Alzheimer's disease

n. A form of senile dementia characterized by progressive brain deterioration and the formation of neurological plaques and neurofibrillary tangles in the brain. It is a common form of senile dementia and can be diagnosed only after death by examination of brain tissue for plaques and neurofibrillary tangles. The first symptom is usually a reduction in the capacity to detect odors which often is unnoticed as there are many causes of reduced ability to smell. It is characterized by progressive loss of cognitive abilities and memory, and death results when brain impairment progresses to the state where physiological capacities are affected such as ability to swallow or perform other bodily maintenance activities. It is usually first detected in persons over age 65, and its incidence increases rapidly after that age. Accurate rates of occurrence are difficult to determine as postmortem examination of the brain is seldom done in elderly persons who die with dementia, and so it is easily confused with other forms of dementia such as multi-infarct dementia. It has been correlated with the presence of the ApoE4 allele on chromosome 19, but that is not a sole cause of the disorder.