Why you should care
Your unique ancestral DNA could one day impact how doctors interpret your blood pressure or mammogram results.
Ancestral DNA testing could do more than reveal the identities of distant cousins or whether you descended from Genghis Khan.
Doctors could one day be using your unique ancestral history to diagnose and treat you better. So says a recent study published in Science, in which researchers from Stanford University, UC San Francisco and several other institutions investigated variations in Mexican ancestry. Some indigenous groups in Mexico are as genetically different as Europeans are from Chinese, making mestizos — most Mexicans — who have indigenous, European and African blood, wildly diverse. And those differences between individuals could impact the way doctors interpret even the most seemingly straightforward data.
We’re moving beyond blanket definitions like Mexican or Latino. … Now we’re putting finer details on that map.
The new findings suggest that physicians could sequence their patients’ DNA to precisely determine their genetic background and adjust clinical guidelines accordingly, versus the more common practice of factoring in race or ethnicity, as doctors do for kidney function tests, prostate cancer screenings and more. And in the U.S., doctors use only three categories: Mexican, African American or Caucasian, Burchard said. Not only could DNA sequencing prevent underdiagnoses, it would also save money and time otherwise spent on treating patients who may actually be healthy for someone with their genetic ancestry.
Racial categories like Asians and Latinos are largely based on physical features and culture — factors shaped by political, social and other reasons — not genetic differences. Populations even within a geographic region — like Mexico — show enormous genetic diversity.
An increasingly multiracial world might only worsen the problems of traditional race-based clinical guidelines. “How would you classify Obama?” asks Esteban González Burchard, a professor in the UCSF schools of Pharmacy and Medicine and study co-author. The president has a Kenyan father and white mother — so which race’s clinical guidelines would doctors use? Typically, a receptionist guesses patients’ race when they arrive for an appointment and relays that information to a technician, who then notifies the physician, Burchard said.
“We’re moving beyond blanket definitions like Mexican or Latino,” said Andrés Moreno-Estrada, a life sciences research associate at Stanford and the study’s lead author. “Now we’re putting finer details on that map.”
A Seri from the Gulf of California and a Lacandon Maya near the southern border are as genetically different from each other as Europeans from Chinese.
Some worry that the medical field’s focus on genetics might eclipse research on other factors that influence health. “The effects of social class on lung function have been largely ignored in favor of the focus on race and ethnic difference,” said Lundy Braun, a professor of pathology and laboratory medicine, as well as Africana studies, at Brown University. Poverty increases the risk of a host of health problems. And poorer neighborhoods have less access to parks and grocery stores that sell fresh produce.
But it’s undeniable: genes play a major role in health, even if they do so alongside other factors. The problem is that, to date, most large-scale genetic analyses have focused on European populations. “Very few studies have been done on Hispanics or Latinos,” Burchard said. So he and a team of researchers examined the DNA of more than 500 people from remote indigenous villages and cosmopolitan centers throughout Mexico, as well as Mexican Americans in California.
Mexico’s genetic tapestry turned out to be richer than they had imagined. The team’s analysis revealed that the country’s indigenous populations diverge genetically along a northwest-to-southeast axis, with variations that grow starker with distance. That means a Seri from the Gulf of California and a Lacandon Maya near the southern border are as genetically different as Europeans from Chinese.
But most people of Mexican descent aren’t indigenous, but mestizo. Would their DNA still bear the genetic signatures of their Mayan, Aztec or other indigenous ancestors, or did centuries of mixing with Spanish conquistador genes erase them forever? Surprisingly, the mestizos studied tended to have the same genetic markers as indigenous populations nearby — closely replicating the geographic differences found in indigenous DNA samples.
The findings could also guide decisions about how to allocate resources for research and care.
The researchers then examined whether the results of a lung function test (used to diagnose asthma and other respiratory problems) from kids in Mexico City and the San Francisco Bay Area reflected Mexico’s genetic diversity. (Burchard is a pulmonologist at UCSF.) Sure enough, the lungs of a mestizo with western indigenous ancestry could appear a decade younger than an equally healthy person of the same age from Yucatán, who likely has Eastern indigenous blood. That means doctors should be using different criteria to diagnose lung disease for each population.
These findings could lay the groundwork for devising precise screenings or even treatments, and guide decisions about how to allocate resources for research and care. Researchers could apply the same techniques to other regions and diagnostic tools besides lung function tests. Burchard and his colleagues published a study in 2010 correlating the amount of African ancestry participants had to their lung function — but at a much smaller scale.
The new Science study also highlights evolutionary history’s crucial, yet oft-overlooked role in biomedical research. Most population geneticists investigate patterns of human migration and variation — projects that typically receive scant funding compared to those with direct medical applications. But clinically relevant findings “are often rooted in studies that were simply curious about evolution,” said Noah Rosenberg, an evolutionary biologist at Stanford.
In the end, both medicine and evolutionary biology have unearthed the same complex genetic diversity from thousands of years of human wandering, settling, mixing. “This is driving the ball down the field toward precision medicine,” Burchard said — beyond black-and-white diagnoses.