Vol. 9, No. 2, 2003 Page 6


Dopamine gene variant linked to externalizing behavior

One variant of a gene that affects dopamine use by the brain is linked to externalizing behavior problems in children, according to a recent study.

The term "externalizing behavior" describes chronic aggression, delinquency, and destructive, oppositional, and impulsive behavior. Children who exhibit such behavior are often treated with drugs such as methylphenidate (Ritalin), which alter the function of the dopamine transporter (DAT). This transporter's job is to terminate the activity of dopamine by transporting it from the synapsesóthe spaces between neuronsóback to the cells that released it.

Susan Young et al. investigated the role of a particular allele (variant) of the DAT1 gene, the 9-repeat allele, on children's externalizing behaviors. The 790 participants in the study were recruited through the Colorado Longitudinal Twin Study and the Colorado Adoption Project.

Evaluating data provided by parents on the children's behavior at 4, 7, and 9 years of age, Young et al. found that the 9-repeat variant of the DAT1 gene "is a significant risk allele for externalizing behavior at ages 4 and 7 years." While the association was nonsignificant at age 9, the researchers say that across the three ages, "the overall association of the 9-repeat DAT1 allele with externalizing behavior is well supported."

Some studies have also suggested that the 9-repeat DAT1 allele is a risk factor for alcohol dependence and substance abuse. A different variant of the DAT1 allele, the 10-repeat variant, is tentatively linked to attention deficit hyperactivity disorder (ADHD).

Young et al. conclude, "These findings encourage continued investigation of the role of the dopamine system in the biological basis of problem behavior."

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"Dopamine transporter polymorphism associated with externalizing behavior problems in children," Susan E. Young, Andrew Smolen, Robin P. Corley, Kenneth S. Krauter, John C. DeFries, Thomas J. Crowley, and John K. Hewitt, American Journal of Medical Genetics, Vol. 114, No. 2, 2002, 144-9. Address: Susan E. Young, Institute for Behavioral Genetics, Campus Box 447, University of Colorado, Boulder, CO 80309.

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