Furthermore, we demonstrated that intracerebroventricular (i.c.v.)leptin administration ameliorates hyperglycemia in complete insulin-deficient mice bearing a genetically-engineered gene that allows ablation of almost 100% of pancreatic β-cells; a degree of β-cells deficiency that is not achievable with any other animal model to date (Fujikawa et al., 2013). The gene discussed is LEP; the disease is Hyperglycemia.