Stressful life events and genetic liability to major depression: genetic control of exposure to the environment?
KENNETH S. KENDLER a1 and LAURA KARKOWSKI-SHUMAN a1
a1 Departments of Psychiatry and Human Genetics, Medical College of Virginia, Richmond, VA, USA
Background. Although overwhelming evidence suggests that genetic and environmental risk factors both contribute to the aetiology of major depression (MD), we know little of how these two risk factor domains inter-relate. In particular, can the genetic liability to MD increase the risk of experiencing stressful life events (SLEs)?
Methods. Using discrete time survival analysis in a population-based sample of 2164 female twins, we examined whether the risks for nine personal and three aggregate network SLEs were predicted by the level of genetic liability to MD, indexed by the lifetime history of MD in monozygotic and dizygotic co-twins.
Results. Genetic liability to MD was associated with a significantly increased risk for six personal SLEs (assault, serious marital problems, divorce/breakup, job loss, serious illness and major financial problems) and one network SLE (trouble getting along with relatives/friends). This effect was not due to SLEs occurring during depressive episodes. Similar results were found using structural equation twin modelling. In contrast to the pattern observed with MD, the genetic liability to alcoholism impacted on the risk for being robbed and having trouble with the law.
Conclusion. In women, genetic risk factors for MD increase the probability of experiencing SLEs in the interpersonal and occupational/financial domains. Genes can probably impact on the risk for psychiatric illness by causing individuals to select themselves into high risk environments.
Address for correspondence: Dr Kenneth S. Kendler, PO Box 980126, Richmond, VA 23298-0126, USA.