If you happen to carry a particular variant for one of three common genes (whether you carry just one or all three), you may be more likely to engage in antisocial behavior, but only if you were exposed to an abusive or adverse environment in childhood, according to a new study.
The findings confirm previous studies that show how negative experiences can influence how genetic variants affect the brain, and therefore promote negative behavior, according to a new study.
“Evidence is accumulating to show that the effects of variants of many genes that are common in the population depend on environmental factors. Further, these genetic variants affect each other,” said researcher Sheilagh Hodgins, Ph.D., of the University of Montreal and its affiliated Institut Universitaire en Santé Mentale de Montréal.
“We conducted a study to determine whether juvenile offending was associated with interactions between three common genetic variants and positive and negative experiences,” write the researchers in the International Journal of Neuropsychopharmacology.
For the study, 1,337 Swedish teens, aged 17 to 18, anonymously completed questionnaires on delinquency, family conflict, experiences of sexual abuse, and the quality of their relationship with their parents. They also provided a sample of saliva from which the researchers extracted DNA.
The monoamine oxidase A (MAOA) gene is a key enzyme in the catabolism of brain neurotransmitters, monoamines, especially serotonin. Catabolism is the breaking down of complex materials and the releasing of energy within an organism.
“About 25 percent of Caucasian men carry the less active variant of MAOA. Among them, those who experience physical abuse in childhood are more likely than those who are not abused to display serious antisocial behavior from childhood through adulthood,” said Hodgins.
“Among females it is the high activity variant of the MAOA gene that interacts with adversity in childhood to increase the likelihood of antisocial behavior.”
Furthermore, the brain-derived neurotrophic factor (BDNF) gene controls neuronal plasticity — brain cells’ ability to reorganize pathways and connections throughout our lives.
“The low expressing variants of BDNF are carried by approximately 30 percent of individuals and some previous studies had shown that this variant was associated with aggressive behavior if carriers were exposed to aggressive peers,” said Hodgins.
The third gene studied was the serotonin transporter 5-HTTLPR. The low activity variant of this gene is carried by approximately 20 percent of individuals. Among those who carry the low activity variant, those exposed to childhood adversity are more likely to display antisocial and aggressive behavior, compared to those with healthy childhoods.
“We found that the three genetic variants interacted with each other and with family conflict and sexual abuse to increase the likelihood of delinquency, and with a positive parent-child relationship to decrease the risk of delinquency,” Hodgins said.
“Among carriers of the low activity variants of all three genes, those exposed to family conflict or sexual abuse or both reported high levels of delinquency while those who reported a positive and warm relationship with their parents reported little or no delinquency.”
Thus, the same genetic variants were associated with high and low levels of delinquency depending on exposure to negative or positive environments.
“In conclusion,” Hodgins said, “variants of three common genes, MAOA, BDNF, and 5-HTTLPR, interacted with each other and with negative environmental factors to increase the risk of delinquency. Or, when combined with a positive environment, they were able to decrease the risk of delinquency in a large sample of teenagers.
“These findings add to those from other studies to show that genes affect the brain, and thereby behavior, by altering sensitivity to the environment,” she said.
Source: Universite de Montreal