SLC6A4 and major depressive disorder: • miR-132 and miR-124 regulate BDNF• miR-132 potential biomarker for MDD• miR-124 not a reliable biomarker• miR-132 consistently identified in MDD studies• SSRI treatment increases miR-16 expression and regulates SERT uptake of serotonin• Patients with low miR-1202 levels predicted to respond better to serotonin-based drugs