In a new study, researchers have determined that prenatal exposure to cigarette smoking, when combined with a specific genetic variant, places children at increased risk for aggressive behavior and other behavioral problems.

The study, led by scientists at the Institute for Juvenile Research at the University of Illinois at Chicago, identified a long-lasting influence on a child's behavior precipitated by the monoamine oxidase A (MAOA) gene variant in conjunction with prenatal exposure to tobacco. MAOA is an enzyme which regulates key neurotransmitters in the brain. 

The genetic variant responsible for increased risk of behavioral problems differs between boys and girls, researchers said. In boys exposed to tobacco smoke prenatally, the low-activity MAOA (MAOA-L) gene variant was associated with increased disruptive social interactions, aggressive behavior, and serious rule-violating.

Among girls, the high-activity MAOA (MAOA-H) gene variant was associated with increased disruptive behavior. In addition, girls with both the MAOA-H variant and prenatal exposure to cigarette smoke had an increased "hostile attribution bias" -- a tendency to perceive anger in a range of facial expressions -- that was not seen among boys.

There was a higher risk of disruptive behavior for both boys and girls the more their mother smoked during pregnancy, according to the study.

"The tendency to over-perceive anger suggests the possibility that the combination of prenatal tobacco exposure and the MAOA risk variant affects the brain's processing of emotional cues," said Lauren Wakschlag, the study's principal investigator. "Clearly, close attention to sex differences in these patterns will be critical for future studies," she said.

The study was funded by the National Institute on Drug Abuse (NIDA).