The combined GSTM1 present/GSTT1 null genotype was found to have a limited effect against the development of CML when compared to GSTM1 present/GSTT1 present genotype (OR 95% CI, 0.3, 0.08-0.99; p = 0.049). The gene discussed is GSTM1; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.