GSTM1 and asbestosis: Testing the interactions between different genotypes and smoking, GSTM1-null polymorphism was shown to modify the association between smoking and asbestosis (Tables 3 and 4), where an increased risk of asbestosis was found only among ever-smokers who had GSTM1-null genotype (OR = 1.48, P = 0.009) (Table 3).