Study traces Mexican ancestry to decode health problems

An extensive study decoding the genes of modern Mexicans has revealed their genetic links to the pre-Columbian world of their forebears who lived in Mexico hundreds to thousands of years ago.
Wherever they may live now - in Mexico or beyond - their genes trace back to their earliest homelands and may play a key role in understanding their lives in terms of health and illness today, the study reveals.
Because so many diseases can be traced at least in part to genetic aspects, the new study led by researchers at Stanford University and UCSF could prove important to the diagnosis and medical care of everyone with even a hint of ancient Mexico in their family tree, the scientists say.
"There is tremendous genetic diversity among Mexicans and Mexican Americans, and one reason we undertook this study is that so much of what we've known until now has been based only on Europeans," said Carlos D. Bustamante, a Stanford geneticist and a lead researcher.
"Now we can see that diversity in the structure of Mexico's population and in its biomedical history."
Using the tools of the Human Genome Project, the researchers studied the genetic makeup of more than 1,000 people of Mexican ancestry in their home country and in Los Angeles. They found a million genetic markers leading to various regions of Mexico where their ancient ancestors - such as the Mayans, the Olmec, the Aztecs and many others - are known to have lived.

Link to various regions

Most people of Mexican ancestry are aware of their heritage, but the study shows for the first time their genetic connection to the various regions of their original homelands and ancient predecessors.

 "This study is about much more than Mexico," said Esteban Gonzalez Burchard, a UCSF physician who cares for children with asthma at clinics there and is one of the leading researchers. "It's putting the spotlight on one's genetic ancestry, and that can be clinically relevant at a time when we're moving down the field toward what I call precision medicine."
For example, the new findings reveal that Mexicans living in specific regions of the country are likely to carry the ancestral genes for susceptibility to lung function diseases, such as asthma and emphysema, he said.
Those genetic markers are called "single nucleotide polymorphisms," also known as SNPS, pronounced "snips."
"The real power of these studies is that we can begin to see that it's the genetics of individual populations that are important medically, regardless of the labels like race that we put on them," Bustamante said.
More than five years ago, Bustamante and John Novembre of UCLA led a similar genetic study of 3,000 Europeans and determined that their genes mirrored their ancestral origins throughout Europe, regardless of where they live now. Results of that study were published in the journal Nature.

Human Genome Project

In the Human Genome Project that was completed 11 years ago, scientists uncovered many millions of those DNA markers. For this study, detecting a million markers in 20 groups of indigenous people and 11 mestizo populations was crucial to understanding the genetic diversity of the people of modern Mexico, the researchers said.
Among their more interesting findings, the researchers said, was the discovery that the genes of many Mexican people known a mestizos - those with mixed Native American and European ancestry - can also be linked not only to people living in specific regions of Mexico where their ancestral nations once held sway, but to Africans of long ago. A report on the research by the international team of 40 scientists, including 12 from Mexico's National Institute of Genomic Medicine, is being published Friday in the journal Science.

David Perlman is The San Francisco Chronicle's science editor. E-mail: dperlman@sfchronicle.com