Interaction Between T-786C Mutation In ENOS Gene And Environmental Factors In Premature Coronary Heart Disease

Background: Coronary heart disease (CHD), as a kind of cardiovascular disease, can do great harm to human health and quality of life, it is also a leading cause of death and burden of disease in China and most other countries. And, in recent years the incidence and mortality rate of CHD in China has been going up.CHD is a multi-factorial disease, which is related to both the genetic and environmental factors. Gene-gene and gene-environment interaction makes great contribution to the risk of CHD. With the advance of Human Genome Project, it has become more and more popular in medical fields to clarify the pathogenesis of CHD at gene level, especially premature CHD (p-CHD).Endothelial nitric oxide synthase (eNOS), as a key enzyme catalysing the synthesis of nitric oxide (NO) in cardiovascular system, has been much concerned recently. It has been shown that eNOS gene knockout accelerates atherosclerosis in animal models, and gene transfer of eNOS can improve relaxation of carotid arteries from diabetic rabbits. Therefore, mutations in eNOS gene may affect the function and activity of eNOS protein, and it has been considered as a candidate gene for CHD.In recent years, studies have suggested that the T-786C mutation in 5'-flanking region of eNOS gene, which can significantly affect eNOS gene expression, has been associated with CHD and myocardial infarction (MI). However, reports are extremely rare presently on the association between the T-786C mutation in eNOS gene and p-CHD in the Han nationality of China, and the interaction between the T-786C mutation and environmental factors.Objective: To explore the association between the T-786C mutation in eNOS gene and p-CHD; and further to explore and assess the interaction effect between the T-786C mutation and environmental factors on p-CHD and the dose-effect relationship of the interaction.Methods: A hospital-based case-control study was conducted. Newly-diagnosed CHD patients were recruited as study subjects. 188 CHD patients diagnosed at or before age 55 for males and 65 for females were assigned to p-CHD case group with other 315 CHD patients as the control group. Polymerase chain reaction with Mspl restriction enzyme digestion was performed to detect the T-786C mutation in eNOS gene. Univariate test and multiple logistic regression models were used to analyze the association between the T-786C mutation in eNOS gene and p-CHD. Interaction coefficients (γ,γ=β_eg/β_e) were calculated to determinate whether the T-786C mutation in eNOS gene and environmental factors show an interaction in p-CHD, and to assess the dose-effect relationship of the interaction.Results:1. eNOS gene T-786C mutation was significantly associated with p-CHD. There was no significant difference in T-786C mutant genotypes between p-CHD group (TT, TC and CC were 72.34%, 26.06% and 1.20% respectively) and control group (TT, TC and CC were 80.32%, 18.73% and 0.95% respectively) (P=0.105). However, mutant genotypes (TC+CC) in p-CHD group were significantly higher than those in control group (P=0.039). Mutant C allele frequency in p-CHD group was also significantly higher than that in control group (14.63% versus 10.32%, P=0.041, OR=1.489, 95%CI: 1.014-2.187). Stepwise multiple logistic regression analysis at 0.05 significant level with sex, smoking, alcohol drinking, systolic blood pressure (SBP), diastolic blood pressure (DBP), body mass index (BMI), triglyceride (TG) and total cholesterol (TC) covariates indicated that the T-786C mutation still had significant effect on p-CHD (P=0.003, OR=2.04S, 95%CI: 1.269-3.302). 2. The interaction existed in eNOS gene T-786C mutation and smoking, BMI and TG, all showing a hypo-multiplicative model. And the dose-effect relationship all suggested a low exposure-gene effect.3. The interaction existed in eNOS gene T-786C mutation and alcohol drinking, also showing a hypo-multiplicative model. However, the dose-effect relationship suggested a high exposure-gene effect.4. The interaction existed in eNOS gene T-786C mutation and DBP, showing a hypo-multiplicative model. Before potential confounding factors adjusted, the dose-effect relationship suggested a low exposure-gene effect. However, after potential confounding factors adjusted, the dose-effect relationship suggested a high exposure-gene effect.Conclusions:1. The T-786C mutation in eNOS gene might serve as a major risk factor to p-CHD in the Han nationality of China.2. There exist multiplicative model interactions of different degrees between eNOS gene T-786C mutation and environmental factors such as smoking, alcohol drinking, DBP, BMI and TG in the present study population. Also, the dose-effect relationships of the interaction show different types of exposure-gene effect. Coexistence of the T-786C mutation and any of the above-mentioned environmental factors would result in marked increase in the risk of p-CHD.