The adult-onset obesity in the OT and OTR null mice is characterized by increased body weight (Kasahara et al., 2007; Takayanagi et al., 2008; Camerino, 2009), fat mass (Sun et al., 2019) and/or fat pad weight (Takayanagi et al., 2008; Camerino, 2009). The gene discussed is OXTR; the disease is obesity due to melanocortin 4 receptor deficiency.