Genetics of impulsive-aggressive behavior: ready for application in forensic psychiatry?

Abstract

Impulsive-aggressive behavior was demonstrated to have a substantial genetic component, thus genetic variants affecting key neuro-modulators of aggressive behavior (in particular, serotonin, dopamine, sex steroids, glucocorticoids and arginin vasopressin) are putative biological markers of violent criminal behavior. From this scenario the hypothesis of engineering genetic tests for application in forensic psychiatry arose, with the aim to define a genetic risk profile which may represent an objective proof and affect chargeability.

A number of studies investigated genes involved in the molecular pathways of the reported neuro-modulators, but results were mainly inconsistent or not replicated. Only some genes were quite consistently associated with impulsive-aggressive behavior (SLC6A4 and MAOA, which are pivotal for serotonin balance in the brain), but the explained variance was estimated not over 5% for the genetic variant with the highest evidence of association (5-HTTLPR). The described results reflect the complexity of human traits such as aggressiveness and impulsiveness, which show a biological liability due to multiple genetic variants but are subjected also to a critical influence from the environment (especially during childhood). In conclusion, biological liability due to genetic variants has not a deterministic value for violent criminal conducts. An integrated approach including biological, psychological and social variables seems the most appropriate for the investigation of human motivated behavior, even if the respective contribution of each variable and the best methodology for their investigation are still under discussion.