Mental representations of attachment in identical female twins with and without conduct problems.

Insecure mental representations of attachment, a nearly invariant feature of cluster B personality disorders, have never previously been studied in twins. We conducted the Adult Attachment Interview (AAI) on 33 pairs of monozygotic (MZ) female twins reared together as an initial exploration of causal influences on mental representations of attachment. As predicted by attachment theory, we observed substantial twin-twin concordance for attachment security (odds ratio 13.8; P = 0.001), a similar level of concordance between twins and their non-twin siblings, and an inverse relationship between attachment security and current level of aggression (P = 0.01). These data indicate that there are minimal effects of non-shared environmental influences (or measurement error) on attachment classifications derived from the AAI. In this sample of twins with and without histories of Conduct Disorder, mental representations of attachment appear to be highly familial, i.e., strongly influenced by either shared environmental factors, genetic factors, or both.