Genographic stratification
Signs of social inequality were seen in the genes of the British
Polina Loseva, N+1
Scientists have found traces of social stratification of the UK population at the genetic level. They found out that people with similar sets of genes and the level of predisposition to certain diseases live in the same regions of the country, even if they are not relatives, and it depends on the economic well-being of the region. The study was published in the journal Nature Human Behavior (Abdellaoui et al., Genetic correlates of social stratification in Great Britain).
Until now, it was believed that different gene variants are distributed in a population approximately randomly. The Mendelian randomization method, which has recently become popular, is based on this assumption. Its essence is as follows: if certain gene variants are associated with a certain trait, then we can assume that the trait in the population is distributed randomly. And then we can check whether it is true that people with this sign are more likely to have this or that disease. And if so, then we can assume that we have established a causal relationship.
Abdel Abdellaoui from the University of Amsterdam and his colleagues discovered a pitfall in this method. They showed that genetic variants can be distributed in a population far from randomly. This could be influenced, for example, by the migration routes of people of certain social groups between countries or even within the same country.
Scientists used data from the British genetic database UK Biobank. From it, they selected 455,426 people from different regions of the UK. For each of them, a polygenic risk indicator was evaluated – this is the relative chance that a person will have one or another sign. To calculate it, scientists took a set of gene variants that may be associated with this trait and summed up the values for each gene (whether there is a "necessary" variant or not) multiplied by coefficients reflecting the significance (weight) of a particular gene.
Polygenic risk indicators were calculated by scientists for a number of signs: there were both physiological – for example, body mass index, propensity to drug addiction or risk of diabetes, and social factors – for example, the level of education. At the same time, the researchers took data on which gene variants affect traits from articles whose authors did not work with UK Biobank – to be sure that the set of these gene variants is not unique to the British.
The researchers found that polygenic risk indicators for a variety of signs are unevenly distributed across the UK. In other words, there are people in the north of the country who are predisposed to other conditions and diseases than in the south or in Wales. But even when scientists included people's pedigrees in their model as one of the factors, this effect did not disappear anywhere. This means that in different areas of the UK there are people with a similar level of risk of developing certain signs, even if they are not relatives.
People are divided into five groups (according to the values of the principal components, PC) depending on the combination of polygenic risk indicators for different signs. They occur with different frequency in different regions of the UK.
This dependence was especially strong for the level of education. The authors of the work drew attention to the fact that the polygenic risk index for the level of education was lowest (approximately -0.2 compared to 0.2 on average in the country) in the "mining" regions with a high index of economic disadvantage (Townsend index). When the researchers checked how the risk indicators for other traits were distributed across England, they found that they were very different in residents of these regions and the rest of the British. The risk indicators of people who left mining towns differed the most. For example, the polygenic risk index for body mass index was approximately 0.1 for residents of a poor region, -0.5 for residents of other regions of the country and -0.1 for those who left a poor region for a rich one.
Scientists believe that in this way they managed to fix the stratification of society at the genetic level. The more strongly a particular trait was associated with the socio-economic situation, the higher the degree of clustering of risk indicators on this trait. Probably, these are traces of industrialization: once representatives of the poor strata of society went to work in the mines and settled around them. Now poor migrants continue to arrive in these areas, and people who are interested in education and career, on the contrary, leave them.
Distribution of the polygenic risk indicator for the level of education (red) by regions of the UK (two maps on the left). The value of the Townsend index (economic distress, two maps on the right). The mining regions are circled in black.
The authors of the article note that such a manifestation of social inequality can distort the results of statistical studies – it may turn out that genetic variants are not evenly distributed in the population at all. At the same time, inequality on one basis distorts data on others. For example, one can imagine that if people have a lower polygenic risk index for the level of education, they are more likely to live in poor regions, eat unhealthy food and be obese.
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