From a neuropathological point of view, Alzheimer’s disease (AD) is characterized by the extracellular accumulation of the amyloid β (Aβ) peptides, resulting from the processing of amyloid precursor protein (APP) and the presence of intraneuronal neurofibrillary tangles derived by the hyperphosphorylation of tau protein. The gene discussed is APP; the disease is early-onset autosomal dominant Alzheimer disease.