NPY and obesity due to melanocortin 4 receptor deficiency: In fact, a Y2R silent mutation in a Swedish population has been associated with resistance to obesity,128 whereas a gain-of-function polymorphism in the NPY gene seems to predispose to individual hyperlipidemia, atherosclerosis, and severe complications of T2D.129 Taken together, these findings further support the metabolic impact of the SNS in the control of energy homeostasis.