Genetic Testing for Alzheimer's Disease

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Genetic Testing for Alzheimer's Disease

Question:

If I have gene testing, can I find out if I might be a carrier of Alzheimer's? One grandparent on each side of my family was diagnosed with it and both eventually died from Alzheimer's.

Answer:

Alzheimer's disease is a common cause of age-related dementia, but not all dementia is due to Alzheimer's. Among all cases of Alzheimer's, only a minority are the inherited form, which can either be early-onset (symptoms before age 65) or late-onset.

Genetic testing is available for early-onset Alzheimer's, but only about 2% of familial Alzheimer's is the early-onset type. Early-onset of familial Alzheimer's has a dominant inheritance pattern. This means that a person only needs to inherit one copy of the changed gene to get the disease. If one of your parents had a change in one of these genes, you have a 50% chance of having the same change, and each of your children has a 50% chance of inheriting it from you.

It sounds like your family may not have early-onset Alzheimer's. (You did not mention any problems for your parents.) Even with a family history, most cases are late-onset Alzheimer's, where symptoms appear after age 65. Scientists don't know as much about the genes that cause late-onset Alzheimer's.

You may have heard about a test for a gene called APOE. Certain changes in the APOE gene are more common among people with late-onset Alzheimer's. We'll call these the "high-risk" APOE changes. If a person already has dementia, the physician may use an APOE test to help decide if the dementia is more likely related to Alzheimer's.

But using the APOE test to predict if a healthy person will get Alzheimer's is NOT reliable. Some people with "high-risk" APOE changes don't get Alzheimer's, while others get Alzheimer's even though they don't have "high-risk" APOE changes.

Imagine receiving a test result saying you will get Alzheimer's and then you worry and worry but never get the disease! For this reason, genetic testing to predict if you will develop late-onset Alzheimer's is not advisable. You should talk to your doctor about what makes sense based on your family history.

David T. Miller, M.D., Ph.D. is a clinical geneticist at Children's Hospital, Boston and an Instructor at Harvard Medical School. He is also Assistant Director of the DNA Diagnostic Laboratory at Children's Hospital.

Last updated:	July 20, 2009