SMAD2 and hydrops fetalis: Among them, SMAD family members, including SMAD2, SMAD3, SMAD4, and SMAD7, have a strong relationship to protein regulation and have been reported and validated to function in the initiation of HF cycling through conventional signaling pathways (Alimperti et al., 2012; Oshimori and Fuchs, 2012; Wang et al., 2017).