23andMe's DNA testing was always fun. Now it is more useful as well.

As anyone who follows this blog knows, I had my DNA tested awhile back by a company called 23andMe.  I wrote about what I learned and didn’t learn from their testing in a bunch of blog entries.

In my mind 23andMe has always been a sort of recreational genetics testing company.  You can find out about your earwax, whether you are likely to have blue eyes or be lactose intolerant and lots of other minor sorts of traits.  This is stuff you probably already know but for geeks it is pretty cool to see them written out in their DNA.

The company always offered some health data too but it wasn’t that strong.  For example, they could tell you if you carried the most common DNA difference that could lead to cystic fibrosis (CF) but not about the less common ones.  In fact, I gave them an incomplete for their carrier testing a few months back.

Since then, the company has gone away from being a place where you get your DNA tested for coolness’ sake to one with a focus on health and/or ancestry.  With this change has come a much-improved product for people interested in what their DNA tells them about their carrier status for a variety of genetic diseases.

Carrier status is important if you are considering having a child.  If you and your partner both carry the broken versions of a gene that could lead to a disease, then your child would be at an increased risk for getting that disease.  For example, if both you and your partner have a nonworking copy of the CFTR gene, then, depending on the exact DNA you each have, your child could have up to a 25% chance of ending up with CF.

This is why the first iteration of 23andMe carrier testing wasn’t as useful as I would have liked.  They tested only one of the 100’s of different DNA variants in the CFTR gene that can lead to CF. Since this DNA variant only accounts for about half the cases of CF, there was a good chance that something would get missed.  This is no longer true.

As part of the refocusing, 23andMe looks for 31 different variants in the CFTR gene that are known to cause CF. Now this isn’t hundreds but is more than the 23 recommended by the American College of Medical Genetics.  And in fact 23andMe includes these 23 in the 31 it tests.

Of course the testing still isn’t perfect but no testing is.  Some of the tests are only useful for certain ethnic groups.  And there is no upfront genetic counseling to help you decide whether or not genetic testing would be useful in your situation anyway.

But the bottom line is that 23andMe’s testing for genetic diseases that you might be carrying is much stronger than it was before.  So much so that it can even give you some piece of mind for many of these diseases.

In some ways I’ll miss the more whimsical look at DNA that 23andMe used to represent.  But this obviously wasn’t a good business model for anyone except those enamored of DNA.  And 23andMe does need to make a profit…

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What can genetic testing tell you?

A while back I took a 23andMe genetic test that looks at over 600,000 different spots on my DNA. The last few blogs I have been going over my genetic test results with an eye on how useful they are. And how well the results are explained.

Last blog I wrote about how current genetic tests aren’t that great at predicting your risk for common, complicated diseases like diabetes or Alzheimer’s. This time I thought I’d focus on what today’s genetic tests can be very good at and whether or not 23andMe does a good job with these.

Current genetic tests are very good at predicting your risk for rare, simple genetic diseases like cystic fibrosis (CF) or Huntington’s disease (HD). And at predicting the chances that your kids will get these diseases too.

Genetic tests for these diseases work because most of them are caused by a single gene gone awry. Testing for a single gene is relatively easy.

For example, most cases of CF happen because of known differences in the CFTR gene. A genetic test can look for these differences and tell you if you and/or your spouse have any of them. If you both do, they can also give you a pretty good idea about the chances that your kids will get them too.

Of course, we don’t know all of the differences in the CFTR gene that can cause CF. And some differences only cause CF some of the time. And there are people with everyday, run-of-the-mill CFTR genes who get CF because of differences in different genes.

Still, as genetic tests go, these are pretty good. If a test comes up with a known CFTR difference that causes CF, then you have a pretty good idea of what your chances for developing CF are. If your spouse gets tested too, then your kids’ chances can be determined as well.

So how does 23andMe do? OK, I guess…

First off, they look at eight of these sorts of diseases under a category called Carrier Status. The diseases they look at are shown in this image:

For me, the first big result is that I am a carrier for a variant that can lead to hemochromatosis. This isn’t surprising since 1 in 8-12 people of Northern European descent in the U.S. are too, but it is definitely something to watch out for. It may be important for my wife to be checked too so we can make sure none of our kids got two copies. (Luckily hemochromatosis is easily treated by giving blood on a regular basis.)

Some of the other results are less illuminating. For example, I do not carry the CF difference they test for (delta F508). This is of course great news. Unfortunately, this variant only accounts for about half of the CF cases out there. Which means I could be a carrier for CF, just not a carrier of the most common variant that they happen to test for.

The same thing goes for most if not all of the other carrier status diseases (sickle cell anemia is an exception). Some like BRCA (breast cancer) are as poorly covered as CF while others like Bloom’s disease cover a larger percentage of cases.

23andMe is pretty upfront about the limitations of their testing once you dig a bit into the results. But still, if they’re going to look at 600,000 different parts of my DNA, you’d think they could add a few more to give me a stronger answer about whether or not I am a CF carrier.

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