After adjusting for various covariates like age, sex and smoking status, there was an associated risk between GSTT1(−) null individuals and GOLD severity in COPD patients (AOR = 3.33, 95% CI = 1.42–7.81, P = 0.005) However, no association was found between GSTM1(−) and GOLD severity of airway limitation in COPD cases (Table 5). Here, GSTM1 is linked to chronic obstructive pulmonary disease.