APP and Alzheimer disease: AD is a clinically neurodegenerative disease characterized by the neuritic plaques resulting from the accumulation of amyloid-beta peptide (Aβ) and neurofibrillary tangles formed by hyperphosphorylated tau in the brain—the histopathological hallmarks that occur early in the hippocampus and entorhinal cortex and spread to other brain regions as the disease progresses [80].