CS and obesity due to melanocortin 4 receptor deficiency: For example, fatty acid oxidation (FAO) and the activity of enzymes involved in mitochondrial fatty acid transport and oxidation, such as carnitine palmitoyltransferase 1 (CPT-1) and citrate synthase (CS), are lower in the skeletal muscle during obesity, and higher intramyocellular lipid (IMCL) content is observed in insulin resistant subjects [18,19].