A couple of new studies confirm what many of us have feared: each of us is surprisingly unique genetically. This is to be feared because of the impact it will have on the future of personalized medicine. Our individual uniqueness will make predicting our risk for disease much trickier than we thought. And it will make finding treatments that much harder too.
You’ve probably read that all humans share somewhere between 99.5% and 99.9% of their DNA. Usually this is translated into saying that we have a difference in our DNA every 1000 bases or so. (By bases I mean the A’s, G’s, C’s, and T’s that make up our DNA.)
These differences were supposed to be shared by many people. So a lot of people would have a G at a certain position and the rest of us would have a T. The first study shows that this is not the case.
Instead, we all have many rare DNA differences scattered throughout our DNA. When the researchers looked at 202 different genes from 14,002 people, they found a rare variant every 17 bases or so. This is way higher than many people thought.
What’s worse is that these differences aren’t all benign. The other study published in Science showed that a surprisingly high percentage, around 2.3%, is predicted to significantly impact a gene. In other words, we are all burdened with many gene-altering and so potentially harmful DNA differences.
So the world of genetics is getting turned on its head yet again. Not so long ago, the idea was that diseases shared a common set of DNA differences. So everyone with sickle cell anemia had a certain DNA difference (or at least a certain few). Same thing with cystic fibrosis and all the other genetic diseases.
Now it looks like there are many individual paths to a disease. For example, while most cases of cystic fibrosis do involve glitches in the CFTR gene, there are lots of glitches that can cause the disease. And that makes figuring out your chances for getting or passing cystic fibrosis to your children even harder.
Many (perhaps even most) of us will have DNA differences in our CFTR genes that haven’t been seen before. We don’t yet know which differences can lead to cystic fibrosis.
Believe it or not, cystic fibrosis is the easy case; at least it usually involves just one gene. More complex genetic diseases like Type 2 diabetes or Alzheimer’s are going to be complicated by the fact that many different genes can be involved and we are all littered with unique differences in these genes.
For example, there will be a huge set of genes involved in Type 2 diabetes. Each of us will have numerous unique DNA differences strewn throughout these genes. Some of these changes will increase your risk for getting Type 2 diabetes and some will lower your risk.
Unfortunately the way scientists can tell if a difference is involved in a disease is by comparing two large groups of people with and without the disease. If a certain DNA difference turns up more often in the disease group, then it may be involved in causing the disease.
But now everyone has lots of unique DNA differences, many of which can contribute to disease. The people in the disease group won’t share a lot of the same differences that lead to disease. This means it is going to be hard to figure out which differences matter.
Our best bet may be to figure out as much DNA from as many people as possible so we can at least start to get a handle on which genes are involved in a particular disease. Then we can start to explore which DNA differences matter and which ones don’t. One thing is for sure, this is going to take awhile to sort out.
This came out after I wrote the blog. More evidence that knowing our DNA may not help us out as much as we had hoped.