July 17 (HealthDay News) -- It's not environment or genetics that determine a predisposition toward delinquent behavior in adolescents, it's the combination of the two, say scientists who seem to have proof of the phenomenon.

Reporting in the August issue of the American Sociological Review, researchers from the University of North Carolina-Chapel Hill point to three genetic polymorphisms that, when paired with social factors, can predict future serious and violent delinquency.

After sorting through DNA and social-control information for more than 1,100 males in grades 7 through 12, the researchers found interactions among specific genes and such environmental influences as repeating a school grade or having family meals each day.

Social sciences should probably take account of genetic information when studying juvenile delinquency, the authors stated. Public policy makers may also want to take the two realms into account.

"While genetics appear to influence delinquency, social influences such as family, friends and school seem to impact the expression of certain genetic variants," study author Guang Guo, 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, said in a university news release. "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 added. "Gene expression may depend heavily on the environment."

SOURCE: American Sociological Association, news release, July 14, 2008