How do genes get outside the skin? Mechanisms underlying Gene×Environment interactions in child externalizing problems

Over the past 15 years developmental scientists gained much insight into individual differences in how (strongly) children react to their surroundings. Specifically, we learned much about specific candidate genes that possibly contribute to individual differences in the strength of the relation between environmental risk factors and psychopathology (i.e., candidate gene-by-environment interactions or cG×E). The initial stage of cG×E research has yielded an interesting set of results, detecting many interaction effects between genetic polymorphisms and environmental adversity predicting externalizing behaviors. Although research on cG×E was originally received with great enthusiasm, it is now heavily criticized. Among the most important points of criticism are: that research on cG×E has not yielded reliable and replicable results; that the methods used to test cG×E are flawed; that so far it has taught us little about how genes might contribute to the development of psychopathology; and that it has given us little to no useful knowledge for clinical practice. In this dissertation we aimed to address these critiques by: (1) creating an overview of the literature (Chapter 2) and extending previous findings on cG×E with a randomized controlled trial (the ORCHIDS study; Chapters 3-6); (2) gaining more insight into how these interactions might work by formulating theory-based hypotheses on possible mechanisms underlying cG×E (Chapter 2); and (3) by testing hypothesized underlying mechanisms using two experiments (Chapters 3-7).