Question: What should a practicing physician know about using genetic testing for Alzheimer's?
Answer: A practicing physician should know that for the most common form of Alzheimer's disease, that strikes late in life, after 60 years old, we do not yet have a reliable genetic test. The one risk factor we know about -- ApoE4 -- can only be used after a patient is already diagnosed with dementia as a differential diagnostic to increase the odds that, yes, this is dementia due to Alzheimer's disease. And even then, a positive ApoE4 test would not confirm that it must be Alzheimer's disease.
In contrast, in the rare early-onset forms of Alzheimer's disease that strike under 60, which often have familial clustering, reliable genetic testing is available. Three different genes, 200 different mutations can be tested, which we know cause early-onset familial Alzheimer's disease, and there, genetic testing can be offered as an option.