Clinicians should start treatment after having discussed with patients the potential harms (e.g., thromboembolism, shorter survival) and benefits (e.g., decreased transfusions) in comparison to the potential harms (e.g., serious infections, immune-mediated adverse reactions) and benefits (e.g., rapid Hb improvement) of transfusions. The gene discussed is GSTM1; the disease is Thromboembolism.