Antisocial behavior, drug abuse, and alcoholism tend to run in families, and a new study suggests that this is largely due to genetic transmission of a general vulnerability to externalizing disorders.
Brian Hicks and colleagues studied 542 families participating in the Minnesota Twin Family Study. All of the families consisted of 17-year-old identical or fraternal twins and their biological mothers and fathers.
The researchers found that a general vulnerability to externalizing disorders (a term encompassing antisocial behavior, conduct disorder, substance abuse, and other externally-directed behavior problems) was "highly heritable" (heritability estimate .80), while no evidence was seen for genetic transmission of specific externalizing disorders.
When the researchers compared siblings to each other, they detected an increased likelihood for the twins to exhibit similar specific problems (such as alcoholism or drug addiction). These effects were the same for fraternal and identical twins, indicating that environmental factors such as peer pressure may influence the way in which a genetic vulnerability to externalizing behaviors is expressed.
"Family transmission and heritability of externalizing disorders: a twin-family study," B. M. Hicks, R. F. Krueger, W. G. Iacono, M. McGue, and C. J. Patrick, Archives of General Psychiatry, Vol. 61, 2004, 922-28. Address: Brian M. Hicks, Dept. of Psychology, University of Minnesota, 75 E. River Rd., Minneapolis, MN 55455.