'Warrior Gene' Linked to Antisocial Behavior

Nancy A. Melville

January 18, 2016

A polymorphism of the monoamine oxidase A gene (MAOA) is linked to a greater risk for antisocial behavior among young men who were exposed to violence or maltreatment in childhood, new research shows.

"We found, as has been shown before, that having the genetic moderation of the MAOA gene tends to exacerbate antisocial behaviors in individuals who were exposed to an adverse environment in early childhood," first author Isabelle Ouellet-Morin, PhD, professor with the School of Criminology at the Université de Montréal, in Canada, told Medscape Medical News.

"It really appears to be a marker of genetic vulnerability to the environment," she said.

The study was published in the January issue of the British Journal of Psychiatry.

Previous Link to Aggression

Dubbed the "warrior gene," a form of the MAOA gene has been linked in previous research to aggressive behaviors. It has been theorized that the causal mechanism is the breakdown of monoamine transmitters, such as serotonin and dopamine.

The form of the gene linked to antisocial behaviors is an allele with low enzymatic activity. It is present in approximately 30% of men.

Results of previous studies of the gene's effect on behavior have been inconsistent. Dr Ouellet-Morin and her colleagues evaluated longitudinal outcomes among 327 men in the Quebec Longitudinal Study of Kindergarten Children, which included data collected over 15 years.

Investigators found higher levels of conduct disorder in adolescence and of antisocial behavior in adulthood, including a higher probability of arrest and partner violence, among those who had been exposed to violence in childhood, such as parental maltreatment and sexual and physical abuse.

Importantly, those with the MAOA polymorphism were more likely to engage in antisocial behaviors compared with those who had been maltreated as children but who did not carry the polymorphism.

"Low-frequency allele carriers had more conduct disorder and antisocial personality symptoms and reported more partner violence in comparison with high-frequency allele carriers," the authors note.

The findings are consistent with theories that genetic liabilities are more likely to emerge in response to exposure to adverse circumstances. A 2009 study showed that aggressive behavior in maltreated children was moderated by the MAOA genotype.

That study concluded that the effect seen in association with moderate levels of exposure to trauma was less than was seen in cases of exposure to extreme levels of trauma.

Dr Ouellet-Morin cautioned that much more needs to be understood about the mechanisms behind such genetic findings before interventions can be developed to help prevent aggressive or antisocial behavior.

"There are no immediate clinical implications that can really be drawn from this," she said.

"What we have done is only set the table, showing a relationship between this gene and social behavior, but this reminds us that the relationship is very complex, and there is still a lot of work to be done to understand the biological mechanisms that underlie the association."

Dr Ouellet-Morin has disclosed no relevant financial relationships.

Br J Psychiatry. 2016;208:42-48. Abstract


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