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It was six years ago that scientists completed a milestone in biology - the complete genetic sequence of a human being. They hope the accomplishment would lead to a better understanding of the genetics of diseases. And lately, that's exactly what's been happening.

Last month, there was news about obesity. Last week, it was diabetes and today, as NPR's Joe Palca reports, it's heart disease.

JOE PALCA: Some diseases are caused when a single gene goes bad. Scientists have been reasonably successful finding the genes for those kinds of diseases. But researchers believe most common illnesses involve many genes, and finding those genes has been tricky.

Now, scientists are using a new way of searching those genes. They do a genome-wide search - looking at all the DNA in the genomes of people with the disease, and all the DNA in the genomes of people without a disease, and they find places where there are differences.

That's what Ruth McPherson and her colleagues at the Ottawa Heart Institute in Canada did for people with heart disease.

Dr. RUTH McPHERSON (Cardiologist and Director, Lipid Clinic, Lipid Research Laboratory, Ottawa Heart Institute): The reason for doing a study like this is to find generic variance that will identify high-risk people so we can treat them, but secondly, to develop new knowledge that may lead to a better understanding of biological pathways that lead to heart attacks.

PALCA: 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 is taking about is that these genome-wide searches frequently tell scientists about genetic regions they never suspected were associated with diseases.

Noticed I said genetic regions, not genes. There's a good reason for making the distinction, based on what McPherson and her colleagues found on chromosome 9.

Dr. McPHERSON: This is not within a gene that was known to be related to heart disease. In fact, it is a region between genes.

Dr. DAVID ALTSHULER (Department of Molecular Biology and Diabetes Unit, Massachusetts General Hospital): It would have been called junk DNA, and yet, it's not junk DNA.

PALCA: That's David Altshuler of Massachusetts General Hospital in Boston. Right now, Altshuler says, 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.

One funny thing, if Altshuler's comments sound a bit familiar it's because he made those comments last week on this program. Then he was talking about a similar kind of study. Here's the rest of Altshuler's comments from last week.

Dr. ALTSHULER: One of the most interesting finding is a region on the ninth chromosome where there's a clear relationship between inheriting a different sequence here and diabetes.

PALCA: Yes. He just said diabetes, not heart disease. It turns out the same region of chromosome 9 is now implicated in both major diseases. What does that mean? Good question, no answers yet.

And Altshuler makes one more important point, there have already been lots of studies - and there'll be lots more - that find these genetic regions related to common diseases.

Dr. ALTSHULER: And I actually think this is going to be an important challenge for medicine - is to figure out how do we use these new genetic risk factors in a responsible way. Because there's a big difference between something being valid - which these risk factors are; which means they do truly have an influence on risk - and their being useful, which would mean that measuring them actually helps the patient.

PALCA: For now, Altshuler says, these genetic risk factors are primarily useful to scientists trying to unravel the genetic mechanisms that underlie common diseases.

Joe Palca, NPR News, Washington.

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