Scientists are reporting that a region on chromosome 9 is related to an increased risk of heart disease. It's the latest finding in what has become a deluge of genetic information from studies that look for genetic differences between people who have a disease and those who don't. And, as in many cases, although scientists know the differences are biologically related to the disease, they don't know how.
Some diseases are caused when a single gene goes bad, and scientists have been reasonably successful at finding the genes for those kinds of diseases. But researchers believe most common illnesses involve many genes, and finding those genes has been tricky – until scientists started using genome-wide searches.
In the genome-wide search, scientists look at the DNA in the genomes of people who have the disease, and at the DNA in the genomes of people who don't have the disease, and they find places where there are differences.
That's what Dr. Ruth McPherson and her colleagues at the University of Ottawa Heart Institute in Canada did for people with heart disease.
"The reason for doing a study like this is to identify high-risk people so we can treat them, but secondly, [we want] to develop new knowledge that may lead to a better understanding of the biological pathways that lead to heart attacks," McPherson said.
As they report in the journal Science, the study found a region on chromosome 9 that made a small but measurable difference in someone's risk of heart attack.
The new knowledge McPherson mentioned is the fact that the genome-wide searches frequently alert scientists to genetic regions that they never suspected were associated with diseases.
And that's "genetic regions," not genes. There's a good reason for making the distinction, based on what McPherson and her colleagues found on chromosome 9.
"This is not within a gene known to be related to heart disease," she said. "In fact, it's in a region between genes."
That would have been called junk DNA, said David Altshuler of Massachusetts General Hospital in Boston. "And yet, it's not junk DNA."
Right now, Altshuler said, scientists have no idea how that chunk of DNA on chromosome 9 affects someone's risk of heart disease – all they know is that it does.
Altshuler told NPR last week about a similar kind of study: "One of the most interesting findings is a region on the ninth chromosome where there's a clear relationship between inheriting a different sequence here, and diabetes," he said.
That's diabetes, not heart disease. It turns out that the same region of chromosome 9 is now implicated in both diseases.
What does that mean? It's a good question, but there are no answers yet.
Altshuler pointed out that there have been a lot of studies, and there'll be a lot more, that find these genetic regions related to common diseases. And he said it's going to be a challenge for the medical community to figure out how to use the genetic risk factors in a responsible way.
"There's a big difference between something being valid – which these risk factors are; they truly do have an influence on risk – and their being useful, which would mean measuring them actually helps the patient," he said.
For now, Altshuler says, the genetic risk factors are useful to scientists primarily for trying to unravel the genetic mechanisms that underlie common diseases.