a1 Department of Biological Psychology, Vrije Universiteit, Amsterdam, The Netherlands
a2 Department of Psychiatry, Vrije Universiteit Medical Center, Amsterdam, The Netherlands
Background The association between life events and anxious depression might be due to causality or to gene–environment correlation. We examined unidirectional and reciprocal causality and a gene–environment correlation model, in which genes that influence the vulnerability for anxious depression also increase the risk of exposure to life events. The effect of genes that influence environmental exposure might be mediated through personality and we therefore also examined the association between life events and personality (neuroticism and extraversion).
Method Information on life events, anxious depression, neuroticism and extraversion was collected in 5782 monozygotic (MZ) and dizygotic (DZ) twins who participated in a longitudinal survey study of the Netherlands Twin Register. To examine causality, data were analysed longitudinally. To examine gene–environment correlation, the co-twin control method was used.
Results Anxious depression and, to a lesser extent, neuroticism scores increased after exposure to life events. Anxious depression and neuroticism also predicted the experience of life events. Prospectively, extraversion was not associated with life events. Anxious depression, neuroticism and extraversion scores did not differ between the non-exposed subjects of MZ and DZ twin pairs and unrelated subjects discordant for life events.
Conclusions Our findings suggest that reciprocal causation explains the relationship between life events and anxious depression and between life events and neuroticism. Extraversion is not related to life events. No evidence was found for gene–environment correlation, i.e. the genes that influence anxious depression, neuroticism or extraversion do not overlap with the genes that increase the risk of exposure to life events.
(Received June 07 2007)
(Revised January 08 2008)
(Accepted January 14 2008)
(Online publication February 25 2008)
c1 Address for correspondence: Dr C. M. Middeldorp, Department of Biological Psychology, Vrije Universiteit Amsterdam, Van der Boechorststraat 1, 1081BT, Amsterdam, The Netherlands. (Email: Cm.email@example.com)