The phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway is a key regulator of cell growth and proliferation, and aberrant activation of this pathway promotes the development of obesity.79–81 PI3K and AKT are two major nodes in this pathway, which are activated by upstream signals such as hormones and growth factors. This evidence concerns the gene AKT1 and obesity due to melanocortin 4 receptor deficiency.