Prostate cancer tends to run in families, so it's clear that genes play at least a part in triggering it. Exactly what genes, though, have been tough to identify. But a new report in the current Proceedings of the National Academy of Sciences trumpets the discovery, not of a gene quite yet, but of a region of DNA on chromosome 8 that evidently contains such a gene.

Researchers at Harvard Medical School already knew that African-American men tend to be 1.6 times more likely than Caucasian Americans to come down with prostate cancer. They also knew that African Americans tend to be racially mixed, having at least a small amount of non-African blood. And they assumed, reasonably enough, that it was the African part of their genetic  heritage that was causing the increased disease prevalence.

So the scientists searched the DNA of 1,597 African Americans who had prostate cancer, looking for regions with the highest concentration of purely African genes. It was here that they found a stretch most highly associated with prostate-cancer risk.

"This paper identifies a genetic risk factor that about doubles the likelihood of prostate cancer in younger African American men," says principal investigator David Reich, PhD, Harvard Medical School assistant professor of genetics with the HMS Department of Genetics and the Broad Institute. "This finding may explain why younger African Americans have an increased risk for prostate cancer than do other populations—and may also explain why this increased risk in African Americans attenuates with older age."

What it means: It's far too early to use this discovery for any sort of treatment, but it does offer a warning flag for men who have a genetic predisposition to be especially vigilant about being tested for incipient prostate cancer. This is even more true for younger African-American men, in whom the gene seems to confer the bulk of the extra risk.

From the Archive:

Mar. 16, 2006: Peppers and Prostates
Oct. 3, 2005: Weight Worries and Prostate