In pathological conditions such as type 2 diabetes mellitus, metabolic syndrome, Alzheimer’s and Parkinson’s diseases, the insulin level is increased markedly in blood, while in the brain, on the contrary, it is markedly diminished, which leads to disruption of insulin signaling in the hypothalamus and other regions of the brain [4,5,6,7]. The gene discussed is INS; the disease is Parkinson disease.