APP and Alzheimer disease: Definite diagnosis of AD is only obtained at autopsy via the histological quantification of two AD hallmarks: brain amyloid plaques (that consist primarily of amyloid-β (Aβ) peptide that is produced from the proteolytic processing of a transmembrane protein, amyloid precursor protein (APP), by β- and γ-secretases, and intraneuronal neurofibrillary tangles, that consist of tau protein, a microtubule-associated protein that is found predominantly in neurons and is responsible for the stability and assembly of microtubules [3].