APP and Alzheimer disease: The hallmarks of AD are the presence of extracellular amyloid plaques in the brain formed by β-amyloid-40 (Aβ40) and β-amyloid-42 (Aβ42) peptides which are the product of proteolytic cleavage of the Amyloid Precursor Peptide (APP) peptide fragments; the flame-shaped neurofibrillary tangles of the microtubule-binding protein tau in the lesions [294,296].