Some of the molecular signals involved in HF regression process have been determined, including fibroblast growth factor (FGF), transforming growth factor-β (TGF-β), tumor necrosis factor-β (TNF-β), Wnt, sonic hedgehog (SHH), neurotrophins (NT), and homeobox proteins [7, 9–13]. The gene discussed is BDNF; the disease is hydrops fetalis.