GSTM1 and hemoglobinopathy: It has been estimated that in the WHO Western Pacific Region less than four percent of the population carry a Hb disorder [27] while a later study of schoolchildren in a different province of northern Vietnam found the prevalence of hemoglobinopathy (reporting totaled figures for HbA2, HbAE and HbF, others not tested for) to range between 3.8 and 9.3% [28].