A family history of Alzheimer’s is not necessary for an individual to develop the disease. However, research shows that those who have a parent or sibling with Alzheimer's are more likely to develop the disease than those who do not have a first-degree relative with the Alzheimer’s. Those who have more than one first-degree relative with Alzheimer’s are at an even higher risk. When diseases tend to run in families, either heredity (genetics), environmental factors – or both – may play a role.

Genetics and Alzheimer’s

There are two categories of genes that influence whether a person develops a disease: (1) risk genes and (2) deterministic genes. Researchers have identified Alzheimer's genes in both categories.

  • Risk genes increase the likelihood of developing a disease, but do not guarantee it will happen. Researchers have found several genes that increase the risk of Alzheimer's. APOE-e4 is the first risk gene identified, and remains the gene with strongest impact on risk. APOE-e4 is one of three common forms of the APOE gene; the others are APOE-e2 and APOE-e3.

    We all inherit a copy of some form of APOE from each parent. Those who inherit one copy of APOE-e4 have an increased risk of developing Alzheimer's. Those who inherit two copies have an even higher risk, but not a certainty. In addition to raising risk, APOE-e4 may tend to make symptoms appear at a younger age than usual.

Genetic testing

Genetic tests are available for both APOE-e4 and the rare genes that directly cause Alzheimer’s. However, health professionals do not currently recommend routine genetic testing for Alzheimer’s disease. Testing for APOE-e4 is sometimes included as a part of research studies.

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  • Deterministic genes directly cause a disease, guaranteeing that anyone who inherits one will develop a disorder. Scientists have found rare genes that cause Alzheimer's in only a few hundred extended families worldwide. These genes, which are estimated to account for less than 1 percent of Alzheimer's cases, cause familial early-onset forms in which symptoms usually develop between a person's early 40s and mid-50s.

    Although the genes that cause "familial Alzheimer's" are rare, their discovery has provided important clues that help our understanding of Alzheimer's. All of these genes affect processing or production of beta-amyloid, the protein fragment that is the main component of plaques. Beta-amyloid is a prime suspect in decline and death of brain cells. Several drugs now in development target beta-amyloid as a potential strategy to stop Alzheimer's disease or significantly slow its progression.

    Two international investigations are under way to gain further insight into Alzheimer's disease by studying individuals with deterministic Alzheimer's genes: (1) The Dominantly Inherited Alzheimer Network (DIAN), funded by the National Institute on Aging (NIA), includes 10 flagship research centers in the United States, the United Kingdom and Australia. (2) The Alzheimer's Prevention Initiative (API) focuses on an extended family in Antioquia, Colombia, in South America. At 5,000 members, this is the world's largest family in which a gene that causes Alzheimer's has been identified. API collaborators include DIAN. Learn more on our Treatment Horizon page.

Genetic tests are available for both APOE-e4 and the rare genes that directly cause Alzheimer's. However, health professionals do not currently recommend routine genetic testing for Alzheimer's disease. Testing for APOE-e4 is sometimes included as a part of research studies.

About at-home genetic tests

The Alzheimer’s Association® suggests that you talk to a genetic counselor before deciding to take an at-home test and, if you decide to get genetic testing for Alzheimer’s, again after you receive the results. The National Society of Genetic Counselors website provides a searchable directory to locate a counselor. With an unsupervised, at-home test, there is a real possibility of misunderstanding results, which could result in making misinformed decisions about your health. If you are already experiencing symptoms of cognitive decline, see a healthcare professional for a full evaluation.
 

A closer look at genes linked to Alzheimer’s

The 23 human chromosome pairs contain all of the 30,000 genes that code the biological blueprint for a human being. This interactive illustration highlights the chromosomes containing each of the three genes that cause familial Alzheimer's and the gene with the greatest impact on Alzheimer's risk.

23 chromosome pairs

23 Chromosome Pairs; 4 Alzheimer's Genes Identified:

Amyloid precursor protein (APP),
discovered in 1987, is the first gene with mutations found to cause an inherited form of Alzheimer's.

Presenilin-1 (PS-1),
identified in 1992, is the second gene with mutations found to cause inherited Alzheimer's. Variations in this gene are the most common cause of inherited Alzheimer's.

Presenilin-2 (PS-2),
discovered 1993, is the third gene with mutations found to cause inherited Alzheimer's.

Apolipoprotein E-e4 (APOE4),
discovered in 1993, is the first gene variation found to increase risk of Alzheimer's and remains the risk gene with the greatest known impact. Having this mutation, however, does not mean that a person will develop the disease.

Amyloid precursor protein (APP), discovered in 1987, is the first gene with mutations found to cause an inherited form of Alzheimer's.

Presenilin-1 (PS-1), identified in 1992, is the second gene with mutations found to cause inherited Alzheimer's. Variations in this gene are the most common cause of inherited Alzheimer's.

Presenilin-2 (PS-2), discovered 1993, is the third gene with mutations found to cause inherited Alzheimer's.

Apolipoprotein E-e4 (APOE4), discovered in 1993, is the first gene variation found to increase risk of Alzheimer's and remains the risk gene with the greatest known impact. Having this mutation, however, does not mean that a person will develop the disease.