Although the brain's insulin signaling is primarily considered independent due to the predominant presence of GLUT-1 and GLUT-3 over insulin-sensitive GLUT-4 [118], recent findings have highlighted a strong linkage between insulin resistance and cognitive impairments in diseases like MCI [119] and Parkinson’s Disease (PD) [120], with abnormalities in insulin receptor expression and AKT signaling. The gene discussed is SLC2A3; the disease is Parkinson disease.