GRK2 and hydrops fetalis: Three different GRK isoforms (GRK2, GRK5 and, in a minor proportion, GRK3) are present in the heart and also in peripheral blood mononuclear cells (PBMC) (Vinge et al., 2007; Grisanti et al., 2018) and their expression (especially GRK2) changes as a consequence of the hemodynamic alterations that occur in HF or hypertension (Iaccarino et al., 2005; Penela et al., 2006; Vinge et al., 2007; Izzo et al., 2008; Cohn et al., 2009; Santulli et al., 2011, 2013; Piao et al., 2012; Grisanti et al., 2018).