Alzheimer’s disease (AD) is conceptualized as a progressive consequence of two hallmark pathological changes: extracellular neuritic plaques, which are composed of amyloid-beta (Aβ) surrounded by dystrophic neuritic processes, and neurofibrillary tangles, which are intraneuronal aggregates of insoluble cytoskeletal elements, composed mainly of phosphorylated tau protein. This evidence concerns the gene MAPT and Alzheimer disease.