Background: Major depressive disorder (MDD) occurs in a subset of patients receiving interferon-alpha treatment, although many are resilient to this side effect. Genetic differences in the serotonin reuptake transporter promoter (5-HTTLPR) may interact with the inflammatory system and influence depression risk.
Methods: A cohort of 71 nondepressed hepatitis C patients about to receive interferon-alpha was prospectively followed, employing a diagnostic structured clinical interview (Structured Clinical Interview for DSM-IV Axis I Disorders [SCID-I]) and self-report questionnaires. Patients were genotyped for the 5-HTTLPR (L(G), L(A), and S) and the variable number of tandem repeats (VNTR) polymorphism in the second intron. Kaplan-Meier analyses were used to compare major depression incidence. Genotype effects on sleep quality (Pittsburgh Sleep Quality Index) and Beck Depression Inventory (BDI) were assessed using mixed-effect repeated-measure analyses.
Results: The L(A) allele was associated with a decreased rate of developing MDD (Mantel-Cox log rank test p < .05) with the L(A)/L(A) genotype being the most resilient. This genotype was also associated with better sleep quality [F(61.2,2) = 3.3, p < .05]. The ability of baseline sleep quality to predict depression incidence disappeared when also including genotype in the model. Conversely, the relationship of neuroticism with depression incidence (B = .07, SE = .02, p < .005) was not mitigated when including genotype.
Conclusions: Using a prospective design, 5-HTTLPR is associated with MDD incidence during interferon-alpha treatment. Preliminary evidence that this effect could be mediated by effects on sleep quality was observed. These findings provide support for a possible interaction between inflammatory cytokine (interferon-alpha) exposure and 5-HTTLPR variability in MDD.