Background. There is extensive evidence of statistical associations between family
discord/maladaptation and antisocial behaviour in the children, but questions remain on the extent to
which the psychopathological risks are genetically or environmentally mediated.
Methods. Twin pairs (N = 1350), aged 8 to 16 years, in the general population-based Virginia Twin
Study of Adolescent Behavioral Development were assessed using the Child and Adolescent
Psychiatric Assessment interview administered separately to both twins and both parents.
Structured interviews for parental lifetime psychiatric disorders were also administered to the
mothers and fathers. Maternal reports on Olsson's Family Adaptability and Cohesiveness
questionnaire and the Dyadic Adjustment Scale were used as indices of the family environment. A
path analytical model based on an extended twin-family design was used to test hypotheses about
parent–offspring similarity for conduct disorder symptomatology.
Results. Family discord and maladaptation, which intercorrelated at 0·63, were associated with a
roughly two-fold increase in risk for conduct disorder symptomatology. When parental conduct
disorder was included in the model the environmental mediation effect for family maladaptation
remained, but that for family discord was lost.
Conclusion. It is concluded that there is true environmental mediation from family maladaptation,
operating as a shared effect, which accounts for 3·5% of the phenotypic variance. The assumptions
underlying this genetic research strategy are made explicit, together with its strengths and