Abstract

Background We know little about the degree to which comorbidity, so commonly seen among psychiatric disorders, arises from variation in normal personality. Aims To study the degree to which variation in normal personality accounts for the comorbidity of eight common psychiatric and substance use disorders. Method Internalising disorders (major depression, generalised anxiety and panic disorders, phobias), externalising disorders (alcohol and drug dependence, anti-social personality and conduct disorders) and personality dimensions of neuroticism, extraversion and novelty seeking were assessed in 7588 participants from a population-based twin registry. The proportion of comorbidity explained by each personality dimension was calculated using structural equation modelling. Results Neuroticism accounted for the highest proportion of comorbidity within internalising disorders (20–45%) and between internalising and externalising disorders (19–88%). Variation in neuroticism and novelty seeking each accounted for a modest proportion (10–12% and 7–14%, respectively) of the comorbidity within externalising disorders. Extraversion contributed negligibly Conclusions High neuroticism appears to be a broad vulnerability factor for comorbid psychiatric disorders. Novelty seeking is modestly important for comorbid externalising disorders.