Aggressive behavior: The role of genetic effects in conjunction with childhood maltreatment experiences The MAOA gene Polymorphism and the Dopamine Transporter DAT1

 ABSTRACTBackground: Experiences of childhood maltreatment are usually associated with serious physical and mental health problems in adulthood and contribute to considerable costs for society in general. Still, it is clear that there is individual variation among victims of childhood maltreatment in terms of aggression behavior later in life.Aims: The general aims of the current thesis were to explore the role of two candidate genes in combination with childhood maltreatment experiences on subsequent aggressive behavior. These candidate genes were two well-studied functional variable number tandem repeats (VNTR) polymorphisms: 1) The Monoamine Oxidase-A gene (MAOA) upstream VNTR polymorphism; and 2) The dopamine transporter gene (DAT1) VNTR.Subjects: Analyses were based on participants were a subset of the second data collection of the population-based Genetics of Sexuality and Aggression (GSA) survey conducted in 2006. All Finnish-speaking twin pairs residing in Finland born between July 22, 1973, and March 1, 1988, as well as of their siblings 18 years or older, were contacted by mail. In total, the sample consists of 3626 individuals (1,447 male and 2,179 female twins and their siblings).Methods: Survey data of childhood maltreatment, aggressive behavior were obtained from the above mentioned sample using previously well-validated psychological tests. The Monoamine Oxidase-A MAOA gene polymorphism was tested as a candidate gene for the moderation of the effects of childhood maltreatment on aggressive behavior. In addition, the DAT1 gene polymorphism was tested for association with experiences of childhood maltreatment.Results: Through showing the results we found that, older participants reported less aggression when compared to younger participants. Also, older women reported less experience of childhood emotional abuse compared to younger women.

The results indicated that younger participants more frequently had experiences of childhood physical abuse compared to older participants. Importantly, participants reported a correlation between childhood maltreatment (physical and emotional abuse) and aggressive behavior (physical and verbal aggression) in adulthood. Regarding the genetic results, they showed that only in women, there was a main effect of the MAOA gene polymorphism on physical aggression. Thus, women with the high activity variant of the MAOA gene polymorphism tended to show higher levels of physically aggressive behaviors than women carrying the low activity variant of the MAOA gene polymorphism. Additionally, the results indicated a higher sensitivity to childhood maltreatment in the presence of the low activity variant of the MAOA polymorphism, i.e. we found an interaction between the MAOA gene polymorphism and experiences of childhood emotional abuse on physical aggression. Also, the results showed that men with the DAT1 gene polymorphism's 10R10R repeat allele had a higher risk for experiences of childhood sexual abuse. Whereas with women the DAT1 gene polymorphism 9R10R repeat allele revealed a higher risk for experiences for childhood emotional abuse.Conclusions: The results indicate that experiences of childhood maltreatment havedifferent effects on adult aggressive behavior for women, depending on their genetic variant on the MAOA gene polymorphism. While, the findings suggest that variants of the DAT1 gene are linked to some, but not all, types of child abuse and that these associations differ between men and women.