Understanding Alzheimer's Disease

by National Institute on Aging

Alzheimer's Disease Defined

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 million Americans suffer from Alzheimer's disease. The disease usually begins after age 60, and risk goes up with age. While younger people also may get Alzheimer's disease, it is much less common.

About 3 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.

Portrait of Dr. Alois Alzheimer. 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.

Quiz

1. Alzheimer's disease is the most common form of dementia among older people.

TRUE is the correct answer. Although there are other forms of dementia associated with aging, Alzheimer's disease is the most common form.

2. Alzheimer's disease is a normal part of aging.

FALSE is the correct answer. Although Alzheimer's disease usually begins after 60 and is more common among older people, it is not a normal part of aging.

3. When researchers examine the brains of people who have died of Alzheimer's, they find nothing unusual.

FALSE is the correct answer. The brain tissue of people who have died from Alzheimer's disease contains abnormal clumps called amyloid plaques and bundles of fibers called neurofibrillary tangles. These plaques and tangles are considered the hallmarks of Alzheimer's disease.

4. Scientists believe that about 40 million people in the United States suffer from Alzheimer's.

FALSE is the correct answer. It is estimated that approximately 4 million people in the United States suffer from Alzheimer's disease.

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. However, in the more common form of Alzheimer's disease, which occurs later in life, no obvious family pattern is seen. One risk factor for this type of Alzheimer's disease is a protein called apolipoprotein E, or apoE.

Everyone has apoE, which helps carry cholesterol in the blood. The apoE gene has three forms. One form seems to protect a person from Alzheimer's disease, and another form seems to make a person more likely to develop the disease. Other genes that increase the risk of Alzheimer's disease or that protect against Alzheimer's disease probably 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 viruses to learn what role they might play in the development of this disease.

Quiz

1. Scientists

A. will never know what causes Alzheimer's.
B. can pinpoint the exact cause of Alzheimer's.
C. do not know for sure what causes Alzheimer's.

C is the correct answer. Scientists do not yet fully understand what causes Alzheimer's disease. However, it is clear that Alzheimer's disease develops as a result of a complex series of events that take place inside the brain over time which causes nerve cells in the brain to die. Ongoing research yields more valuable information each year about the causes of this disease.

2. The most important known risk factor for Alzheimer's disease is

A. age.
B. depression.
C. family history of the disease.

A is the correct answer. Age is the most important known risk factor for Alzheimer's disease. The disease usually begins after 60 and the risk goes up with age.

3. Alzheimer's disease occurs most frequently among people

A. 85 and older.
B. 65 to 75 years of age.
C. 60 to 65 years of age.

A is the correct answer. About 3 percent of men and women ages 65 to 74 have the disease, but nearly half of those age 85 and older may have the disease. The average age at diagnosis is about 80.

4. Another risk factor for Alzheimer's disease is

A. depression.
B. being overweight.
C. family history of the disease.

C is the correct answer. Family history is another risk factor for Alzheimer's disease. Scientists believe that genetics may play a role in many Alzheimer's disease causes. For example, familial Alzheimer's disease, a rare form of the disease that occurs between the ages of 30 and 60, can be inherited. However, in the more common form of Alzheimer's disease, which occurs later in life, no obvious family pattern is seen. There is no evidence that either depression or being overweight are risk factors for Alzheimer's.

About the Author

www.nia.nih.gov
NIA, one of the 27 Institutes and Centers of NIH, leads a broad scientific effort to understand the nature of aging and to extend the healthy, active years of life. In 1974, Congress granted authority to form NIA to provide leadership in aging research, training, health information dissemination, and other programs relevant to aging and older people.