Bone marrow insufficiency (leukopenia < 4000/μl, Hb < 10 g/dl, thrombocytopaenia > 100,000/μl) serum creatinine > 1.3 mg/dl (115 uM), malignancies, hepatitis B or C or HIV positivity, pregnancy or breast feeding, inadequate contraception, chronic liver disease or alcohol abuse, active gastric ulcer, lack of compliance, further coexisting autoimmune diseases or treatments interfering with the MTX/LEF medication. The gene discussed is GSTM1; the disease is hepatitis B virus infection.