Most African-Americans have a mixed background with some European ancestry and therefore contain a mixture of African and European signposts at these locations. The goal was to figure out if people with high blood pressure were more likely to have the African or European version of these 270 differences. People in the study were participants in the U.S. National Heart, Lung and Blood Institute's Family Blood Pressure Program.

This strategy highlighted regions near two of the signposts, one on chromosome 6 and the other on chromosome 21. In both cases, African-Americans with high blood pressure were more likely to have the African version of the location. According to Risch, chances are that the people with high blood pressure also have the African version of a gene in that region that increases their chances of developing high blood pressure.

Risch said the very fact that this type of analysis could turn up regions of interest is exciting. "This will raise a big discussion about how well a genome-wide analysis that is based on ancestry will work when you are dealing with a complex disease," he said. Until this was completed, some people doubted that the intertwined risk factors of diet, exercise and genetics could be unraveled.

A large task still remains. In addition to finding the genetic culprit, there's still the problem of figuring out how that gene increases high blood pressure risk. Does it simply enhance problems caused by a bad diet, or would the gene alone cause hypertension even in a person who exercises regularly?

Even with these unresolved questions, Risch said the study is a first step towards an answer to why African-Americans are more prone to high blood pressure.

Hua Tang, PhD, a Stanford graduate student now at the Fred Hutchinson Cancer Research Institute, also participated in the study.

med.stanford/