Furthermore, brain-specific deletion of Bdnf (Rios et al., 2001), deletion of dendritic BDNF mRNA (Liao et al., 2012), shRNA-mediated knockdown of BDNF using a viral vector (Unger et al., 2007), and a hypomorphic allele of Trkb that expresses only a quarter of TrkB all result in hyperphagia, obesity, and metabolic imbalances such as hyperglycemia (Xu et al., 2003). The gene discussed is BDNF; the disease is obesity due to melanocortin 4 receptor deficiency.