Thesis defense Mireille Huvenaars (Donders series 342)

14 September 2018

Promotor: prof. dr. J. Buitelaar
Co-promotors: dr. C. Greven, dr. J. Glennon

Aggression in male adolescents. The role of genetic, cognitive and hormonal factors

When most people think of aggression, they think of road rage, physical fights, and violent crime. However, not all aggression is bad. Aggression may be adaptive by for example, helping people and animals alike guard their homes from intruders and protect their children from threats. Problems arise when aggression is taken too far, escalating abnormally in a repeated way and becoming violent.

The multiplicity of factors associated (i.e. environmental, genetics, (neuro)endocrine, cognitive, and behavioural factors) with the emergence, development and maintenance of aggressive behaviour suggests that aggression is a complex behaviour involving many different processes. Additionally, these factors may all be associated with each other, which makes unravelling the underlying mechanisms even more complicated. Insights of different mechanisms may help to identify more homogeneous subgroups for development and or improvement of customized medical and/or psychological treatments. Current research on psychological treatments in particular, show a modest effect on reducing (severe) aggressive behaviour, which may in part be a result of the heterogeneity of both across and within clinical disorders. This issue could be tackled by increased insights of biomarkers which may help to identify more homogeneous subgroups. As human molecular genetic studies of aggression are in an early stage, the strongest molecular evidence comes from animal models comparing aggressive and non-aggressive strains or documenting the effect of gene knockouts. Furthermore, individuals with either ODD/CD or ASD, or without a clinical disorder partially differed on (neuro)endocrine and (neuro)cognitive factors. More specific, hormonal concentrations, emotion processing, time to first fixation and fixation duration were different between disorders. However, we do not know if these findings are unique to ODD/CD and ASD or whether they reflect a deficit that cuts across those with psychopathology relative to TDI. An additional clinical group without core deficits in empathy could further add to the significance of our findings. The work in this thesis contributes to enhancement of understanding and knowledge of trans-diagnostic markers based on scientific research focused on both a diagnostic and a dimensional approach. In the longer term, current and future research results will contribute to reduce the impact of adaptive aggression on society.