Structural aspects of pathology in Alzheimer's disease.

The characteristic lesions of Alzheimer's disease, neurofibrillary tangles and neuritic plaques, are the sites of accumulation of abnormal fibrillar material. The structure of the paired helical filament from tangles has been analysed by electron microscopy and biochemical studies have shown that it contains microtubule associated protein tau as a component. Fibrils of beta-amyloid in the neuritic plaque arise by polymerization of a small proteolytic fragment of a much larger precursor protein. It is not yet clear what triggers the events that lead to assembly of the abnormal structures nor why the structures once formed are so resistant to turnover.