Evidence of progressive marrow failure as manifested by the development of, or worsening of, anemia and/or thrombocytopenia. Cut‐off levels of Hb < 10 g/dL or platelet counts of < 100,000/μL are generally regarded as indications for treatment. However, it should be pointed out that in some patients platelet counts of < 100,000/μL may remain stable over a long period of time; this situation does not automatically require therapeutic intervention. The gene discussed is GSTM1; the disease is anemia (phenotype).