AKT1 and obesity due to melanocortin 4 receptor deficiency: Lipid intermediates of PI, such as diacylglycerol or phosphatidic acid, are important lipid signaling agents, especially phosphatidylinositol-3,4,5-trisphosphate, which is required for activation of protein kinase B (Akt) involved in cell proliferation [61] and development of obesity and T2D [62].