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. The gene discussed is PPARGC1A; the disease is obesity due to melanocortin 4 receptor deficiency.