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Khethelo Xulu
Understanding random acts of violence
Author: Engela Duvenage
Published: 15/06/2017

Why do some people commit violent crimes seemingly just for fun? Have they had particularly bad childhoods, or are they in some way "pre-programmed" to simply get their kicks from vicious aggression?

In his PhD research, Khethelo Xulu uses his knowledge of molecular biochemistry and genetics to investigate this phenomenon of so-called appetitive aggression. His work forms part of efforts by the SARChI Chair in Posttraumatic Stress Disorders (PTSD) in the Department of Psychiatry to understand how violence and trauma affect South Africans, and why some people cope better than others.

"Those who perpetrate acts of appetitive aggression seem not to be traumatised by what they see and hear while committing such offences, and feel comfortable in unsafe and cruel environments," Xulu explains. His PhD is supervised by Dr Sian Hemmings, Prof Soraya Seedat and Dr Stefanie Malan-Muller.

Xulu's study is the first on the topic to be conducted in a South African population of young male former offenders. Genetic samples were taken from 290 Xhosa men and the 5-HTT gene was assessed. It plays a role in transporting serotonin, a neurotransmitter that influences how people respond to stress. 

Xulu and his co-researchers found no link between aggressive behaviour and specific genetic variations in the serotonin transporter (5-HTT) promoter region of the particular participants.

However, there seems to be an association between appetitive aggression and the presence of the intron 2 (STin2) 10-repeat allele. This bit of genetic material is linked to a low expression of 5-HTT, and in the process to a dysregulated, poorer response to stress. Its presence is linked to a greater likelihood of novelty seeking behaviour and aggressive deeds, as well as a heated temperament.

"Knowing more about the molecular mechanisms and genetic architecture of essential genes that encode for neurotransmitters helps us understand the molecular underpinnings involved in how appetitive aggression and other mental health disorders develop.

"This is particularly important in finding out how PTSD and aggression behaviours develop in a uniquely South African population," Xulu says.

Caption: Khethelo Xulu is investigating a phenomenon called appetitive aggression.