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.