CLOCK and obesity due to melanocortin 4 receptor deficiency: To adapt to the environmental changes caused by the Earth’s rotation, mammals have developed a circadian biological clock with a period of approximately 24 h.1 Disruption to the circadian rhythms can lead to many suboptimal health conditions and diseases, such as obesity, diabetes, osteoarthritis, and cardiovascular diseases.2–5 The circadian rhythm biological clock consists of a central oscillator and peripheral oscillators.