Diagnosing Alzheimer's: Genetic Tests

Reviewed by: HU Medical Review Board | Last reviewed: June 2019 | Last updated: October 2019

Diagnosing Alzheimer’s disease involves a variety of tests and exams to help rule out illnesses and determine the underlying causes of the presenting symptoms. A definitive diagnosis of Alzheimer’s is only able to be done on autopsy, so it’s helpful to use all possible screening and assessment tools to ensure that the diagnosis is as accurate as possible.1 This can include taking medical and symptom history and doing a physical exam, various neurological exams, and imaging scans. While genetic testing is used in certain cases, genetic testing is generally not recommended for the typical late-onset Alzheimer’s patient.2

What is genetic testing?

Genetic testing is testing that can identify changes or mutations in genes, chromosomes, or proteins.3 It can also identify changes in DNA, called polymorphisms, that have increased association with a particular disease. This kind of testing can help physicians rule out hereditary diseases, as well as confirm them – and in the case of family members, can help predict the risk of developing or passing on a genetic disorder.3 Although genetic testing can provide information previously unknown, it has risks as well as benefits. There are at-home genetic testing kits, but it is highly recommended that individuals discuss genetic testing with both their physicians and a genetic counselor. There are risks and benefits to the testing, and the results can have a significant impact on an individual – which is why any results should be reviewed with a genetic counselor in order to avoid misunderstanding or misinterpretation and to go over what the results actually mean in practical terms for an individual and their future. For example, an individual may have a mutation in a gene that's associated with Alzheimer’s disease, but the risk of developing Alzheimer’s disease is still low. Genetic counselors are highly trained in understanding the data associated with gene changes and can help explain risks.

Genetic testing and Alzheimer’s disease

Most people who develop Alzheimer’s disease have late-onset Alzheimer’s, which develops in the mid-to-late 60s. While no specific gene has been found to directly cause late-onset Alzheimer’s disease, a genetic risk factor has been found: having one form of the apolipoprotein E (APOE) gene on chromosome 19.4 There are three possible forms of APOE: APOE2, APOE3, or APOE4. Everyone has two copies of the APOE gene but can have different combinations of the different forms such as APOE2/APOE3, APOE3/APOE4, etc. If an individual has two copies of APOE4, the risk for developing late-onset Alzheimer’s disease is increased. This increases a person’s risk of developing Alzheimer’s disease. Generally, genetic testing is not done for late-onset Alzheimer’s patients, although sometimes it is done in research settings.

Early-onset Alzheimer’s disease occurs between 30 and 60 years old, and there is thought to be a genetic component to it, particularly for those who have early-onset familial Alzheimer’s disease (FAD). Early-onset FAD is caused by any one of several single-gene mutations on chromosomes 21, 14, or 1.4 These are mutations in genes called APP (amyloid precursor protein), PS1 (presenilin 1) or PS2 (presenilin 2). Many individuals whose family members have had genetic testing participate in clinical studies that look at brain changes in families with various mutations for Alzheimer’s disease. If an individual is showing symptoms of early-onset Alzheimer’s disease, genetic testing may be helpful.

Should you get genetic testing?

Routine genetic testing is not done for Alzheimer’s disease, mainly because there are no treatments to prevent, slow, or cure the disease, and so the test results would have no impact on choosing treatment and would not affect the course of the disease. However, an individual may make modifications in lifestyle that can reduce the risk of developing the disease, such as changes in exercise, nutrition, and social activity. An individual may be also able to participate in a clinical trial that investigates if certain treatments may be more beneficial for individuals with certain gene mutations. That being said, routine genetic testing is generally not recommended or done. If an individual still wants to pursue genetic testing for Alzheimer’s disease, it’s best for them to talk with their doctor honestly about what they want to get out of the test, the potential impact it might have on them and their family, and what they expect to do with the information. A genetic counselor is highly recommended to go over the results with the patient and explain how the findings affect the patient’s health and future health or medical decisions.

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