May 14, 2010 | 10
As store-based distribution of genetic health tests remains stalled pending federal review, genetic ancestry tests are also drawing widespread concern from experts.
A task force report commissioned by the American Society for Human Genetics and led by Charmaine Royal of the Institute for Genomic Sciences & Policy at Duke University has called for better research and reporting in both academic and public genetic ancestry tests.
Some 40 companies currently offer personal genetic ancestry tests, but results and interpretations are troublingly variable, the task force found. "The very concept of ‘ancestry’ is subject to misunderstanding in both the general and scientific communities," the task force members wrote.
Scientists who research population histories have trouble sorting out definitive answers about geographic origins and ancient migrations—and they generally work with larger, more statistically weighty samples rather than with data from a single individual. Although databases of reference genetic sequences are growing rapidly, many of the major studies have been done from the Human Genetic Diversity Panel, with only about 1,100 genetic samples from across the globe, which means that even much of the vetted academic work on human ancestry is still far from conclusive.
For most individuals, genetic ancestry tests hold the promise of pinpointing where their ancestors came from. Unfortunately, science has not yet caught up to this expected—and sometimes promised—level of precision. The estimates of geographic ancestral origins are based on basal "ancestral" populations from, for instance, Northern Europe, Asia, Africa or North America. However, as the task force report authors pointed out, most of these genetic population maps are actually based on best estimates of original populations, because "we do not have the ability to sample ancestral populations." Instead, proxy populations have been used, including the Yoruba people of western Africa to represent most African-American ancestry. So even if an individual’s ancestors did hail from somewhere in western Africa, if their particular lineage (as captured in their sample) does not match up with reference sequences, some tests will turn up with no family tie.
The variety of testing methods—based on mtDNA, Y chromosome markers and autosomal DNA variants—and analyses can produce results with vastly different interpretations. Scans for haploid genetic markers can indicate a common paternal ancestor, but "they reflect only a fraction of any person’s total genetic ancestry," the authors noted. And even autosomal marker scans, which "represent a much greater proportion of genome history," still miss large portions of ancestral code because as ancestors become more distant, fewer of their genetic indicators remain, decreasing the odds that they will be found in a DNA test, Royal and colleagues reported.
With all of these big unknowns, even with the best statistics, "rarely can definitive conclusions about ancestry be made beyond the assessment of whether putative close relatives are or are not related," such as in a paternity test. So any link to specific historical figures uncovered by genetic ancestry testing, whether it is Queen Elizabeth I or Ghengis Khan, is "merely speculative."
Margin of error and statistical uncertainty are expected and usually accounted for in assessing results in an academic setting. But for results on an individual ancestry test, "interpretation often is key," the report authors noted, "because the information that is presented might have direct psychosocial and other implications for the individual." Individual and even political decisions (such as claiming rights to heritage or even citizenship) are increasingly based on genetic ancestry findings, but legal precedents have yet to be consistent in interpreting these results. The task force called for greater standardization in analysis methods but also in reporting, so that ancestry results would be delivered—and perhaps interpreted—with the proper amount of essential uncertainty.
As sales of genetic tests for health and medical profiles in brick-and-mortar stores remain in limbo pending review by the U.S. Food and Drug Administration, both those tests and genetic ancestry tests remain available for the public to purchase online.
The report authors were confident, however, that the field would continue to grow in both popular participation and scientific significance, making an impact on how people view ancestry, geography and race. It could eventually "dispel the notion of race in humans." Or it could just prompt more people to ask their doctors what their newfound ancestral identities mean for their chances of getting hypertension (a use of these tests the authors did not support).
The report was published May 14 in The American Journal of Human Genetics.
Image of human migration patterns and major mtDNA haplogroups (as seen from Antarctica) courtesy of Wikimedia Commons/mitomap.org