Mexico Is Home to DNA That's a World Apart, Study Shows

Mexicans from different regions of the country are as genetically different as Europeans are from Asians, researchers have found.

The vast differences in the patchwork of Native American ancestry indicate that Mexicans should no longer be lumped into one homogeneous group, particularly when it comes to clinical practice, according to a report published Thursday in Science. The study was led by a group of scientists from Stanford University's School of Medicine, the University of California San Francisco (UCSF) and the Mexican National Institute of Genomic Medicine.

"When you walk into a clinic, whether you know it or not, someone makes a decision about you. Are you white, are you European, are you African, are you Asian?" says Esteban Burchard, professor of bioengineering and therapeutic sciences and medicine at UCSF. "In the U.S., one of the things we ask is, are you Hispanic?"

Now, says, Burchard, it has become clear that what is normal for one ethnic group may be borderline abnormal for another—and taking the finer details of Latino health into consideration can make the difference between an accurate diagnosis and an erroneous one.

Researchers studied lung function, in particular, and concluded that diseases such as asthma and emphysema are determined by a person's type of Native American ancestry. For example, a person in northwest Mexico would have lungs that appear approximately 12 years younger than a person of the same age and height in the country's southeast region.

Scientists also found that people of mixed European and Native American heritage—two groups that began exchanging genes some 500 years ago during the Spanish colonization—were found to have genomes corresponding to their local indigenous population. A person in the northern state of Sonora, for example, is more likely to have Seri or Tarahumara genomic components while someone from Yucatan, in the country's southeast, would probably display a Mayan gene component. These, in turn, are as genetically different as the Europeans are from the Chinese.

These results can be used to spot larger trends. "This is not just relevant to Mexico. It's relevant, number one, to all of Latin America, so a fifth of the world population. The method, the observations, are generalizable to the entire world," said Burchard.

"We're showing, for the first time on a country-wide level, genetic variation in Native American population," added Burchard.

Since most genetic studies to date have concentrated on Europeans or European Americans, researchers said, the team decided to focus this study on Native American ancestry. It was a way to both celebrate and understand a marginalized and understudied segment of the global population, says Carlos Bustamante, professor of genetics at Stanford and one of the lead authors of the study.

Mexico was a natural choice not only because it has one of the largest amounts of pre-Columbian genetic diversity in the Americas but also because some scientists in the team had already been collecting samples from the area for years. In the end, researchers utilized 1,000 samples, about half of which belonged to Native Americans and half to mestizos, or people with mixed descent. Together, scientists had nearly 1 million genetic variants to work with.

The study, its authors say, highlights the need to study populations worldwide so that the fruits of the Human Genome Project become accessible to all.

"Our hope is that we can move the needle and develop genomic medicine so that it benefits everyone, not just the populations of European descent," says Bustamante.

The findings, Burchard says, will also help advance precision medicine, a practice in which a person's genetic information is used to tailor a specific medical treatment.

Bustamante said his team plans on using the samples to study signatures of natural selection in different environments, as well as biomedical traits such as height.

About 40 experts, including researchers from Puerto Rico, Spain, France and the United Kingdom, participated in the study, which was financed by the Mexican government, the UCSF Chancellor's Research Fellowship, the American Asthma Foundation and the National Institutes of Health, among others.