Regardless of drug status (quetiapine vs. placebo), there was a no effect of time on the SERT mRNA expression level across the FM and FM + MDD groups (p > 0.05) Due to loss to follow-up and missing blood samples, the SERT mRNA expression level was only analyzed in 16 MDD subjects after 8 weeks of treatment. This evidence concerns the gene SLC6A4 and major depressive disorder.