Interestingly, studies examining WAT of monozygotic twin pairs who are lean or obese have revealed a decrease in mitochondrial DNA and PGC1α and OXPHOS protein, correlating an increase in genes associated with inflammatory pathways and thus suggesting a decrease in mitochondrial function as a response to obesity (43 , 49, 132). This evidence concerns the gene PPARGC1A and obesity due to melanocortin 4 receptor deficiency.