Alzheimer disease (AD) represents the most common form of dementia in humans, caused by the pathologically relevant accumulation of proteinaceous aggregates, i.e., intracellular MAPT/tau tangles and/or extracellular beta amyloid peptide [Aβ] plaques, which progressively leads to neuronal cell death and decline in cognitive functions. The gene discussed is APP; the disease is Alzheimer disease.