Alzheimer's Disease is a chronic, progressive, degenerative disease of the brain. It is the most common form of dementia.
The exact cause of Alzheimer's Disease is unknown. Age seems to be the most important risk factor, but Alzheimer's Disease destroys brain cells, which is not a normal part of aging. The characteristic findings in Alzheimer's disease are the presence of abnormal clumps (neuritic or senile plaques) and tangled bundles of fibers (neurofibrially tangles) in the brain. The neuritic plaque is a cluster of degenerating axonal and dendritic nerve terminals that contain amyloid-beta protein. Neurofibrially tangles are seen in the cytoplasm of abnormal neurons in those areas of the brain (hippocampus, cerebral cortex) most affected by Alzheimer's disease.
If there a clear pattern of inheritance within a family is established, then the person is said to have "familial Alzheimer's disease". If there is no inheritance it's known as "sporadic Alzheimer's disease."
Alzheimer's Disease is named after Alois Alzheimer, a German physician who in 1906 described changes in the brain tissue of a 51-year old woman who had dies of an unusual mental illness.