Introduction
Education is a key determinant of an individual’s life outcomes, influencing everything from career prospects and earning potential to health and longevity. Understanding the factors that shape educational attainment is therefore of great importance, both for individuals and for society as a whole.
Recent advances in genomic research have revolutionized our understanding of the genetic basis of educational attainment. Genome-wide association studies (GWAS) have identified thousands of genetic variants associated with years of schooling completed, allowing the construction of powerful polygenic scores that can predict a substantial proportion of the variation in this trait.
However, the interpretation of these polygenic scores is not straightforward. They capture not only the direct effects of an individual’s own genetic makeup, but also indirect effects mediated through the family environment. This is because parents pass on both their genes and the environment in which their children are raised, creating a correlation between offspring genotype and rearing environment – a phenomenon known as passive gene-environment correlation.
In this article, we explore the estimation of direct and indirect polygenic effects on educational attainment using data from the UK Biobank. We also investigate gene-environment interactions, examining how the predictive power of polygenic scores varies depending on the family environment in which individuals are raised.
Estimating Direct and Indirect Polygenic Effects
The UK Biobank is a large, population-based cohort study that has collected detailed genetic and phenotypic data on over 500,000 participants. For our analysis, we focused on the 381,654 individuals of European ancestry who had complete data on educational attainment, measured as years of schooling completed.
To disentangle the direct and indirect effects of polygenic scores, we took advantage of the UK Biobank’s data on adopted individuals. When children are adopted by non-relatives, the correlation between their genotype and rearing environment is broken, allowing us to estimate the direct effects of polygenic scores free from the confounding influence of passive gene-environment correlation.
Our analysis proceeded in several steps:
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We first estimated the heritability of educational attainment in the full sample of UK Biobank participants, using both genomic-relatedness-based restricted maximum likelihood (GREML) and linkage disequilibrium score regression (LDSC). This provided an estimate of the total (direct plus indirect) genetic contribution to variation in years of schooling.
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We then repeated the heritability analysis separately for the 6,311 adopted individuals and a matched sample of 6,500 non-adopted individuals. This allowed us to quantify the proportion of the polygenic score’s predictive power that is due to direct genetic effects, as opposed to indirect effects mediated through the family environment.
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Finally, we constructed polygenic scores for educational attainment using the summary statistics from a large meta-analysis of GWAS studies. We compared the predictive power of these scores in the adopted and non-adopted samples, testing whether the family environment amplifies the influence of genetic propensities for education.
Our results reveal that around 30% of the predictive power of polygenic scores for educational attainment is attributable to direct genetic effects, with the remaining 70% due to passive gene-environment correlation. This implies that a substantial portion of the association between polygenic scores and educational outcomes is driven by the family environment, rather than an individual’s own genetic makeup.
Interestingly, we also found that the predictive power of polygenic scores was significantly lower among adopted individuals compared to their non-adopted peers. For example, the polygenic score explained 7.4% of the variation in years of schooling in the non-adopted sample, but only 3.7% in the adopted sample.
These findings highlight the importance of the family environment in shaping the expression of genetic propensities for education. When individuals are raised by their biological relatives, their genetic predispositions are amplified by the correlated family environment. In contrast, when the link between genotype and rearing environment is broken through adoption, the direct effects of genetics become more apparent.
Exploring Gene-Environment Interactions
Our results also shed light on the complex interplay between genes and environment in the context of educational attainment. To further investigate these gene-environment interactions, we conducted a series of additional analyses.
First, we tested for an interaction between adoption status and polygenic scores in predicting years of schooling. We found a statistically significant interaction, indicating that the association between polygenic scores and educational attainment was weaker among adopted individuals compared to non-adopted individuals.
We then explored this interaction in more detail by dividing the polygenic score distribution into deciles and comparing the mean years of schooling between adopted and non-adopted individuals within each decile. Strikingly, we found that the largest difference emerged at the lowest end of the polygenic score distribution. Adopted individuals in the bottom decile of genetic propensity for education attained, on average, significantly more years of schooling than their non-adopted counterparts in the same decile.
This suggests that for those with the weakest genetic predispositions for education, a supportive adoptive environment can provide a significant boost to educational outcomes. In contrast, the family environment appears to have less impact on individuals with stronger genetic propensities, whose educational attainment is more strongly shaped by their own genetic makeup.
Implications and Conclusions
The findings from this study have important implications for our understanding of the mechanisms underlying educational attainment. They highlight the crucial role of the family environment in mediating the expression of genetic propensities, and suggest that interventions targeting the home environment may be particularly beneficial for individuals with lower genetic predispositions for education.
At the same time, our results caution against simplistic interpretations of polygenic scores. While these scores can predict a substantial proportion of the variation in educational attainment, a large part of this predictive power is due to passive gene-environment correlation, rather than direct genetic effects. This underscores the need to adopt a nuanced, multifaceted approach to understanding the determinants of educational success.
Overall, this research represents an important step forward in unraveling the complex interplay between genes and environment in shaping one of the most consequential life outcomes. By leveraging the natural experiment of adoption, we have been able to disentangle direct and indirect polygenic effects, providing valuable insights that can inform both scientific understanding and real-world interventions.
For parents and educators, the key takeaways are:
- Genetic propensities for education are not destiny – a supportive family environment can significantly boost educational outcomes, especially for those with lower genetic predispositions.
- Polygenic scores, while powerful predictors, do not solely reflect an individual’s innate ability. They also capture the influence of the family environment, which can amplify or dampen genetic effects.
- A comprehensive, multifaceted approach to supporting educational achievement is necessary, considering both genetic and environmental factors.
To learn more about the genetic basis of educational attainment and how it interacts with the family environment, visit the Stanley Park High School website. There you will find additional resources and information on this important topic.
