And it is even cheaper than this if you want to focus on just your genes. 23andMe is offering that very service for less than 1,000 dollars. Your DNA is finally within your grasp!

This drop in price is great news for scientists. They can now get more DNA sequenced for less money. This is driving genetics forward at breakneck speed.

This will probably also be great news for patients. For example, in the near future cancer patients will get the DNA in their tumors sequenced so they get prescribed the right medicine. We aren’t there yet, but if costs keep dropping, we will be soon.

For casual consumers, though, affordable DNA sequencing is much less useful. In fact, it might even make a difficult situation worse.

Right now we can get the results of a million or so of our bits of DNA. Some of these SNPs are within genes and some are outside of genes.

These SNPs have been looked at in lots of experiments. This means we have at least some idea about how each relates to various diseases. The same won’t be true of the new data that will be made available to you.

There are going to be changes in your genes that scientists haven’t seen before. And in many cases they won’t be able to tell you whether a certain change matters or not. You will end up with a bunch of differences for which there is little or no information. If you’re a worrier, this is going to cause problems.

Let’s take an easy example, cystic fibrosis (CF). Most of the time CF is caused by one or more of a defined set of DNA differences in the CFTR gene. Genetic testing now looks for changes known to cause CF.

Unfortunately, CFTR is a gene with a lot of changes, many of which have no effect. What this means is that many of us will have differences in our CFTR gene that haven’t been seen before. Will they cause cystic fibrosis? For many differences, we won’t know for sure.

This information may ultimately be helpful for scientists if they find enough people with particular differences. But it may not be that helpful to you. In fact, if you’re a worrier, you may be unnecessarily concerned about your kids ending up with CF because of your unique version of the CFTR gene.

And this is the easy example. Other diseases happen when many different gene versions all work together in a certain way. Some combinations of these gene versions will lead to disease or increased risk of disease and some won’t. If you pile on enough genes, you suddenly have so many combinations that it becomes very difficult to make any really predictions with only a few people’s DNA.

Right now I think it is safe to say that with genetics, we have lots of data but little understanding. To increase our understanding of human genetics, everyone should probably throw their DNA into the ring for scientists to study. The question is when do you want to know the results of what scientists are finding. At an early stage when everything is muddled or at a more defined, later stage.

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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