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Friday, October 9, 2015
Alzheimer's Disease and Genetics
My father (age 60 now) was diagnosed with Primary Progressive Aphasia at the age of 55. He now also has Frontal Temporal Dementia and exhibits almost everything described in Picks disease. What is the best way to determine if this is EOFAD or if this occurred as a result of the Aphasia. Do my 3 other siblings and I(ranging in age from 30 - 40) need to be aware that we may have a mutated gene?
Thank you very much for your inquiry. I can give you a couple of general points in response to your question, but more specific information about your particular situation can only be gained by obtaining care from clinicians (like neurologists and genetic counselors) who are or can become familiar with your father's and extended family's medical history.
Unfortunately, it is expected that someone with a diagnosis of Primary Progressive Aphasia would progress to frontotemporal dementia. Therefore, it is likely that symptoms related to frontotemporal dementia and Pick's disease can be explained by the initial diagnosis of Primary Progressive Aphasia.
There is one gene that has been identified and can be tested for that causes frontotemporal Dementia and several that can cause Early Onset Familial Alzheimer disease (EOFAD). However, testing for these genes does not identify mutations in all cases, even when there is a strong family history of the disease. Therefore, we know that there must be more genes that can cause these diseases that we haven't discovered yet.
There can be many causes of both frontotemporal dementia and Alzheimer disease, only some of which are genes that can be tested for. The information below is what is available in the literature and may not apply to you and your family. The only way to learn more about what might be going in your family would be to seek out care from a neurologist or genetics professional who can study your family more carefully.
Having said that, there is a gene, called MAPT, that has been shown to cause frontotemporal dementia. Genetic testing for this gene is generally conducted on the person who has the condition when that person also has other relatives who have had the same thing. Generally, mutations of the MAPT gene are found between 25%-40% of the time in such cases. If such a mutation is identified, then relatives of the patient, like siblings or children, can be tested for that mutation. Children have a 50% chance of having inherited that mutation from their parent..
There have been three different genes shown to cause EOFAD. These are called APP, PSEN1, and PSEN2. Again, the usual course of action is to test a patient who has a family history of early onset dementia (average age of onset in the family < 65 years). In this kind of scenario, genetic testing of the APP gene can identify mutations in 10%-15% of people with EOFAD, testing of the PSEN1 gene can find mutations in 30%-70% of people with EOFAD, and testing of the PSEN2 gene can detect mutations in less than 5% of people with EOFAD. Again, children would have a 50% chance of having inherited the mutation from their parent.
Melissa Butson, ScM, CGC
Formerly, Clinical Adjunct Instructor of Neurology
School of Medicine
Case Western Reserve University