Brain-derived neurotrophic factor has been shown to play an integral role in regulating appetite in both humans (Gray et al., 2006; Marosi and Mattson, 2014) and animals (Kernie et al., 2000; Lebrun et al., 2006), and exogenous administration of BDNF has hypophagic effects (Rios, 2013), while BDNF deletion has hyperphagic effects leading to severe obesity (Gray et al., 2006). The gene discussed is BDNF; the disease is obesity due to melanocortin 4 receptor deficiency.