INS and obesity due to melanocortin 4 receptor deficiency: Changes in the metabolic pathways of adipocytes in obesity, including adipogenesis and fatty acid esterification, result in the accumulation of free fatty acids and fatty intermediate metabolites in adipocytes (Lipina et al., 2013), reduction of adipocyte sensitivity to insulin, and inhibition of insulin signal transduction (Rao et al., 2013), leading to impaired insulin sensitivity (Heinonen et al., 2015).