Patients with anemia (Hb <12 g/dL) did not benefit more from FCM than those without anemia (P value for interaction 0.758), and in the group of patients treated with FCM, no association was discovered between the change in Hb and the change in peak VO2 (for FCM: r=−0.0758, P=0.51) (Figure I in the online-only Data Supplement). The gene discussed is GSTM1; the disease is anemia (phenotype).