WEDNESDAY, June 17, 2009 (HealthDay News) -- Bad neighborhoods and lack of opportunity are usually blamed for boys joining violent street gangs. But a new study finds that the urge to join gangs might lie, at least in part, in their genes.
Boys who have a variant of the gene monoamine oxidase A (MAOA) -- otherwise known as the "warrior gene" -- are not only more likely to be in gangs than boys without the variant, but they tend to be among the most violent members.
Boys with the MAOA variant are also more likely to get into fights and use weapons, according to the study.
Though the drive to join gangs is typically blamed on socioeconomic and environmental factors, from poverty to unstable families to boys' quest for a sense of belonging, the study found that joining gangs also has a genetic underpinning.
"While gangs typically have been regarded as a sociological phenomenon, our investigation shows that variants of a specific MAOA gene, known as a 'low-activity 3-repeat allele,' play a significant role," the study's lead author, Kevin M. Beaver, a biosocial criminologist at Florida State University's College of Criminology and Criminal Justice, said in a university news release.
"Previous research has linked low-activity MAOA variants to a wide range of antisocial, even violent, behavior, but our study confirms that these variants can predict gang membership," Beaver said. "Moreover, we found that variants of this gene could distinguish gang members who were markedly more likely to behave violently and use weapons from members who were less likely to do either."
The study is available in the online edition of Comprehensive Psychiatry.
For their research, Beaver and his colleagues analyzed DNA and lifestyle data from more than 2,500 teens who participated in the National Longitudinal Study of Adolescent Health.
The MAOA gene is believed to affect levels of neurotransmitters such as dopamine and serotonin that are related to mood and behavior, according to the study. Previous research found that the "warrior gene" is more prevalent in cultures that are typified by warfare and aggression.
Though the study included both boys and girls, only boys with the MAOA gene variant showed an increased propensity for violence. The gene variant had little impact on the girls, possibly because the MAOA gene is located on the X-chromosome, the researchers said.
"As a result, 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 said. "Thus, if a male has an allele (variant) for the MAOA gene that is linked to violence, there isn't another copy to counteract it. Females, in contrast, have two copies, so even if they have one risk allele, they have another that could compensate for it."
He added, "That's why most MAOA research has focused on males, and probably why the MAOA effect has, for the most part, only been detected in males."
The National Youth Violence Prevention Resource Center has tips for keeping kids out of gangs.