Alterations of miRNA expression has been reported in studies on post-mortem brain tissue of schizophrenia patient, and upregulation of miR-328, miR-17-5p, miR-134, miR-652, miR-382, and miR-107 has been detected (Perkins et al., 2007; Santarelli et al., 2011). Analysis on brain tissue has further revealed that expression of miR-130b is located in the locus susceptible for schizophrenia (Burmistrova et al., 2007). I

hypomethylations have also been detected in other genes, such as AluY A3 CpG (Li et al., 2019), promoter of GRIN2B (Fachim et al., 2019), CpG2 and CpG3 in TREM2 intron 1 (Yoshino et al., 2017), CpG sites in FAM63B and intergenic region on chromosome 16, CpG sites in TBC1D22A (Sugawara et al., 2018), and COMT (Nour El Huda et al., 2018) in schizophrenia compared with controls. Additionally, methylation of COMT was lower in atypical antipsychotics group compared to typical antipsychotics group

The non-coding RNAs (ncRNAs) are unique RNA transcripts that have been widely identified in eukaryotic genomes and play critical parts in the occurrence and development of many diseases.

In contrast, DNA hypomethylation has also been identified in brain tissue and peripheral blood of schizophrenia patients. For instance, the hypomethylation of promoter region of catechol-O-methyltransferase (COMT), the gene from dopaminergic pathway, has been revealed in frontal lobe in schizophrenia (Abdolmaleky et al., 2006)

Mental disorders are complex, multifactorial diseases involving chronic changes in the structure and function of neural circuits. Schizophrenia and several other mental disorders are highly hereditary (Burmeister et al., 2008), while epigenetic disorders are caused by environmental factors such as certain life experiences and stress.

If the DNA regulatory sequences contain a large amount of 5-methylcytosine, it can block the binding of transcription factors to DNA, thus affecting gene transcription.

Both genetic and environmental factors are considered as important contributors to the development and progression of this disorder. The environmental factors have been linked to changes in gene expression through epigenetic modulations,

Some schizophrenia- and autism-associated genes, such as DLG4 (disks large homolog 4, MIM 602887), DRD2 (dopamine receptor D2, MIM 126450), NOS1 (nitric oxide synthase 1, MIM 163731), NRXN1 (neurexin-1, MIM 600565), and SOX10 (sex-determining region Y-box 10, MIM 602229), have all been shown to have age-related dynamically methylated changes throughout the entire lifetime, especially in the fetal and postnatal stages