Ask An Expert: Genetic Test for Alzheimer's

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Ask An Expert: Genetic Test for Alzheimer's

Question:

My father was recently diagnosed with Alzheimer's disease. I have heard of a "gene test" that people can take to see if they will contract this disease. Is this available? What do you suggest that I do? This disease also "runs" on my mother's side of the family.

Answer:

Alzheimer's disease (AD) is a common cause of age-related dementia, but not all dementia is due to Alzheimer's. Scientists have known for many years that AD runs in families. The familial form of AD comes in two flavors: early-onset and late-onset. People with early-onset familial AD show symptoms before age 65, as early as their 40s or 50s. Genetic testing is available for early-onset AD, but only about 2 percent of familial AD is the early-onset type. It appears that your family has late-onset AD, where symptoms appear after age 65 (if this is not true, then there may be testing available for your family). Unfortunately, scientists don't know as much about the genes that cause late-onset AD.

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 AD. But using the 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 ready for prime-time."

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.

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Last updated:	January 24, 2007

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