Gene-environment interactions on the course of Attention-Deficit/Hyperactivity Disorder (ADHD) symptoms: From early into late adolescence

While Attention Deficit/Hyperactivity Disorder (ADHD) symptoms often persist throughout adolescence and even adulthood, relatively little is known about determinants of the course of ADHD symptoms across adolescence. In this PhD thesis it was aimed to advance our understanding why ADHD symptoms persist into late adolescence in some individuals but not in others. More specifically, it was analyzed whether the contribution of genes, environments, and gene-environment interactions (G×E’s) on ADHD symptoms may differ across various stages of adolescence. Different environmental contexts (e.g., perinatal factors, parenting, stressors, and school/family context) were examined to obtain a more comprehensive picture of how ADHD candidate genes (i.e., DRD4, 5-HTTLPR, DRD2, COMT, and MAOA), environment, and their interaction may be involved in adolescent development.
The studies in this PhD thesis show that there is increasing support that the interplay between genes and the environment is crucial in understanding the course of ADHD symptoms. The search for specific G×E effects, as well as main effects of genes and environment, on the course of ADHD symptoms, however, still represents a complex and unfinished task. Heterogeneity in terms of the definition of variables of interest, research designs, and involved samples have to be taken into account when interpreting results and planning future studies. Overall, the specificity of G×E effects on the course of ADHD symptoms presented in our studies shows that the precision of timing of the role of genes, environment, and their interaction is a pivotal aspect in discovering determinants of the course of ADHD symptoms across adolescence.