Laboratory investigation revealed erythrocytosis (Hb 15.1 g/dl, Hct 57.4%, RBC 7.8 × 1012/L, MCV 73.9 fL) and leukocytosis (42.8 × 109/L), but normal platelet count (157 × 109/L). The gene discussed is GSTM1; the disease is polycythemia.