Vol. 6, No. 2, 2000 Page 5

Conduct disorder: research on twins shows strong influence of genes

Your genes influence how smart you are, how tall you are, and how athletic you are-and a recent study indicates that they also strongly influence whether or not you have conduct disorder.

Symptoms of conduct disorder include lying, stealing, bullying, fighting, cruelty to animals and people, property destruction, and truancy. The disorder, diagnosed in childhood or adolescence, is a powerful risk factor for adult criminality.

Frederick Coolidge and colleagues studied 70 monozygotic (identical) and 42 dizygotic (fraternal) twins between the ages of 4 and 15. The researchers assessed their subjects to determine how often specific personality disorders occurred in one or both mem mbers of each twin pair. Using this data, the researchers calculated how much of the variance could be accounted for by genetics rather than by environmental factors.

Of the disorders studied, conduct disorder was one of the most highly genetically influenced, with a hereditability estimate of 68 percent. Coolidge et al.’s data are consistent with those from an earlier large-scale twin study by Wendy Slutske (see related article, Crime Times, 1997, Vol. 3, No. 3, Page 1), which reported a hereditability estimate of 71 percent for conduct disorder.

Borderline personality disorder, another disorder frequently associated with antisocial behavior, also was powerfully influenced by genes (63 percent). Overall, the mean hereditability estimate for personality disorders was 58 percent.

Coolidge notes that except for passive-aggressive personality disorder, all personality disorders defined by the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) were influenced by genes. That is why, he says, personality disorders do on’t just “pop up” in adulthood, but rather reveal themselves early on in children “as soon as their genes make the push.”

Coolidge et al.’s findings were reported at the annual meeting of the American Psychological Association.


“Personality disorders may be genetic,” Kathryn DeMott, Clinical Psychiatry News, Vol. 27, No. 12, December 1999, p. 27.

Related Article: [2000, Vol. 6] [2001, Vol. 7]

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