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“Warrior gene” reported rife among young thugs

June 5, 2009
Courtesy Florida State University
and World Science staff

Boys car­ry­ing a par­tic­u­lar var­i­ant of a gene are un­usu­ally likely to join gangs—and to be among their most vi­o­lent, highly armed mem­bers, a new study has found. The re­search linked a gene called mono­amine ox­i­dase A, or MAOA, to gangs and guns.

The find­ings apply only to ma­les; girls with the same ge­net­ic pe­cu­liar­ity seem re­sist­ant to its po­ten­tially vi­o­lent ef­fects, the re­search­ers said.

Kev­in M. Bea­ver of the Flor­i­da State Un­ivers­ity’s Col­lege of Crim­i­nol­o­gy and Crim­i­nal Jus­tice, who led the stu­dy, said it probes the in­ter­play of ge­net­ics and en­vi­ron­ment that pro­duces some of so­ci­ety’s most se­ri­ous of­fend­ers.

“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,” said Bea­ver.

“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,” he said. “More­over, we found that var­i­ants of this gene could dis­tin­guish gang mem­bers who were markedly more likely to be­have vi­o­lently and use weapons” than oth­er mem­bers.

The gene var­i­ant has some­times been called the “war­rior gene,” said Bea­ver.

The gene has been found to af­fect lev­els of mood- and be­hav­ior-re­lat­ed sig­nal­ing mo­le­cules in the brain, called neu­ro­trans­mitters, such as dopamine and ser­o­to­nin. Vari­ants re­lat­ed to vi­o­lence have been found to be he­red­i­tary, re­search­ers said. Some pre­vi­ous stud­ies have found the “war­rior gene” to be more prev­a­lent in cul­tures typ­i­fied by war­fare and ag­gres­sion.

“What’s in­ter­est­ing about the MAOA gene is its loca­t­ion on the X-chro­mo­some,” Bea­ver 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. 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.”

The study ex­am­ined DNA da­ta and lifestyle in­forma­t­ion drawn from more than 2,500 re­spon­dents to the U.S. Na­tional Lon­gi­tu­di­nal Study of Ad­o­les­cent Health, a Uni­versity of North Caro­lina sur­vey of U.S. adol­es­cents in grades 7-12 dur­ing the 1994-95 school year. Bea­ver and col­leagues de­tailed their find­ings in a pa­per to be pub­lished in a forth­com­ing is­sue of the jour­nal Com­pre­hen­sive Psy­chi­a­try.


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Boys carrying a particular variant of a gene are unusually likely to join gangs—and to be among their most violent, highly armed members, a new study has found. The Florida State University research identified a link between a gene called Monoamine oxidase A, or MAOA, to gangs and guns. The findings apply only to males; girls with the same genetic peculiarity seem resistant to its potentially violent effects, the researchers said. Kevin M. Beaver of the university’s College of Criminology and Criminal Justice, who led the study, said it probes the interplay of genetics and environment that produces some of society’s most serious offenders. “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,” said Beaver. “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,” he said. “Moreover, we found that variants of this gene could distinguish gang members who were markedly more likely to behave violently and use weapons” than other members. The gene variant has sometimes been called the “warrior gene,” said Beaver. The gene affects levels of mood- and behavior-related signaling molecules in the brain, called neurotransmitters, such as dopamine and serotonin. Variants related to violence have been found to be hereditary, researchers said. Some previous studies have found the “warrior gene” to be more prevalent in cultures typified by warfare and aggression. “What’s interesting about the MAOA gene is its location on the X-chromosome,” Beaver 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. 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.” The study examined DNA data and lifestyle information drawn from more than 2,500 respondents to the National Longitudinal Study of Adolescent Health. Beaver and colleagues detailed their findings in a paper to be published in a forthcoming issue of the journal Comprehensive Psychiatry.