LEP and obesity due to melanocortin 4 receptor deficiency: The most fundamental cause of obesity is that energy intake is greater than consumption, and excess energy is stored in the body in the form of fat, resulting in excessive accumulation of body fat [4]; that is, the imbalance between energy storage and consumption is the basis of obesity [5] Leptin is one of the most important energy regulation signals, which is not only present in the blood, but also widely distributed in the brain tissue and gastrointestinal tract.