Experiences and genes are to blame for violent behaviour

December 17, 2014  17:21

You may not have been born a criminal, but a combination of genes and environment could control your fate when it comes to anti-social behaviour.

This is according to a recent study which found that experiences, such as divorce and sexual abuse, could affect gene expressions that control a person's predisposition to delinquency.

According to The Daily Mail, the study used a survey of 1,337 students aged 17 or 18 in Västmanland, Sweden, who anonymously completed questionnaires reporting on their behaviour.

As well as their behaviour, they spoke about past family conflict, experiences of sexual abuse, and the quality of their relationship with their parents.

They also provided a sample of saliva from which the researchers extracted DNA. One of the genes examined was Monoamine oxidase A (MAOA).

This gene is a key enzyme which breaks down and releases energy in brain neurotransmitters, such as serotonin. The transmitter be a contributor to feelings of well-being and happiness

'About 25 per cent of Caucasian men carry the less active variant of MAOA,' explained Professor Sheilagh Hodgins, a researcher at the University of Montreal.

'Among them, those who experience physical abuse in childhood are more likely than those who are not abused to display serious anti-social behaviour from childhood through adulthood.

'Among females it is the high activity variant of the MAOA gene that interacts with adversity in childhood to increase the likelihood of anti-social behaviour.'

Another gene examined was BDNF, which impacts neuronal plasticity. This refers to the brain cells' ability to reorganise pathways and connections throughout our lives.

'The low expressing variants of BDNF are carried by approximately 30 per cent of individuals and some previous studies had shown that this variant was associated with aggressive behaviour if carriers were exposed to aggressive peers,' said Professor Hodgins.

The third gene variant studied was the serotonin transporter 5-HTTLPR, which is carried by approximately 20 per cent of individuals.

'Among carriers of this low activity variant, those exposed to adversity in childhood are more likely than those who are not to display antisocial and aggressive behaviour,' said Professor Hodgins.

Overall, the study found that the three genetic variants interacted with each other and with family conflict and sexual abuse to increase the likelihood of delinquency.

'Among carriers of the low activity variants of all three genes, those exposed to family conflict or sexual abuse or both reported high levels of delinquency while those who reported a positive and warm relationship with their parents reported little or no delinquency,' said Professor Hodgins.

'These findings add to those from other studies to show that genes affect the brain, and thereby behaviour, by altering sensitivity to the environment,' Professor Hodgins said.

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