a1 Department of Psychology, University of Oslo, Norway
a2 Center for Child and Adolescent Mental Health, Eastern and Southern Norway and Nic Waal's Institute, Norway
a3 Division of Mental Health, Norwegian Institute of Public Health, Norway
a4 Division of Psychiatry, University of Chicago, IL, USA
a5 Institute of Psychiatry, University of Oslo, Norway
a6 Department of Epidemiology, Columbia University, New York, NY, USA
a7 Departments of Psychiatry and Human Genetics, Medical College of Virginia of Virginia Commonwealth University, Richmond, VA, USA
Background The personality disorders (PDs) in the ‘dramatic’ cluster B [antisocial (ASPD), histrionic (HPD), narcissistic (NPD) and borderline (BPD)] demonstrate co-morbidity. However, the degree to which genetic and/or environmental factors influence their co-occurrence is not known and, with the exception of ASPD, the relative impact of genetic and environmental risk factors on liability to the cluster B PDs has not been conclusively established.
Method PD traits were assessed in 1386 Norwegian twin pairs between the age of 19 and 35 years using the Structured Interview for DSM-IV Personality Disorders (SIDP-IV). Using the statistical package Mx, multivariate twin models were fitted to dimensional representations of the PDs.
Results The best-fitting model, which did not include sex or shared family environment effects, included common genetic and environmental factors influencing all four dramatic PD traits, and factors influencing only ASPD and BPD. Heritability was estimated at 38% for ASPD traits, 31% for HPD traits, 24% for NPD traits and 35% for BPD traits. BPD traits had the lowest and ASPD traits the highest disorder-specific genetic variance.
Conclusion The frequently observed co-morbidity between cluster B PDs results from both common genetic and environmental influences. Etiologically, cluster B has a ‘substructure’ in which ASPD and BPD are more closely related to each other than to the other cluster B disorders.
(Received August 30 2007)
(Revised December 24 2007)
(Accepted January 09 2008)
(Online publication February 14 2008)