CYCS and obesity due to melanocortin 4 receptor deficiency: Similarly, we have observed that the transcription of genes associated with mitochondrial function (cytochrome-c, PPARα, PGC-1α and transcriptional factor A mitochondrial) are decreased in the muscle of older obese adults compared to their lean counterparts (4), thereby suggesting that age and obesity may act as synergistic factors impairing muscle mitochondrial function.