Can a gene variant make you more likely to join a gang?

Boys with low-activity variants of a gene that determines MAOA activity are more likely than other boys to join gangs and use weapons, according to a new study.

MAOA (monoamine oxidase A) is an enzyme that breaks down several neurotransmitters (messenger chemicals) that affect mood and aggression. Low-activity variants of the MAOA gene decrease MAOA function.

Kevin Beaver and colleagues studied data collected from 1,155 females and 1,041 males participating in the National Longitudinal Study of Adolescent Health. The researchers divided participants into two groups: those with low MAOA activity (2- or 3-repeat alleles) and those with high activity (3.5-, 4-, and 5-repeat alleles). The researchers found that for males but not for females, “The low MAOA activity alleles conferred an increased risk of joining a gang and using a weapon in a fight.” Males with low-activity alleles were 1.94 times more likely to be gang members, and 1.82 times more likely to have used a weapon in a fight, than those with high-activity alleles.

In addition, the researchers report, male gang members with low-activity alleles were 4.37 times more likely to use a weapon than male gang members with high-activity alleles. This finding is intriguing, they say, because “it indicates that variation in violence among gang members may be partially circumscribed by genotype.”

The lack of an association between MAOA and gang membership or violence in women is not surprising, the researchers say, because MAOA is X-linked. This means that the gene’s effects will be strongest for males, who only have one copy of the gene.

The first clues pointing to MAOA’s role in violence emerged in 1995, when a study by H. G. Brunner (see related article, Crime Times, 1995, Vol. 1, No. 3, Page 1) linked a mutation in a gene coding for MAOA to impulsive aggression in the male members of an extremely violent family. In 2002 (see related article, Crime Times, 2002, Vol. 8, No. 4, Page 1), Avshalom Caspi and colleagues studied people abused as children and found that those with a low-activity MAOA gene variant were extremely likely to become antisocial adults, while those with higher MAOA activity almost never grew up to be antisocial. And in 2008 (see related article, Crime Times, 2008, Vol. 14, No. 2, Page 2), Guang Guo and colleagues found that men with a rare low-activity variant (2R) of the gene reported levels of serious delinquency and violent delinquency in adolescence and young adulthood “that were about twice as high as those for participants with the other variants.” Women showed a similar but weaker pattern.

Beaver says, “While gangs typically have been regarded as a sociological phenomenon, our investigation shows that variants of a specific MAOA gene . . . play a significant role.” He and his colleagues suggest that males with low MAOA activity may be more attracted to violence and seek out gangs for that reason—or, conversely, that the most violent teens are sought out by certain gangs.

(see Editor’s note: Crime Times, 2009 Vol. 15, No. 3 Page 2.)

“Monoamine oxidase A genotype is associated with gang membership and weapon use,” Kevin M. Beaver, Matt DeLisi, Michael G. Vaughn, and J. C. Barnes, Comprehensive Psychiatry, May 5, 2009 (epub prior to print publication). Address: Kevin M. Beaver, kbeaver@fsu.edu.

“FSU study links ‘warrior gene’ to gang membership, weapon use,” news release, Florida State University, June 5, 2009.