Genetic test may identify boys who will grow to be violent

Boys who are physically or sexually abused are far more likely to grow into violent men if they inherit a particular version of a gene controlling chemical messages in the brain.

The findings of a research project, reported in the journal Science today, identify an unusual interaction between the genetic make-up of violent men and the maltreatment they suffered as children.

The investigation of 442 men, whose education and progress was followed for 26 years, indicates that genes and upbring-ing play a critical part in predicting whether a young man is likely to become violent.

Any child who was abused was twice as likely to be violent in later life. But the study also found that carrying one version of a gene that controlled chemical messages in the brain increased this risk by nine times.

If the findings can be replicated by other scientists, they raise the prospect of using genetic tests to try to screen children from disturbed backgrounds who are at a particularly high risk of committing violent crimes later in life.

Professor Terrie Moffitt of King's College London, who led researchers from the UK, New Zealand and the US, said the results showed how a gene could affect a person depending on their upbringing. "This is not really the story of a gene that has a risk for anti-social behaviour. It's the story of the interplay between a gene and the experience of maltreatment," Professor Moffitt said.

The gene is called MAOA. It is responsible for an enzyme secreted in the brain that mops up the neurotransmitters carrying signals from one nerve cell to another. The "violent" version of the MAOA gene appears to be less efficient at doing this. "In its normal role, the enzyme has a sort of clean-up function. It stays in the synapse [nerve connection] between two neurons and clears away excess neurotransmitters. I think of it as a little Pacman," Professor Moffitt said.

A Dutch study nearly 10 years ago showed that a particular mutation in the MAOA gene was responsible for the high number of violent men in one extended family in Holland.

All the boys in the study were born in New Zealand and were part of a research project dating back to 1972, which monitored their education, parenting and criminal record.

At the age of 11, about a third had been maltreated, and although only 12 per cent of these abused boys had low MAOA activity, they accounted for 44 per cent of their generation's total convictions for assault or other violent crime.

"As adults, 85 per cent of the severely maltreated children who also had the gene for low MAOA activity developed antisocial outcomes, such as violent criminal behaviour," Professor Moffitt said. "The combination of maltreatment and the genetic variation magnified the odds by nine times."

Maltreated children who inherited the more active form of the MAOA gene seemed better able to cope with the trauma of abuse. This suggested that this version of the gene might confer resistance to stress and it might even be an advantage for people working in potentially dangerous environments.

Professor Moffitt said low MAOA activity might act as a predictive test for violent behaviour in much the same way as cholesterol testing could predict heart disease. "Low levels of the enzyme did not predict anti-social outcomes in the whole population. Its relation to aggression only emerged when we considered whether the children had been maltreated," she said.