July 15, 2008 In one of the first studies to link molecular genetic variants to adolescent delinquency, sociological research published in the August issue of the American Sociological Review identifies three genetic predictors--of serious and violent delinquency--that gain predictive precision when considered together with social influences, such as family, friends and school processes.
Sociologists from the University of North Carolina-Chapel Hill explored the interaction of genetics and social influences and identified three genetic polymorphisms that--when examined in the context of modulating social controls--are significant predictors of delinquency. These findings about gene--environment interactions suggest that certain genotypes and specific social control influences (e.g., family characteristics and processes; popularity and friendship characteristics; and school attendance factors) are mutually dependent on delinquency.
While many behavioral studies of gene--environment interactions typically examine the relationship of a single factor (e.g., child abuse, stress) to genes, the present research is unique in that it systematically examines layers of social context simultaneously (i.e., family dynamics, peer relations, and school-related variables). The study uses regression analysis to reveal non-intuitive and complex relations among the researched variables.
"While genetics appear to influence delinquency, social influences such as family, friends and school seem to impact the expression of certain genetic variants," said Guang Guo, the study's lead author and a professor of sociology and faculty fellow at the University of North Carolina-Chapel Hill's Carolina Population Center and Carolina Center for Genomic Sciences. "Positive social influences appear to reduce the delinquency-increasing effect of a genetic variant, whereas the effect of these genetic variants is amplified in the absence of social controls."
"Our research confirms that genetic effects are not deterministic," Guo said. "Gene expression may depend heavily on the environment."
The three genetic polymorphisms that predict delinquency include:
- the 30-base pair (bp) promoter-region with a variable number tandem repeat (VNTR) in the monoamine oxidase A (MAOA) gene,
- the 40-bp VNTR in the dopamine transporter 1 (DAT1) gene and
- the Taq1 polymorphism in the dopamine D2 receptor (DRD2) gene. MAOA regulates several brain neurotransmitters important in behavioral motivation, aggression, emotion and cognition (e.g., serotonin, dopamine, norepinephrine).
Among the findings, the research suggests a conditional interaction between repeating a school grade and the MAOA*2 repeat (2R) allele in adolescent boys. For those who did not have the 2R allele, repeating a grade was significantly correlated with serious delinquency, but for those who had this 2R allele and who repeated a grade, the propensity for serious delinquency increased dramatically.
The study also indicates a link between the DRD2 gene and having daily family meals. Daily meals with one or two parents are a powerful moderator for the effect of the DRD2 gene.
"Most delinquent and violent behaviors are considered complex," Guo said. "Understanding these behaviors requires understanding both their socioeconomic-cultural components and their genetic components."
The correlation of social and genetic effects on delinquency suggests the need for the social sciences to incorporate genetic evidence in this area of study, according to Guo. The implications of these findings also raise important questions for public policy.
For this study, the researchers examined a sample of approximately 1,100 males in grades 7 through 12 whose DNA and social-control measures were available through the National Longitudinal Study of Adolescent Health. Guo co-authored the research with Michael E. Roettger and Tianji Cai, both doctoral candidates at the University of North Carolina-Chapel Hill. The research was supported in part by grants from the National Institutes of Health and the National Science Foundation.
Guo's work on genetics and delinquency has also been published in Human Genetics and has been accepted for publication in the European Journal of Human Genetics.
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