Furthermore, HF is associated with sympathetic overactivation and Renin-Angiotensin-Aldosterone System (RASS) hyperactivity (37); T3 restores autonomic balance in heart failure by: (1) Attenuating sympathetic overactivation through downregulation of myocardial β adrenergic receptor density and reduction of circulating norepinephrine levels (38); (2) Recovering baroreflex function via upregulation of neuronal nitric oxide synthase (nNOS) in the nucleus tractus solitarius (39), thereby mitigating these detrimental neurohormonal axes (40). The gene discussed is REN; the disease is hydrops fetalis.