They are caused by mutations that affect genes that coordinate the synthesis of the globin chains of hemoglobin (Hb), thereby resulting in absence or reduced synthesis (thalassemia and hereditary persistence of fetal hemoglobin) or structural changes (sickle cell disease, Hb C, Hb D and Hb E, among others).1, 2. Here, GSTM1 is linked to thalassemia.