The orexins (OX-A and OX-B), also named hypocretins (Eriksson et al., 2001; Messina et al., 2014b), are neuropeptides with critical functions in energy balance and obesity, and therefore in the accumulation of adipose tissue (Tsuda et al., 2002; Monda et al., 2008a). The gene discussed is HCRT; the disease is obesity due to melanocortin 4 receptor deficiency.