However, some hBTh individuals may display mild anemia, characterized by hypochromic and microcytic red blood cells, elevated levels of hemoglobin (Hb) A2, and variable increases in Hb F. In some cases, hBTh may manifest a variety of symptoms including headache, lethargy, fatigue, dizziness, and exercise intolerance, despite having hemoglobin levels within the normal range [4,8]. The gene discussed is GSTM1; the disease is anemia (phenotype).