GSTM1 and sickle cell disease: Haemoglobinopathies are caused by mutations in the two globin gene clusters and are characterised by a reduced or absent synthesis of globin chains in the case of the thalassaemia syndromes, mainly α- and β-thalassaemia, or by defects in the Hb protein structure in the case of structural Hb variants, such as the Hb S that causes sickle-cell disease.