GSTM1 and chronic obstructive pulmonary disease: Significant associations (p < 0.05) with the risk of COPD were found with EPHX T113C, GSTP1, GSTM1, GSTT1, CAT C262T, CYP1A1 MspI, SOD2 Val 9 Ala, SOD3 A213G and HO-1 (Table 2).