PPIB and obesity due to melanocortin 4 receptor deficiency: Many of the proteins identified in the present study that showed increased expression with obesity are predominantly involved in energy utilization, either fatty acid β oxidation (e.g. malonyl-CoA decarboxylase (MLYCD)) or glucose oxidation (e.g. pyruvate dehydrogenase kinase isozyme 4 (PDK4)).