Issler et al. (2014) reported lower levels of miR-135a in the raphe nuclei of suicide victims as compared to control subjects and the same results were also found at peripheral level (in the whole blood); in parallel, they demonstrated alterations in miR-135a target genes involved in the regulation of Serotonin (5-HT) neuron-related genes such as the 5-HT transporter, SLC6A4, and the 5-HT receptor, HTR1A, suggesting a role for miR-135a as a potential blood biomarker for depression vulnerability (Issler et al. 2014). This evidence concerns the gene SLC6A4 and depressive disorder.