Gene-Environment Interaction in Adolescent Deviant Behaviour

Abstract: The overall aim of this thesis was to explore gene-environmental (G'E) interactions in relation to deviant behaviour among 200 Swedish adolescents, with a focus on criminality, alcohol consumption and depressive symptoms. Those behaviours have been extensively investigated in relation to both psychosocial and biological risk factors. The biological markers used were the monoamine oxidase (MAO-A) and serotonin transporter (5-HTTLPR) gene polymorphisms.The main findings indicated a considerable gene-environment interaction in relation to all outcome variables studied. Individuals with the long/short variant of the 5HTTLPR gene, in combination with unfavourable family relations, both consumed more alcohol and had 12-14 times higher risks of being classified as high alcohol consumers.The MAO-A gene showed a G'E interaction related to criminality. Among boys, the short allele predicted an increased risk for criminality, whereas among girls, it was the long allele, if they lived in multi-family houses and/or had been maltreated, assaulted or sexually abused.A G'E interaction in relation to depressive symptoms among both boys and girls was determined. Girls carrying the short 5HTTLPR allele in combination with psychosocial stress, presented elevated depressive symptoms, whereas among boys, the long 5HTTLPR allele was a source of depressive symptoms. In both sexes, there was a G'E interaction of a psychosocial risk index. Girls were more affected by poor family relations and boys by multi-family housing and separated parents.In conclusion, the MAO-A and 5HTTLPR genotypes, in interaction with psychosocial adversity, are related to different deviant behaviours among adolescents. The direct effects of the genotypes needed to be adjusted for the psychosocial factors, whereas the psychosocial factors had direct relation to the outcome measures. There is also an indication of a different pattern in G'E interaction between boys and girls and that different psychosocial factors affect boys and girls differently.