The large ethnic diversity of Mexico was something I learned about from xeos's AMA, and now a recent study has shown just how diverse the people of Mexico are. The investigators sampled the genomes of over 1000 people, representing 20 indigenous and 11 mestizo groups. They also made sure to sample all over the various regions of Mexico, as shown in figure 1C of their paper.

When they compared all these genomes, they found a tremendous amount of diversity (probably not surprising). Interestingly, they also found that the similarities tend to cluster regionally., which means historically, there hasn't been significant migration and mixing of people. From the Stanford press release:

The researchers found that Mexico's indigenous populations diverge genetically along a diagonal northwest-to-southeast axis, with differences becoming more pronounced as the ethnic groups become more geographically distant from one another. In particular, the Seri people along the northern mainland coast of the Gulf of California and a Mayan people known as the Lacandon found near the country's southern border with Guatemala are as genetically different from one another as Europeans are from Chinese.

Most importantly, they found that these differences matter in terms of health. In particular, the researchers looked at whether the forced expiratory volume in 1 s (FEV1) is an accurate measure of lung health in different groups. Typically, doctors have a "normal" range of values for FEV1, but that range can vary depending on your genetic background. The researchers confirmed this was the case here, with different genetic groups having different FEV1 values. Therefore, "normal" FEV1 ranges can't be assumed for all people equally, and genetic background will play a factor.

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In all, this shows how important it is to not lump all Mexican people into one category when performing genetic studies or recruiting for clinical trials. The genetic diversity needs to be taken into account so that we can understand how those differences matter for health.