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Dementia is a brain disorder that seriously affects a person's
ability to carry out daily activities. Alzheimer's disease
is the most common form of dementia among older people. It
involves the parts of the brain that control thought, memory,
and language. Every day scientists learn more, but right
now the causes of Alzheimer's disease are still unknown,
and there is no cure.
Scientists think that up to 4.5 million people in the United States suffer from Alzheimer's disease. The disease usually begins after age 65 and risk goes up with age. While younger people also may get Alzheimer's disease, it is much less common.
About 5 percent of men and women ages 65 to 74 have Alzheimer's disease, and nearly half of those age 85 and older may have the disease. It is important to note, however, that Alzheimer's disease is not a normal part of aging.
Alzheimer's
disease is named after Dr. Alois Alzheimer, a German doctor.
In 1906, Dr. Alzheimer noticed changes in the brain tissue
of a woman who had died of an unusual mental illness. He
found abnormal clumps and tangled bundles of fibers. The
clumps are now called amyloid plaques and the tangles are
called neurofibrillary tangles. Today, these plaques and
tangles in the brain are considered hallmarks of Alzheimer's
disease.
Scientists
also have found other brain changes in people with Alzheimer's
disease. There is a loss of nerve cells in areas of the brain
that are vital to memory and other mental abilities. There
also are lower levels of chemicals in the brain that carry
complex messages back and forth between nerve cells.
Alzheimer's
disease may disrupt normal thinking and memory by blocking
these messages between nerve cells.
Causes and Risk Factors
Scientists
do not yet fully understand what causes Alzheimer's disease.
There probably is not one single cause, but several factors
that affect each person differently. Age is the most important
known risk factor for Alzheimer's disease. The number of
people with the disease doubles every 5 years beyond age
65.
Family history
is another risk factor. Scientists believe that genetics
may play a role in many Alzheimer's disease cases. For example,
familial Alzheimer's disease, a rare form of Alzheimer's
disease that occurs between the ages of 30 and 60, can be
inherited.
The more common form of Alzheimer's disease is known as late-onset. It occurs later in life, and no obvious family pattern is seen in most cases. One risk factor for this type of Alzheimer's disease is a gene that makes one form of a protein called apolipoprotein E, or apoE.
Everyone has apoE, which helps carry cholesterol in the blood. Only about 15 percent of people have the form that increases the risk of Alzheimer's. It is likely that other genes may also increase the risk of Alzheimer's or protect against it, but they remain to be discovered.
Scientists still need to learn a lot more about causes and risk factors. In addition to genetics and apoE, they are studying education, diet, environment, and molecular changes in the brain to learn what role they might play in the development of this disease.
To read more of this excellent article from NIH Senior Health,
please click here: http://nihseniorhealth.gov/alzheimersdisease/defined/01.html
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