Alzheimers Home > Genetics and Age as Alzheimer's Risk Factors
Some risk factors can affect the chances that a person will develop a disease or condition. Alzheimer risk factors that we cannot control include age and genetics.
Age is the most important known risk factor for Alzheimer's disease. The risk of developing the condition doubles every 5 years over age 65. Several studies estimate that around half the people over age 85 have Alzheimer's disease. These facts are significant because of the growing number of people who are 65 years of age and older -- more than 34 million Americans to date. Even more significant, the group with the highest risk of Alzheimer's disease -- those older than 85 -- is the fastest growing older population group in the country.
Genetics is the other known risk factor for Alzheimer's disease that a person can't control. Scientists have found genetic links to the two forms of Alzheimer's disease. Early-onset Alzheimer's disease is a very rare form of the condition that can occur in people between the ages of 30 and 60. In the 1980s, researchers found that mutations (or changes) in certain genes on three chromosomes cause early-onset Alzheimer's disease. A person has a 50-50 chance of developing early-onset Alzheimer's disease if one parent has any of these genetic mutations.
Late-onset Alzheimer's disease, the more common form, develops after age 65. In 1992, researchers found that certain forms of the apolipoprotein E (APOE) gene can influence the risk of Alzheimer's disease:
- APOE e2, a rarely occurring form, may provide some protection
- APOE e3, the most common form, appears to play a neutral role
- APOE e4, which is found in about 40 percent of people with AD, appears to increase the risk.
Researchers are now intensively searching for other genes that may be linked to late-onset Alzheimer's disease. Discovering these risk-factor genes is essential for understanding the causes of Alzheimer's disease and pinpointing targets for drug development and other prevention or treatment strategies.