CLOCK and obesity due to melanocortin 4 receptor deficiency: Since circadian clock genes are regulators of circadian rhythm that modulate the expression of Peroxisome Proliferator-Activated Receptor (PPAR), which is a family of transcription factors involved in cellular lipid metabolism (lipolysis and lipogenesis) (35), high-fat diets can disrupt the circadian modulation of metabolic factor expression in peripheral tissues, causing obesity.