MAOA is the gene which has caught the researchers' attention with its particular connection with anti social behavior. People who had a specific variation of the MAOA gene, called 2R, portrayed an inclination for criminal and delinquent behavior, according to sociology professor Guang Guo, who led the study.
Explaining the connection, he said, "I don't want to say it is a crime gene, but 1 percent of people have it and scored very high in violence and delinquency."
Researchers studied data from the National Longitudinal Study of Adolescent Health, of 20,000 adolescent boys between grades 7 to 12.
The young men in the study had to answer several questions which were evaluated. Blood samples of the boys were collected regularly for tests. The researchers charted out a "serious delinquency scale" depending upon the questions answered by the youngsters.
Explaining the scale they said, "Nonviolent delinquency includes stealing amounts larger or smaller than $50, breaking and entering, and selling drugs. Violent delinquency includes serious physical fighting that resulted in injuries needing medical treatment, use of weapons to get something from someone, involvement in physical fighting between groups, shooting or stabbing someone, deliberately damaging property, and pulling a knife or gun on someone."
Researchers found that three genes stood out by their variation, - the monoamine oxidase A (MAOA) gene, the dopamine transporter 1 (DAT1) gene and the dopamine D2 receptor (DRD2) gene. These genes also had a connection with aberrant behavior that was portrayed only when the boys were subjected to stressful situations at home or in school.
MAOA is in charge of controlling chemicals called neurotransmitters, which play the role of a messenger and also influence emotions.
"These results, which are among the first that link molecular genetic variants to delinquency, significantly expand our understanding of delinquent and violent behavior, and they highlight the need to simultaneously consider their social and genetic origins," the researchers said.