A new study shows how understanding the “shopping cart” of race and ethnicity may be crucial to finding the best way to treat patients.
By Nathan Collins
A digital representation of the human genome. (Photo: Mario Tama/Getty Images)
Although race remains a central issue in American politics, a growing number of scientists are abandoning race and ethnicity as social constructs, rather than hard biological facts. The alternative is genetic ancestry—that is, whether we got our genes from ancient Europeans, Africans, Asians, or some other group. Yet when it comes to treating disease, a new study suggests, genetic ancestry isn’t enough.
“Genetic ancestry isn’t the end-all be-all,” says senior author and University of California–San Francisco Professor Esteban Burchard. There’s a “shopping cart” of non-genetic factors including shared environment, diet, and even values that also affect health. The question is, how much does the shopping cart matter, and which items matter the most?
For Burchard and his collaborators, the desire to find answers runs deep. Burchard’s speciality, asthma, disproportionately affects African Americans and some Latino groups—about one in six Puerto Ricans have the disease, compared to only around one in 20 Mexican Americans.
“We went down the rabbit hole” trying to understand those results, Burchard says. But in addition to the results, there was an underlying question: What do race and ethnicity actually mean? (It can’t help that, even today, few studies focus on African Americans or Latinos, let alone their subgroups.)
Fortunately, the research team, which included Joshua Galanter and UCSF Assistant Professor Noah Zaitlen, had detailed information on 573 Latino kids from across the United States. That data, collected as part of a long-term asthma study, included socioeconomic status, tobacco exposure, and more—plus a host of genetic data. The researchers focused on methylation, one of the main chemical processes the body uses to deactivate specific genes and a contributor to a wide range of diseases, and how it varies between Mexican Americans, Puerto Ricans, and other Latino subgroups.
Overall, the researchers report in the journal eLife, genetic ancestry explained about 75 percent of the differences between participants—a lot, in other words, but “we’ve got 25 percent more to go,” Burchard says.
A closer look at the data revealed that, among roughly 450,000 genetic sites the team examined, there were 916 where methylation patterns were reliably connected to ethnicity—that is, where the researchers could do a decent job telling Mexican Americans and Puerto Ricans apart based on their DNA. That’s not entirely surprising, by the way, because of another finding: There’s a much higher proportion of Native American genetic ancestry in Mexican Americans compared to Puerto Ricans.
But genetic ancestry only goes so far—specifically, it only explains what’s going on at about two-thirds of the 916 sites. The rest—314 of them—couldn’t be connected to genetic ancestry. Intriguingly, many of those sites have previously been connected to environmental and social influences, such as smoking, air pollution, and stress.
In other words, both genetics and race matter for health.
That could ultimately prove pertinent at the doctor’s office, Zaitlen says. Doctors often screen for certain diseases—heart disease, for example—based on race categories such as non-white Hispanic, but “we know these categories are too coarse.” The latest results, Burchard and Zaitlen say, may pave the way for doctors to provide more personalized and effective care to their patients.