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

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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 disease.

Researchers have identified several genes that are associated with Alzheimer's disease. However, genetic risk factors are just one part of the Alzheimer's disease story.

Most common late-onset Alzheimer's gene

Although a rare form of Alzheimer's disease occurs before age 65 (early-onset Alzheimer's disease), the most common variety of Alzheimer's disease usually begins after age 65 (late-onset Alzheimer's disease). The most common gene associated with late-onset Alzheimer's disease 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.

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

Not everyone who has one or two APOE e4 genes develops Alzheimer's disease. The disease occurs in many people who have no APOE e4 gene, suggesting that the APOE e4 gene affects risk but is not a cause. Other genetic and environmental factors likely are involved in the development of Alzheimer's disease.

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 on chromosome 11 appear to be associated with Alzheimer's disease.
  • CLU. This gene helps regulate the clearance of amyloid-beta from the brain. Research supports the theory that an imbalance in the production and clearance of amyloid-beta is central to the development of Alzheimer's disease.
  • CR1. A deficiency of the protein this gene produces may contribute to chronic inflammation in the brain. Inflammation is another possible factor in the development of Alzheimer's disease.
  • PICALM. This gene is linked to the process by which brain nerve cells (neurons) communicate with each other. Smooth communication between neurons is important for proper neuron function and memory formation.
  • TREM2. This recently identified gene is involved in the regulation of the brain's response to inflammation. Rare variants in this gene are associated with an increased risk of Alzheimer's disease.

Researchers seek to learn more about the basic mechanisms of Alzheimer's disease and, consequently, ways to treat and prevent the disease.

As with 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. However, knowing whether you have such a variation doesn't help predict whether you'll develop Alzheimer's.

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References
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  2. Alzheimer disease. Genetics Home Reference. http://ghr.nlm.nih.gov/condition/alzheimer-disease. Accessed Nov. 15, 2012.
  3. APOE. Genetics Home Reference. http://ghr.nlm.nih.gov/gene/APOE. Accessed Nov. 15, 2012.
  4. Alonso Vilatela ME, et al. Genetics of Alzheimer's disease. Archives of Medical Research. In press. Accessed Nov. 29, 2012.
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  6. Genetic testing. Alzheimer's Association. http://www.alz.org/alzheimers_disease_steps_to_diagnosis.asp. Accessed Nov. 29, 2012.
  7. Genetic information nondiscrimination act of 2008: Fact sheet. National Human Genome Research Institute. http://www.genome.gov/10002328. Accessed Nov. 29, 2012.
  8. Diagnosis of Alzheimer's disease and dementia. Alzheimer's Association. http://www.alz.org/alzheimers_disease_diagnosis.asp. Accessed Nov. 29, 2012.
  9. About Alzheimer's disease: Diagnosis. National Institute on Aging. http://www.nia.nih.gov/alzheimers/topics/diagnosis. Accessed Nov. 29, 2012.
  10. Sleegers K, et al. The pursuit of susceptibility genes for Alzheimer's disease: Progress and prospects. Trends in Genetics. 2010;26:84.
  11. Meng Y, et al. Association between SORL1 and Alzheimer's disease in a genome-wide study. Neuroreport. 2007;18:1761.
  12. Williamson J, et al. Genetic aspects of Alzheimer disease. Neurologist. 2009;15:80.
  13. Boeve BF (expert opinion). Mayo Clinic, Rochester, Minn. Dec. 4, 2012.
  14. NINDS Alzheimer's disease information page. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/alzheimersdisease/alzheimersdisease.htm. Accessed Dec. 5, 2012.
  15. Jonsson T, et al. Variant of TREM2 associated with the risk of Alzheimer's disease. The New England Journal of Medicine. In press. Accessed Dec. 5, 2012.
AZ00047 Feb. 9, 2013

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