GSTM1 and thalassemia: By contrast, in patients with thalassemia intermedia (TI) -defined as a clinical variant of thalassemia characterized by a thalassemia phenotype of mild-moderate degree of severity- able to maintain Hb levels of 7 g/dl without regular blood transfusion (NTD), iron overload, in addition to the increased absorption, is due to ineffective erythropoiesis.