Regarding the xenobiotic system, gene polymorphisms of CYP2E1, GSTM1, NQO1, NAT2, and ABCB1 (MDR1) were more frequently associated with childhood leukaemia risk, which also showed interaction effect with environmental exposures such as paints, household pesticides, insecticides, smoking, alcohol, and trihalomethanes. The gene discussed is CYP2E1; the disease is leukemia.