Angiotensin receptor neprilysin inhibitors (ARNIs) significantly improve the clinical outcome of patients with HFrEF as shown in PARADIGM-HF which compared the angiotensin receptor neprilysin inhibitor (ARNI) (sacubitril/valsartan) with angiotensin converting enzyme inhibitor (ACEI) (enalapril). The gene discussed is ACE; the disease is hydrops fetalis.