MAOA genotype, maltreatment, and aggressive behavior: the changing impact of genotype at varying levels of trauma.

Background: Childhood adversity has been shown to interact with monoamine oxidase-A (MAOA) genotype to confer risk for antisocial behavior. Studies examining this gene-by-environment (G x E) association, however, have produced mixed results.

Methods: Relevant research is reviewed, and results of a study with 114 children (73 maltreated and 41 control subjects) are presented. The maltreated children represent the extreme on a continuum of adversity and were assessed at a time of extreme stress-shortly after removal from their parents' care due to abuse. Measures of aggressive behavior were obtained using standard research instruments, and monoamine oxidase-A MAOA genotypes were obtained from saliva-derived DNA specimens. Population structure was controlled for using ancestral proportion scores computed on the basis of genotypes of ancestry informative markers.

Results: Many prior investigations appear to have had reduced power to detect the predicted G x E interaction because of low base rates of maltreatment and antisocial behavior in their samples and failure to use optimal procedures to control for population structure in ethnically diverse cohorts. In this investigation, a significant interaction was detected between exposure to moderate trauma and the "low-activity" MAOA genotype in conferring risk for aggression. Children with exposure to extreme levels of trauma, however, had high aggression scores regardless of genotype.

Conclusions: Our study suggests that problems in aggressive behavior in maltreated children are moderated by MAOA genotype, but only up to moderate levels of trauma exposure. Extreme levels of trauma appear to overshadow the effect of MAOA genotype, especially in children assessed at time of acute crisis.