A study of 794 prisoners in Finland has identified two genes which may be partly responsible for violent crimes.
The A(MAOA) (monoamine oxidase) gene affects mood, feelings and behaviour by altering the levels of “feelgood” chemicals dopamine and serotonin in the brain.
Researchers at the Karolinska Institute in Sweden found that a low-activity version of the gene MAOA was associated with crimes committed by extremely violent offenders.
In cases of a rare genetic mutation where the MAOA gene is absent, this can lead to aggressive behaviour in an individual.
The team found that a majority of crimes committed in Finland had been committed while under the influence of amphetamines or alcohol, which temporarily increase levels of the feelgood chemical dopamine in the brain.
Low-activity MAOA means that dopamine is broken down slowly and therefore high levels of aggression in individuals with the gene variant may result when they drink alcohol or take amphetamines.
CDH13 is a gene which scientists believe influences impulsivity. The researchers found that certain variants of the gene were associated with offenders who had committed murders or were repeat offenders.
Dr Seena Fazel – the Wellcome Trust Senior Research Fellow at Oxford University’s Department of Psychiatry – said that a larger study is needed as some reviews of MAOA studies have not found a clear link with violence.
Previous research from Sweden has suggested that criminality may be inherited. Researchers looked at the records of children who had been adopted but who went on to commit criminal acts and the records of their biological parents. They found that some adopted children whose biological parents had criminal records went on to commit criminal acts themselves.
The findings of the latest Swedish study are published in the journal Molecular Psychiatry.
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