To date, two types of neurotrophic factors, including brain-derived neurotrophic factor (BDNF) and ciliary neurotrophic factor (CNTF), have been linked to the central control of energy homeostasis, as mutations in the genes encoding BDNF and its receptor tropomyosin receptor kinase B (TrkB) are found in patients with severe obesity (Yeo et al., 2004; Gray et al., 2006; Han et al., 2008), and administration of CNTF protein leads to body weight loss in both human and mice (Miller et al., 1996; Gloaguen et al., 1997). Here, CNTF is linked to obesity due to melanocortin 4 receptor deficiency.