A LONGITUDINAL TWIN STUDY OF 1-YEAR PREVALENCE OF MAJOR DEPRESSION INWOMEN

Objectives: This study seeks to clarify the etiologic importance and t emporal stability of the genetic and environmental risk factors for 1- year prevalence of major depression (1YP-MD) in women. Design: One-yea r prevalence of major depression was personally assessed, using DSM-II I-R criteria, at two time. points a minimum of 1 year apart. Participa nts: Both members of 938 adult female-female twin pairs ascertained fr om the population-based Virginia Twin Registry. Results: The correlati on in liability to 1YP-MD was much greater in monozygotic (MZ) than in dizygotic (DZ) twins at time 1 alone, time 2 alone, or at either time 1 or time 2. Model fitting suggested that the liability to 1YP-MD was due to additive genes and individual specific environment with a heri tability of 41% to 46% and was not biased by violations of the equal e nvironment assumption. Jointly analyzing both times of assessment usin g a longitudinal twin model suggested that, over a 1-year period, gene tic effects on the liability to 1YP-MD were entirely stable, while env ironmental effects were entirely occasion specific. Conclusions: These results suggest that (1) genetic factors play a moderate etiologic ro le in the 1YP-MD, (2) the temporal stability of the liability to major depression in adult women is largely or entirely genetic in origin, a nd (3) environmental factors play a significant role in the etiology o f major depression, but their effects are generally transitory and do not result in enduring changes in the liability to illness.