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Three genes may play a strong role in determining why some young men raised in rough neighbourhoods or deprived families become violent criminals, while others do not, US researchers reported on Monday.
One gene called MAOA that played an especially strong role has been shown in other studies to affect antisocial behaviour - and it was disturbingly common, the team at the University of North Carolina reported.
People with a particular variation of the MAOA gene called 2R were very prone to criminal and delinquent behavior, said sociology professor Guang Guo, who led the study.
"I don't want to say it is a crime gene, but 1 per cent of people have it and scored very high in violence and delinquency," Guo said.
His team, which studied only boys, used data from the National Longitudinal Study of Adolescent Health, a US nationally representative sample of about 20,000 adolescents in grades 7 to 12. The young men in the study were interviewed in person regularly, and some gave blood samples. Guo's team constructed a "serious delinquency scale" based on some of the questions the youngsters answered.
Specific variations
"Non-violent delinquency includes stealing amounts larger or smaller than $50, breaking and entering, and selling drugs," they wrote in the August issue of the American Sociological Review. "Violent delinquency includes serious physical fighting that resulted in injuries needing medical treatment, use of weapons to get something from someone, involvement in physical fighting between groups, shooting or stabbing someone, deliberately damaging property, and pulling a knife or gun on someone."
They found specific variations in three genes were associated with bad behaviour, but only when the boys suffered some other stress, such as family issues, low popularity and failing school.
Guo said it was far too early to explore whether drugs might be developed to protect a young man. He also was unsure if criminals might use a genetic defence" in court.
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