DNA Diving for Alzheimer’s

My 23andMe test tells me I am less likely to end up with the brain on the left. Image courtesy of Klunkwe.

I was having lunch with a colleague the other day and we got to talking about genetic testing (yes, we are that geeky). I told him about how my 23andMe test had missed my being prediabetic. This says a lot about what 23andMe’s test can tell me about my risk for diabetes. Not much.

Now as I have said before, the fact that 23andMe can’t tell me that I’m likely to become diabetic from their DNA test isn’t their fault (other than, perhaps, some overselling on their part). Diabetes research just isn’t far enough along to be able to accurately predict whether someone will get diabetes or not. Or to make any really meaningful prediction about diabetes at all.

We then got to talking about Alzheimer’s. Turns out his family tree is littered with Alzheimer’s on both his mother’s and father’s side. He ran into a similar problem–23andMe doesn’t report anything for Alzheimer’s.

But here the situation is a bit different than for diabetes. There are a couple of DNA markers that can tell us a lot about our future risk for late onset Alzheimer’s. It just so happens that 23andMe doesn’t report on them.

These markers deal with the APOE gene. This gene comes in three common versions: e2, e3, and e4. People with two copies of the e4 version are 15 times more likely to develop Alzheimer’s and if they do end up with the disease, it tends to come earlier. (One copy of e4 increases your risk about 3 times.)

With a little help from my colleague, I decided to dig a bit deeper into Alzheimer’s and see what I could figure out from what 23andMe did provide. Turns out I can figure out a whole lot about my APOE status. And that I can help other people figure out more from their results too.

The two markers (also called SNPs) that deal with APOE and Alzheimer’s are rs429358 and rs7412. Here, according to SNPedia, are the combinations of these markers that tell you your APOE status:

To my surprise, 23andMe gives information on one of them, rs7412. Even though this isn’t usually enough to tell whether you have the dreaded e4 version or not, in my case it was. I almost certainly do not have any versions of e4 (yay!).

See, my results at rs7412 are TT*. If I am interpreting these results correctly, this means I almost certainly have two copies of the e2 version of the APOE gene. In terms of my Alzheimer’s risk this is great news as being e2/e2 actually lowers your risk for getting the disease. (There is a chance I could be e1 but this doesn’t seem to be a very common version at all.)

Of course this doesn’t mean I won’t get Alzheimer’s…I still might. After all, the risk for someone over 85 getting Alzheimer’s is almost 50%. Even though this number lumps e4 and e2 folks together, e2 people do not have a 0% risk for Alzheimer’s nor do e4 people have a 100% chance. People with e4 are just more likely to have Alzheimer’s than e2 people.

It might help to think about getting Alzheimer’s like drawing an inside straight in poker. Everyone might do it but people who are playing with wildcards are more likely to get it. These are the e4 folks. But it isn’t a for sure thing…you still may not draw the straight even with deuces wild.

Same thing with not having e4. Now I am less likely to draw that inside straight because there are no wild cards but it can still happen.

Because I was TT at rs7412, my case was pretty easy to figure out. Next blog I’ll try to help people out who are TC or CC at rs7412.

*Remember, we have two copies of each of our genes. So I have a T at rs7412 in one copy and a T at rs7412 in my other copy.

A video showing why knowing your APOE status isn’t necessarily a good thing.

Learn more about current Bay Area genetic research from KQED’s Forum.

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