AD is characterized by two major hallmarks: (i) senile plaques (SP), composed of deposits of the amyloid-β (Aβ) peptide of 39 to 42 aminoacidic residues, generated by the proteolytic excision of the amyloid precursor protein (APP) by β and γ secretases, in the extracellular space [18]; and (ii) neurofibrillary tangles (NFT), derived from the progressive aggregation of hyperphosphorylated tau protein, inside neurons, that derive from tau assembly into oligomeric structures named “paired helical filaments” (PHF). The gene discussed is APP; the disease is Alzheimer disease.