Causes of Alzheimer's Disease

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, early-onset familial Alzheimer's Disease, a rare form of Alzheimer's Disease that usually occurs between the ages of 30 and 60, is inherited. The more common form of Alzheimer's Disease is known as late-onset. It occurs later in life, and no obvious inheritance pattern is seen in most families. However, several risk factor genes may interact with each other and with non-genetic factors to cause the disease. The only risk factor gene identified so far for late-onset Alzheimer's Disease is a gene that makes one form of a protein called apolipoprotein E (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 Disease. It is likely that other genes also may increase the risk of Alzheimer's Disease or protect against Alzheimer's Disease, but they remain to be discovered.

More information:
The NIA-sponsored Alzheimer's Disease Genetics Study seeks to learn more about risk factor genes for late onset Alzheimer's Disease.

Scientists still need to learn a lot more about what causes Alzheimer's Disease. In addition to genetics and ApoE, they are studying education, diet, and environment to learn what role they might play in the development of this disease. Scientists are finding increasing evidence that some of the risk factors for heart disease and stroke, such as high blood pressure, high cholesterol, and low levels of the vitamin folate, may also increase the risk of Alzheimer's Disease. Evidence for physical, mental, and social activities as protective factors against Alzheimer's Disease is also increasing.