Mutations in OXT or its receptor (OXTR) are directly associated with obesity in animals (Kasahara et al., 2007; Takayanagi et al., 2008; Camerino, 2009; Zhang et al., 2011; Sun et al., 2019) and humans (Wheeler et al., 2013; Qian et al., 2014; Yuan et al., 2016). Here, OXT is linked to obesity due to melanocortin 4 receptor deficiency.