Male teens who possess the short variant of the monoamine oxidase (MAO)
gene are twice as likely to be gang members as are male teens who have the
long variant of the gene.
So reported Kevin Beaver, Ph.D., an assistant professor at Florida State
University College of Criminology and Criminal Justice, and his colleagues
online, on May 5, in Comprehensive Psychiatry.
Their study included some 2,000 teens equally divided by gender. They
evaluated the teens for the presence of the short or long variant of the MAO
gene. They also determined whether the teens were members of a gang, and if
so, whether they used a weapon in a
The researchers then looked to see whether they could find any link between
possessing the short MAO gene variant and being a member of a gang. They found
no such link in the female teens, but they did in the males.
The gender difference is understandable, Beaver told Psychiatric
News, because the short MAO gene variant had already been linked with a
spate of antisocial behaviors in males (Psychiatric News, November 3,
2006; December 1, 2006; August 1, 2008).
But another study finding did surprise him, he said. It was that among male
gang members, those who use weapons in a fight are more likely to have the
short MAO gene variant than are those who do not use weapons in a fight. In
other words, it looks as if "the MAO gene can distinguish the most
violent gang members from the less violent ones," he said.
What are the implications of these new findings? "A lot of research
has revealed that the short MAO gene variant only has effects on the
antisocial behavior of males who were maltreated or neglected as a
child," replied Beaver. "This means that the environment controls
the genetic effect.... [So] it stands to reason that the short MAO gene
variant would only lead to gang membership among males growing up in
crime-ridden areas where gangs are widespread. Obviously we can't change
genes, but we can change their effects by altering the environment. In other
words, intervention efforts should focus on the environment. By successfully
changing the environment, the criminogenic effects of the MAO gene could also
Exactly why researchers have only been able to link the short MAO gene
variant with antisocial behavior in males is not clear. The MAO gene is
located on the X chromosome. Females, of course, have two copies of the X
chromosome, in contrast to males having only one. So it could be that in
females, a long MAO gene variant on one X chromosome might compensate for the
effects of a short MAO gene variant on the other X chromosome, Beaver
The study was funded by the National Institute of Child Health and Human
Development and other agencies.
An abstract of "Monoamine Oxidase A Genotype Is Associated
With Gang Membership and Weapon Use" can be accessed at<www.sciencedirect.com>.
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