GSTM1 and Beta-thalassemia: Beta thalassemia is usually identified in the laboratory by the observation of Hb A2 greater than 3.5%, although, sometimes, when there is an association with iron deficiency or coinheritance with α- or δ-thalassemia or depending on the type of mutation in the β-globin gene, the Hb A2 can be detected in the normal concentration [15,31].