However, a patient with Hb Tak and β+-thalassemia (IVS1-5 (G>C)) showed no symptomatic erythrocytosis (Hb 11 g/dL, Hct 37.5%), which might be explained by the underlying disease with an atrial septal defect and failure to thrive. The gene discussed is GSTM1; the disease is thalassemia.