Country-by-genotype-by-environment interaction in childhood academic achievement

Why children differ in their cognitive abilities, including their academic achievement, is a function of their environment and genotype, and this function may be complex, involving gene–environment (GxE) interaction and gene–environment (GE) covariation. The paper by Figlio et al. (1) in PNAS on academic achievement in reading and mathematics considers the importance of GxE interaction in a unique state-wide sample of twin children from Florida. GxE interaction can be thought of as the genetic control over sensitivity to environmental conditions or, alternatively, as the environment determining the expression of the genotype. Several scenarios may be distinguished: Across different environments, the same genes are expressed, but their absolute or relative influences vary (quantitative differences), or different genes are expressed across different environments (qualitative differences). Obviously, a combination of these two scenarios is also possible. A third alternative states that under GxE interaction, environmental influences vary conditional on a child’s genotypic value (e.g., a low or high genotypic value for mathematical ability) (2). As to how GxE interaction may manifest, several theoretical models each offer their own prediction. The diathesis-stress model predicts that genetic vulnerability, or diathesis, increases the likelihood of a trait in the presence of environmental stress. It also predicts that the heritability of the trait will be higher for children in risk environments (3). In contrast, the bioecological model predicts that risk environments will mask genetic differences between children and enriched environments will amplify genetic differences (4). In studies of human behavior, researchers usually rely on cross-sectional designs with groups of related or genotyped individuals exposed to different environments to assess quantitative and qualitative GxE interactions. Such a cross-sectional design was employed by Figlio et al. (1): Twin children’s academic achievement in mathematics and reading in primary school was observed under different socioeconomic status (SES) circumstances. Birth and … [↵][1]1To whom correspondence should be addressed. Email: di.boomsma{at}vu.nl. [1]: #xref-corresp-1-1