A nine-month-old Chinese girl presented with one-week history of pallor at a referral hospital where she received a red blood cell transfusion for severe anemia (Hb 3.4 g/dL) and started to treat for iron-deficiency anemia (IDA) after microcytosis (mean corpuscular volume 74.6 fl), hypochromia (mean cell Hb 21.5 pg), and low serum iron concentration (1.28umol/L) were confirmed. The gene discussed is GSTM1; the disease is Iron deficiency anemia.