A twin study of personality disorders

Area of Science:

• Psychiatry and Behavioral Genetics
• Clinical Psychology
• Twin Studies

Background:

• Previous twin studies have not comprehensively examined the full spectrum of personality disorders (PDs).
• Understanding the etiology of PDs is crucial for developing effective interventions.

Purpose of the Study:

• To investigate the genetic and environmental contributions to the development of various personality disorders using a twin study design.
• To estimate the heritability of PDs generally and specific PDs within the DSM-III-R classification.

Main Methods:

• Interviewed 92 monozygotic (MZ) and 129 dizygotic (DZ) twin pairs using the Structured Clinical Interview for DSM-III-R Personality Disorders (SCID-II).
• Utilized observed prevalence rates from a large population study (over 2,000 individuals) to inform structural equation modeling.
• Employed structural equation modeling to estimate genetic and environmental influences on PDs.

Main Results:

• Overall heritability for PDs was estimated at .60, with significant genetic influence across personality disorder clusters (A: .37, B: .60, C: .62).
• Heritability estimates for specific PDs varied widely, including high heritability for narcissistic (.79) and obsessive-compulsive (.78) PDs.
• Shared familial environmental effects were generally not supported, except for potential influence on dependent and borderline PDs; passive-aggressive PD showed no genetic or familial environmental effects.

Conclusions:

• Personality disorders are substantially influenced by genetic factors, more so than many other psychiatric disorders and broad personality dimensions.
• Significant heterogeneity in heritability exists among different PDs, potentially due to sample size and prevalence.
• Non-shared environmental factors appear to be the primary environmental influence for most PDs.