Objectives Schizophrenia is a neuropsychiatric disease caused by disorders in brain development due to genetic and environmental factors. The interactions and mechanisms of the two main etiological factors are not fully understood despite neurobiological, clinical and genetic research and more research is needed. In this study, we aimed to investigate the DNA methylation differences in the matrix metalloproteinase 9 gene (MMP9) between schizophrenia and healthy control groups. Methods Our study investigates DNA methylation patterns in the MMP9 gene in peripheral blood cells of schizophrenia patients. For this purpose, pyrosequencing method was used to analyze DNA methylation status of C-phosphate-G (CpG) regions in the 7th exon of MMP9 in 40 schizophrenia patients and 32 healthy individuals who admitted to our university hospital’s psychiatry clinic. Results In our results, it has been shown that there is a difference between MMP9 gene DNA methylations between healthy individuals and schizophrenia patients. Significant differences were found in the MMP9 gene exon 7 region in CpG 7-3, CpG 7-4, CpG 7-5 positions and mean methylation patterns between these two groups. Conclusions This study provided evidence that DNA methylation differences may exist between schizophrenia patients and healthy individuals, and emphasized the epigenetic aspect of the disorder.

Schizophrenia is a mental disorder characterized by delusions, hallucinations and various behavioral disorders. Affecting approximately 1% of the world's population, schizophrenia not only affects patients, but also other members of the society. Genetic and environmental factors play roles in the etiology of the disorder.Genetics, neurodevelopmental disorder, drug use, urban life, alone or together can be counted as the factors that cause the disorder. Despite increasing studies in recent years, the factors causing the formation of schizophrenia have not been fully clarified and more research is needed. Although genetic factors are risk factors for schizophrenia, it is thought that some environmental factors affect the emergence of the disorder. Epigenetic mechanisms regulate gene functions without changing the nucleotide sequence of DNA. DNA methylation is associated with schizophrenia, and methylation status studies have been conducted in many schizophrenia candidate genes. Examination of DNA methylation states will contribute significantly to psychiatric research.In this review, data published in global databases obtained from DNA methylation studies related with schizophrenia are summarized and their importance in schizophrenia is briefly discussed.