After omitting one study [27] which was spotted by Galbraith plot as the major sources of heterogeneity, the interaction between the GSTM1 null genotype and smoking on CHD risk was also statistically significant (OR = 1.27, 95% CI: 1.08, 1.50; I2 = 0%, P=0.553) (Figure 5). Here, GSTM1 is linked to coronary artery disorder.