Genetic Link Found in Some Violent Men
Study finds gene variant coupled with childhood abuse can make the difference
FRIDAY, Aug. 2, 2002 (HealthDayNews) -- A gene linked to aggressive behavior may help explain why some men who were abused as children turn to violent crime while others do not.
Men with relatively weak activity of the gene, called MAOA, who were maltreated as children are far more likely to display antisocial behaviors than their peers who also suffered abuse but have normal levels of the instruction.
Although the study suggests that weak MAOA may be a proverbial devil on the shoulder, the researchers stressed that healthy MAOA is a powerful protector from antisocial urges.
"The most exciting part to us was the fact that the abused child who had the high-acting genotype [was] very unlikely to engage in antisocial behavior," said Terrie Moffitt, a psychologist at the University of Wisconsin, Madison and a co-author of the study. "That suggests that they were protected in some way" from committing aggression.
"There must be something in one's [genes] that can make a person trauma-resistant," added Moffitt, who is also on the faculty of King's College, London.
Moffitt and her colleagues report their findings this week in the journal Science.
MAOA controls an enzyme, monoamine oxidase A, that helps break down the brain-signaling molecule serotonin. Serotonin is an important actor in many behaviors, including aggression and impulse control. MAOA also regulates two other brain chemicals, dopamine and norepinephrine.
In earlier work, scientists found that both people and mice completely lacking MAOA were prone to aggression. But they haven't seen this effect in the general population, where a total absence of the instruction and its enzyme is all but unheard of.
The new study, however, looked at the interaction of variations in MAOA and early childhood stress. Moffitt and her colleagues followed 442 New Zealand men for 26 years. Two thirds had normal levels of MAOA activity, while in a third the gene was weak.
As children, 8 percent of the men had experienced "severe" mistreatment and 28 percent has suffered "probable" abuse, which included maternal neglect and physical and sexual harm.
Men who'd been maltreated as children and who had under-active MAOA made up 12 percent of the group. But they accounted for 44 percent of the violent convictions, the researchers said. That effect, they noted, is equivalent to what high blood pressure or smoking does to a person's risk of heart disease. And of the men with low MAOA and an abusive past, 85 percent displayed antisocial behaviors.
Experts said the research illustrates the intricate interaction between genes and environment in shaping behavior.
"Many years ago, people would always be interested in whether a trait was genetic or environmental," said Scott Stoltenberg, a behavioral geneticist at the University of Michigan in Ann Arbor who has studied MAOA.
"It's not genes or environment. It's definitely an interplay between the two," particularly in complex traits where many genes are involved, he said.
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