This is particularly pertinent in the Southeast Asian region, where the disorder co-exists with β-thalassaemia, including the commonest haemoglobin variant, Hb E. Many studies have shown a positive epistatic interaction between α- and β-thalassaemia, whereby their co-inheritance results in the amelioration of the associated blood disorder (Fucharoen and Weatherall, 2012; Viprakasit et al., 2004). This evidence concerns the gene GSTM1 and hematologic disorder.