Maternal education and prenatal smoking associations with adolescent executive function are substantially confounded by genetics

Twin studies have suggested extremely high estimates of heritability for adolescent executive function, with no substantial contributions from shared environment. However, developmental psychology research has found significant correlations between executive function outcomes and elements of the environment that would be shared in twins. It is unclear whether these seemingly contradictory findings are best explained by genetic confounding in developmental studies, or limitations in twin studies which can potentially underestimate shared environment. In this study, we use genetic and phenotypic data from 5939 participants, 4827 participant mothers and 2903 participant fathers in the Millennium Cohort to examine the role of genetics in explaining common environmental associations with executive function, assessed by the spatial working memory task (SWM) and Cambridge Gambling task (CGT). Bivariate GCTA revealed that single nucleotide polymorphism (SNP) effects were the sole significant predictor of the association between SWM and both maternal education and prenatal smoking. M-GCTA and trioGCTA also found no significant evidence of indirect genetic effects on SWM, indicating that genetic nurture is unlikely to explain the bivariate GCTA results. The CGT showed no significant SNP heritability, suggesting that genetic influences on hot executive function may differ significantly from those on cool executive function. This study supports the twin study claim that the working memory component of executive function is primarily a genetic trait with minimal influence from shared environment, emphasizing the importance of using genetically sensitive designs to ensure that genetic confounding does not falsely inflate estimates of environmental influences on traits.