A diagnosis of anemia is based on Hb levels of < 13 g/dL in men and 12 g/dL in women3, and the mean corpuscular volume (MCV) value, defined as the average size of RBCs, can be used to classify anemia as either microcytic, normocytic, or macrocytic4. The gene discussed is GSTM1; the disease is anemia (phenotype).