Several pathways related to the development of leptin resistance have been studied in animal models such as the fat mass and obesity-related gene, oestradiol (E2) and peroxisome proliferator-activated receptor γ, phosphodiesterase-3B (PDE3B)-cAMP- and Akt-pathways of leptin signalling in the hypothalamus [17,18]. The gene discussed is PDE3B; the disease is obesity due to melanocortin 4 receptor deficiency.