INS and obesity due to melanocortin 4 receptor deficiency: This refers to the signaling systems regulated by insulin, leptin, and the agonists of melanocortin (MCR), serotonin (5-hydroxytryptamine, 5-HTR), and dopamine (DAR) receptors, whose impaired activity is associated with hyperphagia, obesity, dyslipidemia, and insulin resistance typical of DM2 and metabolic syndrome [9–13].