Scientists think that about 4 to 6 million Americans currently suffer from AD. The disease usually begins after age 60, and risk goes up with age. While younger people also may get AD, it is much less common. About 3 percent of men and women ages 65 to 74 have AD, and nearly half of those age 85 and older may have the disease. It is important to note, however, that AD is not a normal part of aging.
 

AD 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 (now called amyloid plaques) and tangled bundles of fibers (now called neurofibrillary tangles). Today, these plaques and tangles in the brain are considered hallmarks of AD.
Scientists also have found other brain changes in people with AD. 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 messages back and forth between nerve cells. AD interferes with normal thinking and memory.Scientists do not yet fully understand what causes AD. There probably is not one single cause, but several factors that affect each person differently. Age is the most important known risk factor for AD. The number of people with the disease doubles every 5 years beyond age 65.
 

Family history an important risk factor. Scientists believe that genetics may play a role in many cases of AD. For example, familial AD, a rare form of AD that usually occurs between the ages of 30 and 60, can be inherited. However, in the more common form of AD, which occurs later in life, no obvious family pattern is seen. One risk factor for this type of AD is a protein called apolipoprotein E (apoE). Everyone has apoE, which helps carry cholesterol in the blood. The apoE gene has three forms. One seems to protect a person from AD, and another seems to make a person more likely to develop the disease. Other genes that increase the risk of AD or that protect against AD probably remain to be discovered.
Scientists still need to learn a lot more about what causes AD. In addition to genetics and apoE, they are studying education, diet, environment, and other medical conditions to learn what role they might play in the development of this disease.
 

AD begins slowly. At first, the only symptom may be mild forgetfulness. People with AD may have trouble remembering recent events, activities, or the names of familiar people or things. Simple math problems may become hard to solve. Such difficulties may be a bother, but usually they are not serious enough to cause alarm. However, as the disease goes on, symptoms are more easily noticed and become serious enough to cause people with AD or their family members to seek medical help. For example, people in the later stages of AD may forget how to do simple things such as brushing their teeth or combing their hair. They can no longer think clearly. They begin to have problems speaking, understanding, reading, or writing. Later on, people with AD may become anxious or aggressive, or wander away from home. Eventually, they need total care.

For more information about Alzheimer's disease and related disorders, visit the ADEAR Center site.

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