Know Thyself

When you check a box on a form to indicate your race or ethnicity, you may be more in touch with your genetic makeup than you realize. A new study indicates that, at least for most major groups in the United States, self-identified ethnicity corresponds closely with what genetic markers reveal, suggesting that race can be a useful guide to at least some aspects of biology.

No one denies that some groups are more vulnerable than others to certain disorders, such as sickle-cell anemia, and thus knowing someone's race or ethnicity can be as pertinent to diagnosis as knowing their sex. But observers differ over whether race is purely a cultural indicator or whether it signifies underlying biological variability that is relevant to many conditions in addition to single-gene disorders such as sickle cell anemia.

In the new study, a team led by Neil Risch now at the University of California, San Francisco, profiled 3636 people living in 15 locations in the U.S., who were participating in a study on the genetics of hypertension. The subjects identified themselves either as non-Hispanic white, African American, Hispanic, or East Asian (Chinese or Japanese). The researchers then statistically plotted the genetic distances between the groups based on 326 genomic markers--stretches of DNA with no known functional significance--that are known to vary among people whose ancestors came from different parts of the world.

The white, black, and Asian groups fell into distinct clusters, with the lone Hispanic group (Chicanos in Starr County, Texas) hovering closest to the Caucasian cluster. An analysis of the Asians alone put them in two sub-clusters, Chinese and Japanese. None of the other genetic groups could be subdivided, suggesting that there isn't enough genetic difference to distinguish people from northern versus southern Europe, for example.

"The correspondence between genetic cluster and [self-reported ethnicity] is remarkably high," the authors report in this month's issue of the American Journal of Human Genetics. Indeed, genetic information clashed with self-reported race in only five (0.14%) of the 3636 subjects. Risch points out that racial self-identification is a lot cheaper than genetic tests, and the fact that it correlates highly with genetic differences suggests it can be useful in guiding treatment decisions.

Some experts, such as physician Richard Cooper of Loyola University in Chicago, say such research casts no light on medically relevant racial differences because the DNA markers, while differing between ethnic groups, are not directly linked with diseases. However, others such as David Goldstein of University College London point out that "group membership" can offer clues about the probability of having a particular disorder. People who identify as African American, for example, are as a group at higher risk for disorders that do have a genetic component, such as hypertension and diabetes.

Related site
Neil Risch's Stanford page