Behavior affected by interplay between genes, environment

More evidence of the interplay between genes and environment comes from two new studies of the behavioral influence of one variant of the MAOA gene.

Monoamine oxidase A (MAOA) is an enzyme that breaks down neurotransmitters that play a role in mood, impulsiveness, pleasure, and aggression. Different variants of the MAOA gene result in higher or lower activity of this enzyme.

Growing evidence links low expression of MAOA with aggression or antisocial behavior in animals and humans. Among previous findings:

• A study in 1993 (see related article, Crime Times, 1995, Vol. 1, No. 3) found that many male members of a Dutch family with a long history of violence and aggression exhibited a mutation in the MAOA gene.
• Studies show that mice deficient in MAOA are more aggressive than their normal counterparts (see related article, Crime Times, 1995, Vol. 1, No. 3).
• Research shows that during emotional arousal, men with the low-activity variant of the MAOA gene show greater response in the amygdala (which senses threats) and lower activity in the prefrontal areas of the brain (which are involved in impulse control and regulation of emotion) compared to other men.
• According to one report, abused children with the low-activity variant of the MAOA gene are far more likely to become antisocial as adults than abused children with the high-activity variant (see related article, Crime Times, 2002, Vol. 8, No. 3).

The researchers report that aggression occurred more often when the amount of money taken rose from 20 to 80 percent. At the 20 percent level, participants with the low-activity gene variant were only slightly more likely to opt for punishment than those with the high-activity variant. However, at the 80 percent level, subjects with the low-activity variant were much more likely to opt for punishment and to choose a higher dose of hot sauce.

These findings, the researchers say, suggest that some people are more prone to punish than others, and that there may be an evolutionary logic for this behavior. The findings also support research suggesting that MAOA may play a role in interpersonal aggression, violence, political decision-making, and crime.

In a separate study, L. S. Wakschlag and colleagues evaluated 176 teens to analyze the effects of maternal smoking during pregnancy. The researchers found that boys with the low-activity variant of the MAOA gene and prenatal exposure to cigarettes were at increased risk for conduct disorder symptoms, which often lead to adult antisocial behavior. Interestingly, girls with the high-activity variant were more likely to have conduct disorder symptoms and to exhibit a hostile attribution bias on a face-processing task. The researchers say, ”Future research to replicate and extend these findings should focus on elucidating how gene x exposure interactions may shape behavior through associated changes in brain function.”

“Monoamine oxidase A gene (MAOA) predicts behavioral aggression following provocation,” Rose McDermott, Dustin Tingley, Jonathan Cowden, Giovanni Frazzetto, and Dominic D. P. Johnson, Proceedings of the National Academy of Sciences, January 23, 2009 (epub ahead of print publication). Address: Dominic Johnson, dominic.johnson@ed.ac.uk.

“’Warrior gene’ predicts aggressive behavior after provocation,” news release, Brown University, January 19, 2009.

“Interaction of prenatal exposure to cigarettes and MAOA genotype in pathways to youth antisocial behavior,” L. S. Wakschlag, E. O. Kistner, D. S. Pine, G. Biesecker, K. E. Pickett, A. D. Skol, V. Dukic, R. J. Blair, B. L. Leventhal, N. J. Cox, J. L. Burns, K. E. Kasza, R. J. Wright, and E. H. Cook, Molecular Psychiatry, March 3, 2009 (epub prior to print publication). E-mail: lwakschlag@psych.uic.edu.