Published On Apr 18, 2017
A New Genomics of Race
Gene changes related to culture may play into how disease affects the body, according to researcher Esteban Burchard.
Physicians generally try not to think of race or ethnicity when treating a patient. But too much sensitivity may be leaving stones unturned, says Esteban Burchard, a professor of medicine and pharmacy at the University of California, San Francisco.
The incidence of asthma, for instance, has strong ethnic correlations. So Burchard set out to collect genetic material from thousands of children with and without asthma, as well as information about their racial identity and medical and social histories. With the cooperation of 14 institutions across the United States, he hopes to tease out what respective roles genes and environments might play in the problem.
Along this path, Burchard is exploring the complex ways that race and ethnicity are manifested in DNA. It has long been known that some genes correlate strongly with where someone’s ancestors came from. Genes that cause sickle cell anemia, for example, are much more common in people who trace their heritage to central Africa.
But Burchard’s most recent paper shows that ethnicity—the culture someone participates in today—may also create a distinct layer of genetic information that affects a person’s health.
Q: What prompted you to look at race and genetics?
A: Minorities are understudied in all U.S.-funded biomedical research. About 95% of the research for lung disease in the past 20 years has been conducted only in populations of European origin. We’re making a lot of assumptions that all racial groups have the same genetic risk factors. That’s just not the case. Getting a better understanding of the real variations can help treatments across the board. And that can move the moral compass of science toward more justice.
Q: What are your studies looking for?
A: The prevalence of severe asthma significantly varies among different racial and ethnic groups. Compare it to all other common diseases—obesity, heart disease, diabetes—and asthma shows the highest disparity of this kind. In the United States, asthma death rates are highest in Puerto Ricans and African Americans, intermediate in whites, and lowest in Mexican Americans.
Notice that at both the high and low asthma-prevalence and mortality extremes, you have two distinct Latino/Hispanic ethnic groups: Puerto Ricans and Mexicans. I’ve been fascinated by this disparity since I was a young trainee, and I started the GALA studies (gene-environment studies of asthma in Latino/Hispanic children) to understand it better. I wanted to know what part of this difference is environmental or social, what part is genetic and what part is something else—a sort of combination of the two.
Q: What do you mean by a combination?
A: Your DNA is made up of genes that control the function of your body. You can think of the genes as light switches that are flipped on or off. Those are the genes you receive from your ancestors, plus or minus a few mutations along the way. But there is another factor, called methylation, which acts like a dimmer switch. It can either increase or decrease the activity of genes.
Methylation can be caused by environmental factors. And those methylation patterns can be inherited. Researchers have carried out studies of Holocaust survivors and shown that their trauma changed the methylation patterns on their DNA—and that those changes were inherited by their offspring.
So in our last paper, we were looking to see whether ethnicity—living in a Mexican community versus a Puerto Rican one, for instance—carries distinct methylation patterns.
Q: How did the paper explore this topic?
A: In a racially mixed group of children, 220 of whom self-identified as Puerto Rican and 276 of whom self-identified as Mexican American, we looked for distinct methylation patterns.
We found that about 75% of the variation of methylation was explained by the different ancestries of the two groups—tied to older genetic patterns, in other words. But the other 25% was explained by social factors such as diet and lifestyle, which are tied to ethnicity.
Q: What are the clinical implications of this work? Can it improve asthma treatment or prevention?
A: This goes back to my original observation: One Hispanic ethnic group has a really high prevalence of asthma, and another ethnic group has a really low prevalence, but the world had lumped them all together as “Latino” or “Hispanic.” There are gene-level differences between the two groups, if we can only understand their implications. We know already that there are drugs for which the response to the medication varies by race and ethnicity. One of these is albuterol, one of the most commonly prescribed asthma drugs in the world. Puerto Rican patients have lower responsiveness to it than Mexican patients.
It’s too early for direct applications. But it should serve as a wake-up call. We need to better understand all of the factors—biological, environmental, and social—that mean significant variation in how people experience disease and treatment.
Q: By tracing race and ethnicity to the genome, do you worry that you’re opening the door to your work being misunderstood by racists?
A: This has already happened to me. We published a 2003 paper in The New England Journal of Medicine showing the clinical benefits of using race and ethnicity as an epidemiology tool. A former leader of the Ku Klux Klan used our research to say, “Well, since blacks have sickle cell disease, and Jews have Tay-Sachs disease, blacks must also have genes that are associated with aggressive behavior, and Jews must have genes associated with money hoarding.”
Race is clearly a loaded topic in every arena, especially medicine. But I don’t think we should bury our heads just because some bad people will misuse our data. We have to stay focused on our desired outcomes.