Gene-environment interplay in internalising and externalising psychopathology in adolescence

A combination of genetic and environmental factors working in interplay is thought to underlie differences in symptoms of psychopathology between adolescents. Yet, studies that have investigated gene-environment interaction in isolated aspects of developmental psychopathology lack robust effects, highlighting the need for a more comprehensive approach. We adopted a multivariable framework to investigate gene-environment interaction in internalising and externalising symptoms of psychopathology in a sample of 3,337 16-year-olds from the Twins Early Development Study. We used penalised regression models to examine the main effects of genetic factors (G), indexed combining 13 polygenic scores for psychopathology, and environmental factors (E), measured by combining multiple environmental exposures during childhood and adolescence, on symptoms of psychopathology. We also examined their additive effects (G+E) and their interaction (GxE). Polygenic scores accounted for, on average, 2.7% of the variance in symptoms of psychopathology, with stronger predictions for externalising symptoms, while environmental measures alone accounted for an average of 7.1% of the variance. G+E accounted for an average of 9.1% of differences between adolescents in symptoms of psychopathology. We observed small GxE effects for internalising symptoms, accounting for an average of 1.1% of the variance. Children with a higher genetic risk showed higher levels of internalising symptoms, especially when exposed to more chaos at home and harsher parenting. Our findings indicate that genetic and environmental influences contribute additively, underscoring the importance of jointly considering both factors to enhance our understanding of youth psychopathology. At the same time, our results highlight the persistent challenges involved in identifying robust GxE effects.