A recent study by Bydon et al. revealed that of 8015 patients who underwent elective craniotomy for malignant tumor resection, 1710 patients (21.4%) were anaemic (anaemia defined by haemoglobin (Hb) value < 11 g/dL for women and <13 g/dL for men). The gene discussed is GSTM1; the disease is anemia.