Implications of Genetic Diversity in Mexico

Posted by Pete Shanks June 25, 2014
Biopolitical Times
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The category Latino is a valid cultural artifact, and often self-identified. But it's not really a race in any modern sense of the term, and the genetic evidence surely shows that it is far too broad a grouping to be scientifically appropriate without serious qualification. Yet it is used, even in some current peer-reviewed papers.

One that does not use the term is an article published in Science this month on the genetics of Mexico. The country's population is large and ethnically, linguistically, geographically, economically and culturally diverse. It is also genetically complex, and this article by a large and distinguished team of scientists provides new details. It also suggests some important implications for genomic research and likely for personalized medicine in general:

The genetics of Mexico recapitulates Native American substructure and affects biomedical traits

The study included 511 Native Mexican individuals from 20 indigenous groups, and 500 mestizo (mixed-race) individuals from ten states; nearly a million SNPs were analyzed for each. The variation was striking. From the abstract:

Some groups were as differentiated as Europeans are from East Asians. Pre-Columbian genetic substructure is recapitulated in the indigenous ancestry of admixed mestizo individuals across the country. Furthermore, two independently phenotyped cohorts of Mexicans and Mexican Americans showed a significant association between subcontinental ancestry and lung function.

The first implication for research is clearly that a lot more samples are needed. If this much variation was hidden in Mexico, how much may there be in pockets of Europe and Asia, let alone Africa? Somehow "the" human genome seems more elusive than ever.

That, in turn, carries implications for personalized medicine, as well as for the apparently hard-to-kill concept of genetic race. Consider another paper published this month (there is a bit of overlap among the authors) in JAMA:

Association of a Low-Frequency Variant in HNF1AWith Type 2 Diabetes in a Latino Population

This is another substantial study, and it did tease out a rare allele that is associated with an increased risk for diabetes. However, it "was observed in 0.36% of participants without type 2 diabetes and 2.1% of participants with it." In other words, the five-fold increase in risk leaves 98% of patients unaccounted for. Indeed, this may be an example of "geneticizing disease" as Michael Montoya discussed in his 2011 book Making the Mexican Diabetic.

It's worth noting, as co-author Karol Estrada points out at the Genomes Unzipped blog, that

The variant … was not found in publicly available genetic databases, including 1000 Genomes, Exome Sequencing Project, and dbSNP. Therefore, we would have missed this variant even if we had used the latest genotyping array technology and imputed (i.e., inferred the presence of) variants that were not directly genotyped.

That's yet another argument for more extensive genomic research, in particular (as Estrada stresses) among non-European populations. But the ellipses hide this apparently positive statement:

The variant was found only in people who live in Mexico or the southern U.S. and identify as Latino.

Culturally, they probably do so identify. But is it really appropriate to turn that sociopolitical category into what seems to be used as a genetic category? Even culturally, the variant may be associated with a sub-population (in which it may perhaps be significantly more common); the article suggests that all 52 carriers have "at least 1 segment of inferred Native American ancestry." It seems that the use of Latino is sloppy, at best.

Still, there may be thousands of people who have that allele, and they may have particular treatment needs. That would certainly be an appropriate use of genetic analysis in personalized medicine. But the practical difficulties remain substantial. Just for a start, and setting aside privacy and related issues: who do you test, how do you test them, who pays? Will insurance companies cover a 1-in-50 shot? And what about those with the allele but no symptoms?

Eventually, genomic analysis is likely to make an important contribution to routine medical treatment. But clearly there is quite some distance to go. And we would all be wise to avoid the tendentious use of imprecise terms.

Previously on Biopolitical Times: