In the FAIR-HF study (observation period: 24 months), which targeted 459 patients with chronic heart failure (NYHA II, III, HFrEF) with Hb 9.5 to 13.5 g/dL + iron deficiency, the iron supplementation group had significantly better results than the placebo group in terms of Patient Global Assessment (p < 0.001), NYHA classification (p < 0.001), and 6-min walking distance (p < 0.001) [13]. The gene discussed is GSTM1; the disease is congestive heart failure.