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If you're new to this blog and want some context for it, read this post from the day I announced my Alzheimer's disease and this post about the day I announced I had lost it. For more info, visit my website with my autobiography and all blog entries in chronological order for easier reading to catch up. There's also a sermon on the spiritual lessons I've learned through this journey through my damaged mind.

Friday, September 27, 2013

Should You Have Genetic Testing?

Washington DC


As part of a research study, I was recently tested for the Apolipoprotein E (ApoE) gene, which is linked to the development of Alzheimer’s.  There are at least three different forms of ApoE, one that seems to protect somewhat against the development of Alzheimer’s, another that seems neutral, and another (the ε4 variant) that increases the chances of developing Alzheimer’s.  I had one copy of ApoE-ε4, that is, I received one ApoE-ε4 gene from one parent and the other parent gave me one of the others.  Having one copy of ApoE-ε4 about doubles the chances of developing the usual (old-age) Alzheimer’s; if both copies are present, your chances of developing Alzheimer’s are 10 to 30 times higher than a person with no copies.

Should you get genetic testing for Alzheimer’s?  A factsheet  from the Alzheimer’s Association (from which much of this post is taken) recommends against routine testing except for research purposes and for a particular, rare kind of Alzheimer’s.

More than one hundred different genes are suspected of making you more susceptible to Alzheimer’s, although only a few have been clearly linked.  But genetics is only one cause of the disease.  Even an identical twin (exactly the same genes) of a person with Alzheimer’s has only a 25% chance of getting the disease.

Of all the genes, the ApoE-ε4 is the most prominent, but having it does not mean you have or will develop the disease; it only means that your chances are higher than average. Even two copies ApoE-ε4 just increase your chances.  Many who have the gene will never get Alzheimer’s; many who don’t have the gene will.  Outside a research context, the presence or absence of the gene changes nothing; it’s medically useless.

There are three rare genes that are different.  If you have one of those genes, you will definitely develop Alzheimer’s, and, since the genes are “autosomal dominant,” half your children will get the gene and thus the disease, too.  The onset of this kind of Alzheimer’s can be very young, even in the late twenties or thirties.  In these rare cases, however, the family will be well aware of its tragic history, and testing for the gene earlier in life can be very important in making life decisions, like whether or not to have children.

In the vast majority of cases, however, testing settles nothing.  If you just want to know, go ahead and get tested, but be aware that the best you’ll get is a false sense of security or an unjustified sense of dread. If you do choose to be tested, you should have careful pre- and post-test counseling so that you don’t misinterpret the results.

A potential problem in knowing your genetic status is that the results may be used (legally or illegally) to discriminate in providing insurance (for, say, long-term care) or in hiring.  People who choose to get tested, therefore, should find a way of doing so anonymously.

The cause of Alzheimer’s is at present unknown.  There are a number of risk factors, the most important of which is age.  The impact of other risk factors, including genetics, is relatively small in comparison.  Except in those rare families with autosomal dominant disease, there is no test that will predict who will or will not develop Alzheimer’s.

7 comments:

  1. i agree and dont agree

    for me personally i wanted to know my status
    since i have mild cognitive impairment amnestic type
    and am earlier in the disease than you are

    i want to know as much as i can so i can know as
    sure as a person can be that they have alzheimers disease

    i have the double apoe4 gene and know my chances are
    increased by 10-30 times that ill get alzheimers disease
    and with my symptoms that makes that probability higher

    add to that the fact that i have abnormal tau protein and abnormal
    beta amyloid levels in the spinal fluid
    and
    both parents died with the disease and a younger brother who just died with it
    and
    when my amyvid pet scan is done and if its positive

    then when its all added up
    as this is the best you can do today
    all this data as a physician i would tell my patient
    im afraid you probably have alzheimers disease and you should plan
    your life accordingly

    i personally take aricept every day and l do all those things you need to do to be healthy and like you am in research studies
    and soon plan to enter a treatment study

    so i agree and dont agree

    dewayne nash md


    ReplyDelete
    Replies
    1. I think my point still stands. You have plenty of reasons to believe that you have AD: you have
      1) MCI amnestic type
      2) abnormal tau and amyloid protein in your spinal fluid
      3) a positive PET amyvid (if it is positive), and
      4) a powerful family history
      It's seems to me that that provides a pretty strong case for a diagnosis of AD. While I, too, like to have as much information as I can, does the ApoE-ε4 information give you any new information?
      I'm not really arguing against it; as part of the research study, I found about mine, and it satisfies my curiosity. But I'm quite sure I wouldn't get the test if I had to pay for it myself.

      Delete
  2. i also want to add that you have an excellent blog
    as our diagnosis is similar you seem to put into words what i feel much better than i can
    thank you for blogging
    dewayne nash md

    ReplyDelete
  3. Great info to have. Thank you.

    ReplyDelete
  4. I once did a DNA test for a research study about chronic illnesses and what steps we take to improve out chances of not getting these illnesses. Such as diabetes, AD, cancers, etc. I got my DNA results and let it sit on my desktop for three days. I didn't want to open it, because I feared what could be in there. Finally, I realized that I could stare at it for years, and I would be as nervous as I was at that moment, so I opened it up. I don't have any genes for AD, so my risk is the same as the average population. I have two recessive genes for colon cancer, which I knew about, as my Mom was the fifth generation with colon cancer, so I get scopes regularly. I also had two recessive genes for galactosemia, I lack a enzyme to use milk correctly, babies die of it, older family members die of cirrhosis, even tho they do not drink. it was always a wonder why we had so many SIDS babies, dying at about 19 days after birth. Now we know.

    I was, of course, worried about the things we know about, Huntington's Chorea, AD, diabetes, and cancers. Its a weird feeling, getting a DNA result back. Its like opening up a mystery novel, except its your life in the plot.

    ReplyDelete
  5. I do not want to know. I've lost three of four grandparents to the disease and one parent. I am living my life to the fullest, expecting the best and preparing for the worst. Thanks for sharing this.

    ReplyDelete
    Replies
    1. Probably the most important factor in making this decision is knowing oneself and what is right for you. My best wishes for you.

      Delete

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