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Which Kids Join Gangs? A Genetic ExplanationHow much power do genes hold over behavior? Can they predict, for example, whether a child will grow up to join a gang? Those are among the questions raised by a new Florida State University (FSU) study released June 5. Since the early 1990s, science has suggested a link between antisocial behavior and a defect in the gene that codes for an enzyme called monoamine oxidase A (MAO-A). A low level of activity on the MAO-A gene results in an excessive breakdown of neurotransmitters, such as serotonin, which helps keep humans calm and happy. The defect thereby increases the urge to react aggressively to threats or fears, leading MAO-A to be referred to as the "warrior" gene. The latest research, however, takes the association one step further. It is the first to link low activity on the MAO-A allele in young men both to an increased likelihood of joining a gang and to a greater tendency to use weapons and violence. "For the first time, we were able to establish a direct connection between the MAO-A gene and the choosing of a violent lifestyle," says Kevin Beaver, a biosocial criminologist at FSU and lead author of the study published in Comprehensive Psychiatry. Researchers used DNA data and self-reported lifestyle surveys from nearly 2,500 participants in the National Longitudinal Study of Adolescent Health, the largest and most comprehensive survey of health-related behavior among adolescents between 7th and 12th grade, which started in 1994. Slightly more than half of the study's male participants had low-level activity on the MAO-A gene, and about 3% of the total pool reported having joined a named gang in the past year. Beaver and his colleagues found that those males carrying the low-active MAO-A gene were nearly twice as likely to join an organized gang than males with the high-active gene, and when in a fight, they were nearly twice as likely to brandish a weapon. Of the gang members studied, those who had a low-activity MAO-A allele were more than four times more likely to use a weapon when compared with male gang members who carried a high-activity version of the allele. "At the very least this suggests a genetic risk factor that can help us identify those youth most at risk," Beaver says. "We can then intervene earlier to prevent it." Indeed there's little doubt that violence is the result of an uneasy mix between bad genes and a bad environment. How much control nature has over nurture, however, is the question. Previous studies of the MAO-A gene suggest that interplay may begin in early childhood. A British study of 442 New Zealand men, published in 2003, was among the first to find that those with a low-active MAO-A gene, who had been abused as children, were four times more likely to have committed rapes, robberies and assaults than the general population. Those with high-active MAO-A genes, moreover, appeared to be immune to childhood mistreatment, turning out to be no more or less violent than average. Men with low-active genes who were not the victims of child abuse were slightly less antisocial than average. "What all these risk gene studies show us is that genes do an important job in loading the gun," says Joshua Buckholtz, a neuroscience Ph.D. candidate at Vanderbilt University's Brain Institute and Department of Psychology, who has written extensively about MAO-A gene. "But it's the environment that pulls the trigger." As Beaver's study shows, not all carriers of the defective MAO-A gene join a gang, and not all gang members have the defect. It remains largely unknown how common the low-active gene variant is in the general population, though one 2002 study indicated that genetic factors, including MAO-A, account for as much as 50% of the population variance in risk for antisocial behaviors. Additionally, Beaver's and other studies have found that low levels of the MAO-A enzyme affect only men, despite the fact that the MAO-A gene is located on the X chromosome. One explanation is that male-specific hormones may play a role in MAO-A expression, or that females may have other biological traits that mitigate the effect of a defect, or simply that females have two copies of MAO-A versus males' one. "Males, who have one X chromosome and one Y chromosome, possess only one copy of this gene, while females, who have two X chromosomes, carry two," Beaver says. "Thus, if a male has a variant for the MAO-A gene that is linked to violence, there isn't another copy to counteract it." Any compensation would have to come from the environment, and studies suggest that early intervention can have great impact. Researchers at the University of Georgia last month published a study of 641 adolescents, ages 11 to 16, some of whom carried the short allele form of the gene 5-HTTLPR — a genetic condition found in about 40% of the general population and long associated with low self-control, binge drinking and substance use. Half of the participants were randomly enrolled in drug prevention programs. After five years, those participants with 5-HTTLPR who were enrolled in a prevention program were no more likely than their counterparts in the comparison group, without the gene, to have engaged in drinking, smoking marijuana, and sexual activity. Youths with the gene, who were in the comparison group, were twice as likely to have engaged in these risky behaviors as their peers in the prevention group. "The findings underscore that 'nurture' can influence 'nature' during adolescence, a pivotal time when delaying the start of alcohol consumption and other risky behaviors can have a significant impact on healthy child development," said Kenneth R. Warren, acting director of the National Institute on Alcohol Abuse and Alcoholism, in a statement. Beaver cites last month's prevention study as key to understanding how to best make use of his latest findings on MAO-A and gang membership. If policymakers wish to prevent violence, he says, money would be better spent not hunting for gene-based drugs, say, but expanding and improving neighborhood-based intervention programs, such as early childhood education and after-school activities. "It's much easier and cost-effective to modulate an individual's environment than it is to alter their genetic code," says Buckholtz. And until the gene is better understood, that investment will pay off for those with the MAO-A defect and those without. 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