SLC6A3 and major depressive disorder: The present study investigated the association between HHV-6 infection and specific genetic factors [SLC6A3 (g.1394961C>T, rs40184), BDNF (g.27658368C>T, rs6265) and JARID2 (g.15281336G>A, rs9383046)] to elucidate their role in MDD onset.