DNA Methylation and copy number variation of the complement C4A and Cub and Sushi multiple domains 1 genes in Schizophrenia patients and healthy controls

Abstract

Schizophrenia is a chronic and disabling mental illness with unknown cause and incompletely understood pathogenesis. Evidence from genome-wide association studies (GWAS) and experimental studies had suggested the role of two immune related proteins, the complement C4, coded partly by the C4A gene, and the CUB and Sushi Multiple Domains 1 (CSMD1). However, there was no available report on the association between schizophrenia and DNA methylation of the C4A and CSMD1 genes. Such study is important because DNA methylation is a modifiable factor that can affect candidate genes’ expression and therefore explain the genetic-environment interaction in schizophrenia’s pathogenesis. Both genes also have copy number variation (CNV) which can influence gene expression. This study aims to compare the DNA methylation level and the copy number of C4A and CSMD1 genes between schizophrenia patients and healthy controls, and to evaluate their relationship with schizophrenia psychopathology. A total of 183 schizophrenia patients and 212 healthy controls were included in this comparative cross-sectional study. DNA methylation levels and gene copy number were determined from peripheral blood samples using MethyLightTM analysis and droplet digital polymerase chain reaction (ddPCR) respectively. C4 plasma levels was measured using immunoturbidimetry. Psychopathological data of patients were measured using the Positive and Negative Syndrome Scale (PANSS) and the Personal and Social Performance (PSP) scale. Plasma C4 levels were found to be significantly higher in schizophrenia patients compared to controls (p < 0.001). While C4A DNA methylation levels and copy number were both positively correlated with plasma C4 levels (p < 0.001), there was no significant difference in the two variables between patients and controls. The DNA methylation levels of CSMD1 were significantly lower in schizophrenia patients compared to healthy controls (p = 0.001), but its copy number did not differ significantly between the groups. C4A deletion and higher CSMD1 DNA methylation levels were also associated with lesser positive symptom severity (p = 0.027). In multivariate analysis, both CSMD1 DNA methylation levels and plasma C4 levels were significant predictors for schizophrenia. Overall, the results suggested the potential involvement of DNA methylation of C4A and CSMD1 in schizophrenia pathophysiology, particularly in pathways relevant to the positive symptoms. Since DNA methylation may be reversed, this could be a useful target in for the development of new treatment in the future. Further studies are required to identify the underlying mechanism for these findings.