SLC6A4 and major depressive disorder: The downregulated miR-135a was shown to promote the translation of the Htr1a and Slc6a4 genes in MDD patients (Issler et al., 2014) and the upregulation of the inhibitory 5HT1a receptor (5HT1AR), encoded by the Htr1a gene, and 5HT transporter (SERT), encoded by the Slc6a4 gene, contributed to aberrant monoamine neurotransmitters in patients with depression (Issler et al., 2014).