Antidepressant Response and the Serotonin Transporter Gene-Linked Polymorphic Region

BackgroundThe serotonin transporter gene-linked polymorphic region (5-HTTLPR) has been proposed as a predictor of antidepressant response. Insertion or deletion of a 44-base pair-long region gives rise to short “S” and long “L” forms of the promoter region, the “S” form being associated with reduced serotonin transporter expression.MethodsA systematic review and meta-analysis was performed to clarify the effect of 5-HTTLPR on antidepressant response and remission rates. Data were obtained from 28 studies with 5408 participants. Three genotype comparisons were tested-SS versus (SL or LL), (SS or SL) versus LL, and SS versus LL.ResultsThere was no statistically significant effect on antidepressant response. Compared with L carriers, there was an apparent effect of the SS genotype on remission rate (relative risk: .88; 95% confidence interval: .79-.98; p = .02). However, after trim and fill correction for missing data, the effect disappeared (relative risk: .92; 95% confidence interval: .81-1.05; p = .23), indicating that the initial significant effect was likely the result of publication bias. No significant effect on remission rate was seen for SS versus LL and SS/SL versus LL. Substantial unexplained heterogeneity of effect sizes was observed between studies, pointing to additional interacting factors contributing to an association in some cases.ConclusionsThe 5-HTTLPR biallelic short/long polymorphism by itself does not seem to usefully predict antidepressant response.