The T-786C and C774T endothelial nitric oxide synthase gene polymorphisms independently affect the onset pattern of severe diabetic retinopathy

Genetic factors could be implicated in the pathogenesis of severe diabetic retinopathy (DR). Recently, we reported a strong association between the eNOS4b/a endothelial nitric oxide synthase (eNOS) polymorphism and severe DR. To examine whether T-786C and C774T eNOS polymorphisms are involved in severe DR, 254 Caucasians with longstanding C-peptide-negative type 1 diabetes, 128 patients with absent/mild DR (control group), and 126 patients with preproliferative/proliferative DR (study group) were genotyped. The distribution of T-786C and C774T eNOS polymorphisms was in Hardy-Weinberg equilibrium and did not differ between the study and control groups. However, in case patients (n = 126), T-786C and C774T polymorphisms influenced the onset pattern of severe DR (P = 0.0169 and P = 0.0257, respectively). The C-786C genotype was associated with early-onset severe DR (duration of diabetes: 15.2 ± 5.9 vs. 19.4 ± 6.3 years, P = 0.0105), and the homozygous T774T genotype was associated with late-onset severe DR (24.3 ± 7.0 vs. 18.4 ± 6.2 years, P = 0.0067). In the case of patients with high glycosylated hemoglobin levels (HbA1c >8%, n = 88), the association between the T-786C polymorphism and early-onset severe DR was stronger (P = 0.0068). Case patients carrying the C-786C genotype had higher HbA1c values (9.61 ± 1.89%) than those carrying the T-786T genotype (8.93 ± 1.47%, P = 0.0173). Multivariate analysis showed that T-786C polymorphism was the best independent factor for onset pattern of severe DR (P < 0.001). These findings, supported by previous associations between eNOS4b/a polymorphism and DR, suggest that T-786C and C774T eNOS polymorphisms affect the onset pattern of severe DR.