SLC6A4 and major depressive disorder: • Hypermethylation at BDNF locus • CpG methylation in exon 1 biomarker for depressed patients • Patients may not respond to antidepressants• Antidepressants phosphorylate MeCP2 causing it to disassociate from methylated DNA•SLC6A4 methylation may be related to depression heritability• Environmental stressors disrupt methylation • Child-hood stressors associated with increased methylation at exon 1F of NR3C1• Early life adversity changes methylation of CpG sites in FKBP5• Pcdh genes show reduced promoter methylation in response to good maternal care