BDNF and major depressive disorder: Based on the literature data, in this study we are going to investigate the effects of single nucleotide polymorphisms of four genes in relation to blood plasma LPS and peripheral cytokines concentrations and clinical manifestation of MDD: Brain-derived neurotrophic factor (BDNF) rs6265 gene [55], Glycogen synthase kinase 3β (GSK3β) rs6438552 gene [56], MAPK1 rs6928, protein encoding gene [57], and synapsin 1 encoding gene -SYN1 [58].