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Family transmission and heritability of externalizing disorders: a twin-family study.

BACKGROUND
Antisocial behavior and substance dependence disorders exact a heavy financial and human cost on society. A better understanding of the mechanisms of familial transmission for these "externalizing" disorders is necessary to better understand their etiology and to help develop intervention strategies.


OBJECTIVES
To determine the extent to which the family transmission of externalizing disorders is due to a general vs a disorder-specific vulnerability and, owing to the genetically informative nature of our data, to estimate the heritable vs environmental nature of these transmission effects.


DESIGN
We used structural equation modeling to simultaneously estimate the general and specific transmission effects of 4 externalizing disorders: conduct disorder, adult antisocial behavior, alcohol dependence, and drug dependence.


SETTING
Participants were recruited from the community and were interviewed in a university laboratory.


PARTICIPANTS
The sample consisted of 542 families participating in the Minnesota Twin Family Study. All families included 17-year-old twins and their biological mother and father.


MAIN OUTCOME MEASURES
Symptom counts of conduct disorder, the adult criteria for antisocial personality disorder, alcohol dependence, and drug dependence.


RESULTS
Transmission of a general vulnerability to all the externalizing disorders accounted for most familial resemblance. This general vulnerability was highly heritable (h2 = 0.80). Disorder-specific vulnerabilities were also detected for conduct disorder, alcohol dependence, and drug dependence.


CONCLUSIONS
The mechanism underlying the familial transmission of externalizing disorders is primarily a highly heritable general vulnerability. This general vulnerability or common risk factor should be the focus of research regarding the etiology and treatment of externalizing disorders.