On admission, he had extreme microcytic anemia with a hemoglobin (Hb) of 1.8 g/dL (normal range 13–17 g/dL) with a mean corpuscular volume (MCV) of 58 fl (normal range 83–101 fL), and hematocrit (Hct) of 8% (normal range 40–50%). The gene discussed is GSTM1; the disease is anemia (phenotype).