SIRT1 and obesity due to melanocortin 4 receptor deficiency: Besides longevity extension, SIRT1 has been attributed many beneficial effects in a variety of age-related diseases ranging from metabolic disturbances, such as obesity and diabetes mellitus, especially type 2, as well as cardiovascular, neurodegenerative, pulmonary, renal, musculoskeletal, autoimmune, and skin diseases to cancer [11,33,34,35,36,37,38,39,40,41].