Leaps in gene scan science help decode diseases

DNA will be extracted, and early this summer, more than half a million spots on the microscopic strands from each mother and baby will be assessed for clues to where the genetic variations may lie.

The DNA will be analyzed at the Center for Inherited Disease Research at Johns Hopkins University in Baltimore. Robots will put a tiny drop of DNA-bearing solution from each person onto a clear glass slide roughly the size of a business card, with four drops per slide.

The lab’s DNA scanners, blue boxes each about twice as big as a desktop printer, will reveal what DNA “letter” appears in more than 580,000 spots in the genetic material, said lab director Kimberly Doheny.

This scan takes about half an hour per sample. Once the results are available, the scientists will use statistical tests to find the telltale signs of a possible gene affecting risk of premature birth. They’ll double-check to make sure any such signal shows up in more than one population.

Even five years ago, such a detailed examination of DNA from so many people would have been inconceivable.

Genome scans offer some major advantages over previous gene-hunting techniques. Scientists don’t have to start by guessing what genes might be involved in a disease, or confine themselves to families where a tendency to an illness is inherited.

And the genome-scan approach reveals genes with only subtle influence on the risk of getting sick, too slight to be found by earlier methods. That’s just the kind of gene that plays a role in common illnesses like heart disease.

Even if its impact on risk is small, a newly found gene can be a bonanza to scientists if it reveals something new about the biology of a disease. That in turn can give hints for finding new treatments.

Customized tests
For non-scientists, the most direct payoff of finding new disease genes may be in devising tests to identify people at elevated risk for a particular disorder.

Most genetic variants found in the genome scans boost a person’s risk by around 50 percent. If the disease risk is fairly low, that’s “not something you’d lose much sleep over,” Watson said.

More useful, he said, is the notion of finding variants in maybe a half-dozen genes that affect the risk for a disease, then testing a person for all of them at once to come up with a more powerful indicator.

Earlier this year, for example, Swedish researchers reported preliminary evidence that men with four or five particular gene variants ran more than four times the risk of getting prostate cancer than men with none of them. When family history was factored in, such a combined test could identify men who ran a nine-fold higher risk.

An Iceland-based company, deCode Genetics, announced in February that it is offering a test for eight genetic variants related to prostate cancer. Altogether, the variants make 10 percent of men run twice the normal risk of prostate cancer, and 1 percent run three times the normal risk, the company said.

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Dr. Teri Manolio of the National Human Genome Research Institute said it’ll take more work to figure out the value of genetic testing for prostate cancer. There is no proven treatment to prevent it; the only advice to a man at higher risk would probably be for more aggressive screening for the disease.

Then there’s the question about what people will do with gene test results. What if you already know that everybody should watch their weight, for example, and then a DNA test shows a heightened risk for diabetes and your doctor tells you to ... watch your weight?

Maybe people would pay more attention to health advice if they knew they were genetically vulnerable to getting sick otherwise. But maybe not. It’s an open question, Manolio said.

“I think some people will,” Watson said. “I think some people just won’t, because they’re the kind of people who aren’t influenced by those sorts of things.... I’m not pessimistic or optimistic, but I’m sure not everybody does the right thing.”

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