In accordance with their role in anorexic signaling pathways, mutations in the MC4R and POMC genes, which encode the melanocortin 4 receptor and pro-opiomelanocortin, respectively, result in hyperphagia and obesity in humans (Krude et al., 1998; Vaisse et al., 1998; Yeo et al., 1998) and rodents (Challis et al., 2004; Huszar et al., 1997; Yaswen et al., 1999; Yeo and Heisler, 2012). Here, MC4R is linked to obesity due to melanocortin 4 receptor deficiency.