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http://www.webmd.com/cancer/news/20080102/down-syndrome-may-curb-cancer?src=rss_public

Down Syndrome May Curb Cancer
Gene May Make Cancer Rarer in People With Down Syndrome
By Miranda Hitti
WebMD Medical NewsReviewed by Louise Chang, MDJan. 2, 2008 -- New research shows that the genetic roots of Down syndrome may protect against cancer.

The finding may lead to the creation of new cancer drugs, researcher Roger H. Reeves, PhD, a professor at Johns Hopkins University School of Medicine, tells WebMD.

Such drugs are a long way off, but "people with Down syndrome have now given us all the possibility of lowering the incidence of cancer in everybody," says Reeves.

That possibility lies in the DNA of Down syndrome, Reeves' team reports in tomorrow's edition of Nature.

People with Down syndrome have three copies of chromosome 21. People without Down syndrome have two copies of that chromosome. Some past studies have shown that cancer is rarer in people with Down syndrome, but not all studies have reached that conclusion.

To learn more about the link between cancer and Down syndrome, Reeve and colleagues studied mice with genes that make them likely to develop intestinal cancer. Some of the mice also had a third chromosome that gave them a condition similar to Down syndrome.

The mice with the extra chromosome were less likely to develop intestinal cancer and had smaller tumors than the other mice.

A gene called Ets2 -may get the credit for that pattern. That gene sits on chromosome 21, so Down syndrome provides an extra copy of the Ets2 gene -- and that abundance may repress cancer, Reeves notes.

He points out that the Ets2 gene had been suspected of causing -- not curbing -- cancer. But in Down syndrome, the extra copy of that gene may tip the balance in favor of cancer prevention.

"This is a new kind of gene which, if you overexpress it, represses tumor formation," says Reeves.

"If there were no such thing as Down syndrome, we probably wouldn't have found this because it wouldn't make a lot of sense to take these oncogenes that we thought were genes that cause cancer and try to express them at high levels to try to prevent cancer. But that's what happens" in their experiment, says Reeves.

He cautions that further studies are needed to see if that's true of other cancers, apart from the intestinal cancer his team studied in mice.

Reeves says he and his colleagues want to develop a potential drug that would boost Ets2 in people without Down syndrome to curb cancer.

It will take more work to see if that can be done safely, but the study "offers an explanation for why having three, rather than the normal two, copies of chromosome 21, the hallmark of Down syndrome in humans, provides some protection from solid tumors," writes David Threadgill, PhD, in an editorial published with the study.

Threadgill is an associate professor of genetics at the University of North Carolina at Chapel Hill.