A twin study of personality disorders

Mo twin study has previously investigated the whole range of personality di sorders (PDs) recorded by interviews. Based on twin and patient registries, 92 monozygotic (WIZ) and 129 dizygotic (DZ) twin pairs were interviewed wi th the Structured Clinical Interview for DSM-III-R Personality Disorders (S CID-II). Observed prevalence rates from a normal population study of more t han 2,000 individuals were used in combination with data from the present s tudy to generate statistics assumed to be valid for a normal twin populatio n, and these statistics were used for structural equation modeling. The bes t-fitting models had a heritability of .60 for PDs generally,.37 for the ec centric (Al cluster,.60 for the emotional (B) cluster, and .62 for the fear ful (C) cluster. Among the specific PDs, the heritability appeared to be .7 9 for narcissistic,.78 for obsessive-compulsive,.69 for borderline,.67 for histrionic,.61 for schizotypal,.57 for dependent,.54 for self-defeating,.29 for schizoid,.28 for paranoid, and .28 for avoidant PDs. The best-fitting models never included shared-in-families environmental effects. However, a model with only shared familial and unique environmental effects could not be ruled out for dependent PD. Shared familial environmental effects may al so influence the development of any PD and borderline PD. Passive-aggressiv e PD did not seem to be affected by genes or family environment at all. The low occurrence of antisocial PD in the twin sample precluded any model for this disorder. PDs seem to be more strongly influenced by genetic effects than almost any axis I disorder, and more than most broad personality dimen sions. However, we observed a large variation in heritability among the dif ferent PDs, probably partly because of a moderate sample size and low preva lence of the specific disorders. Copyright (C) 2000 by W.B. Saunders Compan y.