NPY and obesity due to melanocortin 4 receptor deficiency: Sema3A is extensively expressed in the hypothalamus, and it plays a function in axon guidance and neuronal cell migration during the development of the central nervous system, meanwhile, its mutant genes are also considered to be the culprits of obesity, because the paraventricular nucleus and the arcuate nucleus, where Sema3A and its receptors are located, are intimately related to the body’s energy uptake and expenditure, and one of the key factors mediating this is the interaction between neuropeptide Y(NPY) and leptin receptor (OB-R).