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Introduction

Alzheimer’s disease has no known single cause, but in the last 15 years scientists have learned a great deal about factors that may play a role.

Biology of Alzheimer’s disease

Scientists believe that whatever triggers Alzheimer’s disease begins to damage the brain years before symptoms appear. When symptoms emerge, nerve cells that process, store and retrieve information have already begun to degenerate and die. Scientists regard two abnormal microscopic structures called "plaques" and "tangles" as Alzheimer hallmarks. Amyloid plaques (AM-uh-loyd plaks) are clumps of protein that accumulate outside the brain’s nerve cells. Tangles are twisted strands of another protein that form inside cells. Scientists do not yet know whether plaques or tangles cause Alzheimer’s or are a byproduct of some other process. Clinical trials of experimental drugs targeting amyloid are under way and should help clarify the role plaques play.

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Risk Factors

Late-onset Alzheimer’s, which chiefly affects individuals over age 65, is the more common form of the illness that is most often associated with the term "Alzheimer’s disease." The greatest known risk factors for late-onset Alzheimer’s are increasing age and a family history of the disease. The likelihood of developing late-onset Alzheimer’s approximately doubles every five years after age 65. By age 85, the risk reaches nearly 50 percent. Scientists have so far discovered one gene that increases risk for late-onset disease.

Rare, familial types of Alzheimer’s found in a few hundred families worldwide have been linked to specific genes. Individuals who inherit these genes are virtually certain to develop the disease, usually before age 65, and sometimes as early as their 30s or 40s.

Researchers worldwide are working to discover other factors that affect Alzheimer risk. Some of the most exciting emerging evidence suggests that strategies for general healthy aging may also help reduce the risk of developing Alzheimer’s. These measures include controlling blood pressure, weight and cholesterol levels; exercising both body and mind; and staying socially active.

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Related resources

See Causes and Risk Factors in the Topic Index.

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