GSTM1 and myocardial ischemia: IHD genotypes were re-categorized into 5 groups; i.e., 1) non-IHD (reference group), 2) one α-gene defect (including heterozygous α+-thal and heterozygous Hb CS), 3) two α-gene defects (including heterozygous α0-thal, homozygous α+-thal, and compound heterozygous α+-thal with Hb CS), 4) β-thal carriers (with or without α-thal), and 5) Hb E carriers (with or without α-thal).