Through analyzing the expression levels of BDNF mRNA, acH3K9 and HDAC2, and the DNA methylation level of BDNF promoter I at relative CpG sites in hippocampus, we identified that DNA methylation and histone modifications of BDNF in the hippocampus were involved in the pathological process of depression (Figures 4H,I). The gene discussed is HDAC2; the disease is depressive disorder.