Question: If I or a close family member has Alzheimer's disease, should I have my children or other family members tested for the ApoE4 gene?
Answer: The ApoE4 gene increases risk for Alzheimer's disease but it does not guarantee it. And it probably has to work together with other genetic factors that we're still trying to identify, as well as environmental factors. So, the recommendation today is to not use ApoE4 as a genetic predictor for Alzheimer's disease, and it would not be recommended that children of Alzheimer's parents have an ApoE4 test to assess their risk. Why? Because it's not yet reliable.
However, with that said, in a patient who's already diagnosed with dementia, most probably Alzheimer's disease, the ApoE4 test could be used to increase the probability that this is indeed dementia due to Alzheimer's disease.
In other words, it can be used as what we call a differential diagnostic.