Numerous studies of skeletal muscle biopsies from adults with obesity report not only reduced activities of key mitochondrial enzymes including citrate synthase, malate dehydrogenase, NADH oxidase, succinate oxidase and cytochrome oxidase, but also that reduced activity of these enzymes correlates with measures of insulin resistance.7, 8, 9, 10, 11, 12. Here, CS is linked to obesity due to melanocortin 4 receptor deficiency.