In FAIR-HF (Ferinject Assessment in patients with IRon deficiency and chronic Heart Failure trial), 459 HF participants in NYHA functional class II or III, with LVEF ≤ 40–45%, ID (defined as ferritin of either < 100 μg/L, or between 100 and 299 μg/L if TSAT < 20%) and a Hb concentration of 95–135 g/dL, were randomised in a 2:1 ratio to either IV FCM or saline and followed up for 24 weeks. The gene discussed is GSTM1; the disease is hydrops fetalis.