A LONGITUDINAL TWIN STUDY OF PERSONALITY AND MAJOR DEPRESSION IN WOMEN

Objective: To elucidate the nature of the etiologic relationship betwe en personality and major depression in women. Design: A longitudinal t win design in which twins completed a time 1 questionnaire and, 15 mon ths later, were personally inter-viewed for the occurrence of major de pression during the last year and completed a time 2 questionnaire. Bo th questionnaires contained short forms assessing neuroticism and extr aversion. Participants: 1733 twins from female-female pairs ascertaine d from the population-based Virginia Twin Registry. Results: Extravers ion was unrelated to lifetime or 1-year prevalence of major depression . Neuroticism was strongly related to lifetime prevalence of major dep ression and robustly predicted the prospective 1-year prevalence of ma j or depression in those who, at time 1, denied previous depressive ep isodes. However, controlling for levels of neuroticism at time 1, leve ls of neuroticism at time 2 were moderately elevated in those who had had an episode of major depression between times 1 and 2 (''scar'' eff ect) and substantially elevated in those experiencing an episode of ma jor depression at time 2 (''state'' effect). In those who developed ma jor depression, levels of neuroticism did not predict time to onset. I n the best-fit longitudinal twin model, the proportion of the observed correlation between neuroticism and the liability to major depression that is due to shared genetic risk factors was estimated at around 70 %, that due to shared environmental risk factors at around 20%, and th at due to a direct causal effect of major depression on neuroticism (v ia both ''scar'' and ''state'' effects) at around 10%. Approximately 5 5% of the genetic liability of major depression appeared to be shared with neuroticism, while 45% was unique to major depression. Conclusion : In women, the relationship between neuroticism and the liability to major depression is substantial and largely the result of genetic fact ors that predispose to both neuroticism and major depression.