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Alzheimer's disease is a neurodegenerative disorder characterized by loss of memory along with other cognitive changes, including aphasia (language impairment), apraxia (difficulty carrying out motor activities despite intact motor function), and agnosia (difficulty recognizing or identifying objects despite intact sensory function). There is a significant impairment in social and occupational functioning, as well as a behavioral disturbance commonly occurring in the disorder that may include apathy, loss of interest in daily activities, delusions, hallucinations, preservation, disinhibition, and depression. The cognitive, functional, and behavioral components have different manifestations at different stages of the disease, and the course of the disease is characterized by gradual onset and continuing cognitive decline.
The functional change is generally hierarchical, beginning with changes in instrumental activities of daily living (using the telephone, shopping, food preparation, housekeeping, accessing transportation, taking medications, handling finances) and later affecting the basic activities of daily living (toiletting, feeding, dressing, grooming, physical ambulation, and bathing). The onset of the disorder is insidious, and the disease progresses over ten to twenty years. In the early stages the individual may require supervision or assistance for activities such as managing finances and shopping. In the later stages, 24-hour help may be required. Social skills are often preserved until the later stages, and individuals may be very impaired or be at significant risk before the disease is recognized.
The cause of Alzheimer's disease is not understood completely. Age is the biggest risk factor, but other risk factors may be involved, including a low level of education and significant head injury. A family history of the disease also increases the risk. With familial Alzheimer's the inheritance is autosomal dominant, and chromosomes 1, 14, 19, and 21 have been identified as important in the inheritance. It appears that individuals with the gene apolipoprotein E4 have an increased risk, while the genes apoE2 and apoE3 may have a protective function. ApoE status, however, is not considered a part of predictive testing and apoE4 is not considered a cause of the disease. The genetics of Alzheimer's disease suggest a heterogeneous disorder, and several other genes are being investigated.
Alzheimer's disease is the most common type of dementia in older people. Prevalence estimates of dementia in Canada suggest that 8 percent of all Canadians age 65 and over have some type of dementia. Of these, 5.1 percent have Alzheimer's disease. In the larger population, rate for Alzheimer's disease was 1 percent in the 65 to 74 age group and 26 percent in those over 85 years. For all types of dementia the rates were 2.4 percent and 34.5 percent respectively. These rates are comparable to those found in incidence studies conducted in New York.
Author Info: B. LYNN BEATTIE, The Gale Group Inc., Macmillan Reference USA, New York, Gale Encyclopedia of Public Health, 2002
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