DNA Can Boost Anti-social Behavior

A combination of certain genetic variants and environmental factors can lead to anti-social behavior, a new study suggests.

Both negative and positive experiences influence how genetic variants affect the brain and thereby behavior, The Times of India reported. 

"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," explained Sheilagh Hodgins of the University of Montreal and its affiliated Institut Universitaire en Sante Mentale de Montreal. 

Researchers analyzed data from a group of 1,337 high school students aged 17 to 18 years old in Vastmanland, a Swedish County. Participants completed questionnaires reporting on delinquency, family conflict, experiences of sexual abuse, and the quality of their relationship with their parents. They also provided saliva sample.

Results showed that three genetic variations interact with each other and with environmental factors to increase or decrease the likelihood of delinquency, according to Fox News.

The Monoamine oxidase A (MAOA) gene is a key enzyme in the catabolism -- the breaking down of complex materials and releasing of energy within an organism -- of brain neurotransmitters.

"About 25% 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 behaviour from childhood through adulthood," Hodgins explained. "Among females it is the high activity variant of the MAOA gene that interacts with adversity in childhood to increase the likelihood of antisocial behaviour." 

The brain-derived neurotrophic factor (BDNF) gene modulates neuronal plasticity -- our brain cells' ability to reorganize pathways and connections throughout our lives.

"The low expressing variants of BDNF are carried by approximately 30% of individuals and some previous studies had shown that this variant was associated with aggressive behaviour if carriers were exposed to aggressive peers," Hodgins said.

The third gene studied was the serotonin transporter 5-HTTLPR.

"The low activity variant of this gene is carried by approximately 20% of individuals. Among carriers of this low activity variant, those exposed to adversity in childhood are more likely than those who are not to display antisocial and aggressive behaviour." 

The study showed that variants of three common genes, MAOA, BDNF, and 5-HTTLPR, interacted with each other and increased the risk of delinquency with negative environmental factors while positive environmental factor decreased 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 behaviour, by altering sensitivity to the environment," Hodgins said.