MAPT and Alzheimer disease: The relationship between type 2 diabetes and AD may be explained by a number of theories, including hyperglycemia, which causes glutamate-induced excitotoxicity in neuronal cells and insulin resistance in the brain, which may aid in the buildup of amyloid-β, tau phosphorylation, oxidative stress, the formation of advanced glycation end products (AGEs), and apoptosis [20].