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Alzheimer's genes: Are you at risk?

Several genes have been associated with Alzheimer's disease, but more research is needed.

By Mayo Clinic staff

Alzheimer's genes are genes that make you more likely to develop Alzheimer's disease. Genes control the function of every cell in your body. Some genes determine basic characteristics, such as the color of your eyes and hair. Other genes can make you more likely to develop certain diseases — including Alzheimer's.

Researchers have identified several Alzheimer's genes — genes that are associated with Alzheimer's disease. But genetic risk factors are just one part of the Alzheimer's story, a complex narrative that scientists continue to try to unravel.

Most common late-onset Alzheimer's gene

While some rare forms of Alzheimer's occur before the age of 65, the most common variety of Alzheimer's usually begins after the age of 65. The most common gene associated with this late-onset Alzheimer's is called apolipoprotein E (APOE).

APOE has three common forms:

  • APOE e2 — the least common — appears to reduce the risk of Alzheimer's.
  • APOE e4 — a little more common — appears to increase the risk of Alzheimer's.
  • APOE e3 — the most common — doesn't seem to affect the risk of Alzheimer's in either direction.

Genes aren't only factor
Because you inherit one APOE gene from your mother and another from your father, you have two copies of APOE gene — for example, one APOE e3 gene and one APOE e4 gene. Having at least one APOE e4 gene increases your risk of developing Alzheimer's. And if you have two APOE e4 genes, your risk is even higher.

But not everyone who has an APOE e4 gene — or even two APOE e4 genes — develops Alzheimer's. And the disease occurs in many people who have no APOE e4 gene. This indicates that the APOE e4 gene affects risk, but it is not a causative gene. Other genetic and environmental factors are likely involved in the development of Alzheimer's.

Other late-onset genes

As research on the genetics of Alzheimer's progresses, researchers are uncovering links between late-onset Alzheimer's and a number of other genes. Several examples include:

  • SORL1. Some variations of SORL1 appear to increase the production of amyloid-beta fragments, which form structures called amyloid plaques in the brain. These plaques are one of the hallmarks of Alzheimer's disease.
  • CLU. This gene helps regulate the clearance of amyloid-beta from the brain. The association of this gene with Alzheimer's reinforces the theory that an imbalance in the production and clearance of amyloid beta is central to the development of Alzheimer's.
  • CR1. A deficiency of the protein this gene produces may contribute to chronic inflammation in the brain. Inflammation is another potential contributing factor to the development of Alzheimer's.
  • PICALM. This gene is linked to the process by which brain nerve cells (neurons) communicate with each other. Smooth communication between neurons is important to the proper functioning of neurons and to the formation of memory.

Researchers hope that discovery of these genes will help them learn more about the basic mechanisms of Alzheimer's and consequently, ways to treat and prevent the disease. But similar to APOE, these genes are risk factors, not direct causes. In other words, having a variation of one of these genes may increase your risk of Alzheimer's. But knowing whether you have such a variation doesn't help predict whether you will ultimately develop Alzheimer's.

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References
  1. Alzheimer's disease genetics fact sheet. National Institute on Aging. http://www.nia.nih.gov/alzheimers/publications/geneticsfs.htm. Accessed May 19, 2010.
  2. Genetic conditions: Alzheimer disease. Genetics Home Reference. http://ghr.nlm.nih.gov/condition/alzheimer-disease. Accessed May 19, 2010.
  3. Genes: APOE. Genetics Home Reference. http://ghr.nlm.nih.gov/gene/APOE. http://ghr.nlm.nih.gov/gene/APOE. Accessed May 19, 2010.
  4. Ertekin-Taner N. Genetics of Alzheimer's disease: A centennial review. Neurological Clinics. 2007;25:611.
  5. Meng Y, et al. Association between SORL1 and Alzheimer's disease in a genome-wide study. Neuroreport. 2007;18:1761.
  6. Sleegers K, et al. The pursuit of susceptibility genes for Alzheimer's disease: Progress and prospects. Trends in Genetics. 2010;26:84.
  7. Harold D, et al. Genome-wide association study identifies variants at CLU and PICALM associated with Alzheimer's disease. Nature Genetics. 2009;41:1088.
  8. Lambert JC, et al. Genome-wide association study identifies variants at CLU and CR1 associated with Alzheimer's disease. Nature Genetics. 2009;41:1094.
  9. Genetic testing. Alzheimer's Association. http://www.alz.org/national/documents/topicsheet_genetictesting.pdf. Accessed May 28, 2010.
  10. Genetic Information Nondiscrimination Act of 2008: Fact sheet. National Human Genome Research Institute. http://www.genome.gov/10002328. Accessed May 28, 2010.
AZ00047 Aug. 5, 2010

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