a1 Washington VA Medical Center, Washington, DC, USA
a2 Georgetown University Medical Center, Washington, DC, USA
a3 Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA, USA
Background The relationship between personality and psychiatric illness is complex. It is not clear whether one directly causes the other.
Method In a population-based sample of male twins (n=3030), we attempted to predict major depression (MD) from neuroticism (N) and extraversion (E) and vice versa, to evaluate the causal, scar, state, and prodromal hypotheses. In a longitudinal, structural equation twin model, we decomposed the covariation between N and MD into (a) genetic and environmental factors that are common to both traits, as well as specific to each one and (b) direct causal effects of N at time 1 on subsequent MD, as well as between MD and subsequent N.
Results E was negatively correlated with lifetime and one-year prevalence of MD. N predicted the new onset of MD, and was predicted by both current and past MD. It did not predict the time to onset of MD. All of the covariation between N and MD was due to additive genetic and individual-specific environmental factors shared by both traits and a direct causal path between MD and N assessed later. No genetic factors were unique to either trait.
Conclusions In men, N may be a vulnerability factor for MD but does not cause it directly. However, MD may have a direct causal effect on N. The genetic overlap between N and MD in men may be greater than in women.
(Online publication April 04 2007)