Criminal behaviour linked to genes

Scientists have discovered a gene that they say makes some boys more likely to turn into violent criminals than others.

They have also found that a different version of the same gene makes some people more emotionally able than others to deal with traumatic events. In the future, they predict, the Army, police and firefighters may be able to select applicants with the "trauma-resistant" gene.

The Medical Research Council team looked at the gene, which produces an enzyme called monoamine oxidaseA, or MAOA.

The enzyme ensures a healthy balance of brain chemicals that regulate mood, memory and libido and produce feelings of satisfaction and pleasure.

The team then analysed levels of MAOA in 442 men who had been maltreated in childhood. Neglect or abuse in childhood is seen as a major factor in increasing the risk of crime and violence in later life but the researchers wanted to see if genetic make-up also played a part in criminality.

They found that men with a variation of the gene that produced low levels of MAOA were much more likely to have become violent offenders than those with the "high activity" gene.

Only 12 per cent of the men had the "low activity" gene - but they accounted for 44 per cent of all the violent crimes committed by the entire study group.

Study author Professor Terrie Moffitt said: "The results provide evidence that a person's genetic make-up can influence their sensitivity to environmental factors.

"These findings may explain why not all victims of maltreatment grow up to victimise others - some genes may actually promote resistance to stress and trauma."

The researchers say the high-level type of MAOA gene may protect against effects of stress or trauma. A third of the population have the low-activity gene, and the findings could help pinpoint which maltreated children are most likely to turn to crime and violence.

The MAOA gene may explain why men are more prone to violence and aggression than women. The gene is found on the X chromosome, of which women have two to men's one. A woman may have the low level on one X chromosome but the high-activity version on the second.

Graeme Sandell, mental health spokesman for criminal justice charity Nacro, said: "This is fascinating. But we should avoid simplistic conclusions that a tendency towards criminality is locked into a person's genes."