Oxytocin receptor or OT deficient mice are associated with adult-onset obesity (Kasahara et al., 2007; Takayanagi et al., 2008; Camerino, 2009; Sun et al., 2019) that appears at 8 (Tamma et al., 2009), 10 (Kasahara et al., 2007) or 16 weeks (Camerino, 2009) in OT null mice and 12 weeks in OTR null mice (Takayanagi et al., 2008). This evidence concerns the gene OXT and obesity due to melanocortin 4 receptor deficiency.