age–related macular degeneration (AMD). Other cardiovascular risk factors have also been implicated in this disorder. Smoking, hypertension, and cardiovascular disease have been associated with endothelial dysfunction. Since nitric oxide (NO) regulates endothelial function, genes encoding NO synthases are plausible candidate genes for AMD, particularly the endothelial nitric oxide synthase (eNOS, NOS3). Methods: We have confirmed expression of all three NOS genes in the retina with real–time quantitative RT–PCR. We have genotyped 14 single–nucleotide polymorphisms (SNPs) in NOS1, NOS2A and NOS3 in 162 multiplex and singleton AMD families, an additional 230 AMD patients without sampled relatives, and 196 unrelated controls. All study participants were evaluated by grading of color fundus photographs. Results: A polymorphism in the 5’ region of NOS3 showed significant evidence for association with susceptibility to AMD in family–based association analysis, due to over–transmission of the G allele and specifically the G/G genotype (allelic PDT: p=0.009; genotype PDT: p=0.02). Case–control analysis in individuals with smoking history information indicated that the G/G genotype was significantly more common in AMD patients (63.8%) than in controls (50.4%; p=0.005 adjusted for age and sex). Subgroup analysis revealed an increased risk due to the G/G genotype in "ever" smokers (p=0.003), but not in "never" smokers (p=0.38). Conclusions: The associated SNP is located 7 kb upstream from exon 1 of NOS3 and may be in linkage disequilibrium with a known NOS3 promoter polymorphism (T–786C), which has been associated with early–onset coronary artery disease, both in the general population and specifically in smokers. Thus, our data support the hypothesis that smoking–mediated dysfunction of NO biosynthesis in endothelial cells may play a role in AMD.

Keywords: age–related macular degeneration • candidate gene analysis • gene/expression