At microscopic examination, the two pathognomonic alterations of AD consist of senile plaques (or amyloid plaques) and neurofibrillary tangles (NFT); the first ones are formed by extracellular aggregation of the amyloid-beta peptide (Aβ), which is over-produced from Amyloid Precursor Protein (APP), whereas the second ones are formed by intracellular deposits of hyperphosphorylated tau-protein at the cytoplasmic level. The gene discussed is APP; the disease is Alzheimer disease.