1. ¹Clinical and Molecular Psychobiology, Department of Psychiatry and Psychotherapy, University of Würzburg, Würzburg, Germany
2. ²Institute for Forensic Psychology and Psychiatry, University of the Saarland, Homburg, Germany
3. ³Department of Child and Adolescent Psychiatry, University of the Saarland, Homburg, Germany
4. ⁴Department for Psychiatry, The School of Medicine, University of Wales, Swansea, UK

Correspondence: Dr A Reif, Clinical and Molecular Psychobiology, Department of Psychiatry and Psychotherapy, University of Würzburg, Füchsleinstr. 15, D-97080 Würzburg, Germany. Tel: +49 931 201 76000; Fax: +49 931 201 77550; E-mail: a.reif@gmx.net

Received 19 June 2006; Revised 10 January 2007; Accepted 15 January 2007; Published online 7 March 2007.

Abstract

Aggressive behavior is influenced by variation in genes of the serotonergic circuitry and early-life experience alike. The present study aimed at investigating the contribution of polymorphisms shown to moderate transcription of two genes involved in serotonergic neurotransmission (serotonin transporter, 5HTT, and monoamine oxidase A, MAOA) to the development of violence and to test for gene–environment interactions relating to adverse childhood environment. A cohort of 184 adult male volunteers referred for forensic assessment participated in the study. Each individual was assigned to either a violent or a nonviolent group. Logistic regression was performed and the best-fitting model, with a predictive power of 74%, revealed independent effects of adverse childhood environment and MAOA genotype. High environmental adversity during childhood was associated significantly with violent behavior. Forty-five percent of violent, but only 30% of nonviolent individuals carried the low-activity, short MAOA allele. Most interestingly, an interaction effect between childhood environment and 5HTT genotype on violent behavior was found in that high adversity during childhood impacted only the later-life violence if the short promoter alleles were present. These findings indicate complex interactions between genetic variation of the serotonergic circuitry and environmental factors arguing against simplistic, mono-causal explanations of violent behavior.