Endothelial nitric oxide synthase Glu298Asp, 4b/a, and T-786C polymorphisms in type 2 diabetic retinopathy

The possible association between the endothelial nitric oxide (eNOS) gene T-786C (promoter region), 27-bp repeat 4b/4a (intron 4), and Glu298Asp (exon 7) polymorphisms with diabetic retinopathy (DR) was investigated.

A retrospective case-control study.

A total of 872 type 2 diabetes (T2DM) patients were studied, of whom 383 presented with preproliferative/proliferative retinopathy (DR group), and 489 with absent/mild retinopathy (DWR group).

Glu298Asp and T-786C genotyping was carried out by PCR-RFLP analysis, while 4b/4a was assessed by PCR. Genotype distribution was compared using the chi(2)-test, and the contributions of the polymorphisms to DR were analysed by haplotype analysis and multivariate regression analysis.

Lower prevalence of mutant 4a (P = 0.011), and heterozygous 4b/4a (P = 0.042) were seen in the DR compared to the DWR groups; the allele and genotype distribution of the Glu298Asp and T-786C polymorphisms were comparable between DR and DWR groups. Three-loci haplotype analysis demonstrated significant association between eNOS variants and DR, with protective [haplotype 122 (Glu298/4a/-786C)], and susceptible haplotypes [haplotypes 112 (Glu298/4b/-786C) and 222 (Asp298/4a/-786C)] identified. Multivariate regression analysis confirmed the association between haplotypes 122 (P = 0.015); 112 (P = 0.027), and 222 (P = 0.048) and DR, after controlling for potential covariates (including age, sex, age of disease onset; HbA1c; hypertension, total cholesterol).

This study identifies genetic variation at the eNOS locus as genetic risk factor for diabetic retinopathy, which may serve as a useful marker of increased susceptibility to the risk of retinopathy.