Stressful life events and the serotonin transporter gene (5-HTT) in recurrent clinical depression

Background
An interaction between recent stressful life events (SLEs) and a serotonin transporter promoter polymorphism (5-HTTLPR) in depression has been inconsistently reported. Some of this variability may be due to a previous focus on sub-clinical depression, inclusion of individuals at the lower or upper ends of the age-span, or assumptions concerning the degree of dominance of the low expressing allele. Therefore, a large sample of patients with recurrent clinically diagnosed depression and controls screened for absence of depression was utilised to examine the moderating effect of each 5-HTTLPR genetic model on the association between SLEs and severe depressive episodes.

Method
A sample of 1236 recurrent unipolar depression cases and 598 age-matched, never psychiatrically ill controls completed the List of Threatening Experiences Questionnaire to assess the number of SLEs experienced in the 6 months prior to the most severe depressive episode (cases) or interview (controls). DNA extracted from blood or cheek swabs was genotyped for the short (s) and long (l) alleles of 5-HTTLPR.

Results
A greater number of SLEs were reported by cases than controls and this held across all genotypic groups. There was no main effect of 5-HTTLPR on depression and no evidence of interaction between total SLEs and any of the 5-HTTLPR genetic models. The results were the same for men and women.

Limitations
Utilisation of retrospective self-reported SLEs may have reduced the accuracy of the findings and the cross-sectional design prevents causal inference.

Conclusions
This study failed to find evidence of gene–environment interplay in recurrent clinical depression.