Antisocial Behaviour and Depressed Mood: Associations from Adolescence to Adulthood

Antisocial behaviour and depression co-occur more often than would be expected by chance. Different mechanisms may account for the association including shared risk factors, shared genetic effects and causal developmental pathways from one trait to another. Identifying mechanisms involved in the association of antisocial behaviour and depression is imperative given that this might indicate approaches to treating these serious disorders. Many studies have addressed cross-sectional associations, with limited research on the longitudinal association. In this thesis, three studies were carried out to investigate the association between antisocial behaviour and depressed mood at three different time points (mean ages: 15, 17, and 20 years). The analyses are based on the G1219 longitudinal study of 3,640 adolescent twins and siblings. In the first study (Chapter 2), longitudinal associations were examined to investigate the directionality of the association between the two traits using cross-lagged autoregressive pathway models. Strong cross-sectional associations were found, in addition to significant cross-trait association from depressed mood to oppositionality. In the second study (Chapter 3), a multivariate genetically informative design (Cholesky decomposition) was used to investigate these strong cross-sectional associations. Overlapping genetic effects were found between antisocial behaviour and depressed mood. Considering the results of the second study, the third study (Chapter 4) investigated the role of functional variants of candidate genes (GNβ3, 5HTTLPR and COMT) in the association between both traits. Only GNβ3 was associated with depressed mood, however none of the candidate genes examined showed associations with both antisocial behaviour and depressed mood. Overall, the findings from the first two studies supported phenotypic and genetic overlaps. However, results of third study did not provide evidence on the overlap between the traits. Further replication with additional genetic variants in different age groups is pertinent to uncover the mechanisms involved in the association.