INS and obesity due to melanocortin 4 receptor deficiency: Based on the timing of disease onset, genetic predisposition and clinical phenotype, diabetes has been traditionally classified into two main groups: type 1 diabetes, featured by an autoimmune-mediated targeting of pancreatic beta cells leading to a deficiency in insulin secretion, and type 2 diabetes, tightly associated with obesity and ageing, featured by insulin resistance and chronic inflammation in insulin-sensitive tissues [2].