SLC1A4 and major depressive disorder: Furthermore, an integrative gene set-based GWAS meta-analysis of case–control studies of MDD revealed statistical enrichment for variants in genes involved in glutamatergic synaptic neurotransmission, including SLC1A4 [66], and reduced SLC1A4 expression has been reported in the anterior cingulate cortex and hippocampus of patients with MDD [67].