Importance of selected ABCB1 SNPs for the level of severity of depressive symptoms and effectiveness of recurrent depressive disorder therapy.

The expression level of mRNA and also the function of P-gp are strictly connected with the polymorphic nature of the ABCB1 gene. In this study, we evaluated the association between promoter SNP, i.e. T-129C, three other SNPs investigated earlier and ABCB1 expression in the depression group. To assess the additive significance of these SNPs on clinicopathological features a mathematical model was also built. 102 patients suffering from recurrent depressive disorder (rDD) and 94 healthy individuals from a local blood bank were enrolled in this study. ABCB1 gene polymorphism was identified by the RFLP method. The relative level of ABCB1 expression was measured by real-time PCR. For SNP T-129C no statistically significant differences in allele and genotype frequencies between depression and control groups were found (p = 0.3176). There was no statistically significant association between the expression value and 4 studied SNPs in ABCB1 (T-129C, C1236T, G2677T/A and C3435T) or the investigated clinicopathological features. Furthermore, a correlation between the initial HDRS score (lower than 23) and presence of at least 1236 T allele was observed, in particular in combination with 3435 T or 2677 T/A. Mutated allele of each SNP was also significantly associated with declined response to antidepressant therapy, both individually and in combination with others. Results of this study suggest that T-129C does not play an important role in the rDD development. The influence of the studied SNPs on ABCB1 gene expression is still unknown. However, the additive impact of 3 most frequently studied SNPs of ABCB1 on the course of depression and effectiveness of its treatment was confirmed.