APP and Alzheimer disease: Alzheimer's disease (AD) is characterized by a diffuse loss of neurons in the hippocampus, enterorhinal cortex, amygdala, and different regions of the neocortex with extracellular deposition of oligomerized amyloid beta peptide (Aβ42) called amyloid plaques and intraneuronal neurofibrillary tangles composed of phosphorylated tau protein [13].