In addition, Rotimi notes, the HapMap enables researchers to tackle questions about gene/environment interactions for the first time. "You now have people coming from different parts of the world, and you have the opportunity to study different environmental factors," along with the individuals' genetic variations, he says.

Tom Hudson, who has been engaged in the HapMap from its inception as former assistant director of the Whitehead Institute/MIT Center for Genome Research, agrees. Now director of the Montreal Genome Centre and Génome Québec Innovation Centre at McGill University, Hudson has launched one of several international studies that are applying HapMap data to human disease research.

The Montreal center is starting with a study of colon cancer that will examine the entire genomes of 1,200 people with and 1,200 without the disease, for genetic differences. The best leads from this phase will then be checked in 5,000 additional patients in the state of Washington, Newfoundland, Ontario, and France. "Many groups in disease areas are forming consortia, just like HapMap," says Hudson. "[We] need large numbers of families or individuals in these studies, usually more than any single group has."

Hudson has also undertaken more focused studies examining variations in 150 candidate genes for childhood asthma among 5,000 individuals and 200 genes in 15,000 heart attacks patients. The goal is to develop a deeper understanding of the links between genes and environment in the origins of these diseases. Another group at the Montreal Genome Centre has embarked on a whole genome study to find genes associated with type II diabetes.

Other research groups have started similar large studies: Donnelly is leading a U.K.-based consortium looking for genes related to a host of diseases: type I and type II diabetes, hypertension, cardiovascular disease, bipolar disorder, Crohn's disease, rheumatoid arthritis, and susceptibility to tuberculosis. Meanwhile, researchers in Japan plan to screen 300,000 people in a search for genes related to 47 different diseases.

David Altshuler, for one, expects the progress to be rapid. For the first time, he points out, researchers can look broadly across the genome, around the world for genes linked to the most common diseases. And while it will take years before diagnostic tests and treatments based on such studies reach patients, the results could transform public health worldwide. "I do think this is an inflection point," Altshuler says.