The importance of epigenomic studies in schizophrenia

Male-specific association between dopamine receptor D4 gene methylation and schizophrenia

Objective

The goal of our study was to investigate whether DRD4 gene DNA methylation played an important role in the susceptibility of Han Chinese SCZ.

Methods

Using the bisulphite pyrosequencing technology, DNA methylation levels of 6 CpG dinucleotides in DRD4 CpG island were measured among 30 paranoid SCZ patients, 30 undifferentiated SCZ patients, and 30 age- and gender-matched healthy controls.

Results

Strong correlation was observed among the six CpG sites (r>0.5, P<0.01), thus average methylation levels were applied thereafter. Our results indicated that there was a significant association between DRD4 methylation and the risk of SCZ (P = 0.003), although there was no significant difference in DRD4 methylation between the two SCZ subtypes (P = 0.670). A breakdown analysis by gender showed that the significant association of DRD4 methylation and SCZ was driven by males (P<0.001) but not by females (P = 0.835). DRD4 methylation was significantly associated with p300 in male SCZ patients (r = −0.543, P = 0.005) but not in female SCZ patients (r = 0.110, P = 0.599). Moreover, receiver operating characteristic (ROC) curves showed DRD4 methylation was able to predict the status of SCZ in males [area under curve (AUC) = 0.832, P = 0.002] but not in females (AUC = 0.483, P = 0.876). Finally, a further expression experiment showed that DRD4 methylation in the gene body was positively associated with gene expression, although the exact mechanism of gene regulation remained unknown for this interesting DRD4 methylation.

Conclusion

The gender disparity in the DRD4 DNA methylation provides novel insights into the pathogenesis of SCZ.

A network medicine approach to psychiatric genetics

The major psychiatric disorders are complex in nature, meaning that they are influenced by multiple environmental and genetic exposures that perturb the intricate cellular network, resulting in disease. In general, psychiatric diseases are highly heritable but also have important environmental etiologies. Environmental influences include neonatal exposures, social environments, psychological mechanisms, and abnormal functioning of the neurotransmitter system. Molecular influences can be identified using many data types including genomics, epigenomics, transcriptomics, metabolomics, and proteomics. The emerging field of network medicine offers a new approach to explore the complexities of disease development in a framework that considers a holistic, rather than a reductionist viewpoint. In this review we explain a general framework of how the network medicine approach can provide valuable insight into understanding important molecular mechanisms that contribute to the pathogenesis of psychiatric disorders.

Detection of metabolic syndrome in schizophrenia and implications for antipsychotic therapy : is there a role for folate?

In general, the presence of metabolic syndrome is associated with significant cardiovascular mortality and represents a growing public health concern in the USA. Patients with schizophrenia have a three times greater risk of death than the general population, with cardiovascular disease being the most common cause of this mortality. Use of atypical antipsychotics (AAPs) to treat schizophrenia contributes significantly to this cardiovascular risk. While several different clinical guidelines currently exist to monitor the metabolic consequences of AAP use, implementation is lacking. Because of under-monitoring of side effects and the lack of alternative treatment choices in schizophrenia, research has focused on identification of various biomarkers and pharmacogenomic targets to focus on the patients at greatest risk of metabolic syndrome, thus aiming to increase the efficacy and minimize the side effects of AAPs. This has led to several different lines of research. This review focuses on summarizing the differing metabolic syndrome criteria, monitoring guidelines for use of AAPs, and the role of folic acid as it relates to metabolic syndrome within the schizophrenia population. It concentrates not only on the pharmacogenomics of folic acid metabolism but also on its epigenetic interaction with the environment. From this work, genetic variation within both the methylenetetrahydrofolate reductase (MTHFR) gene and the catechol-O-methyltransferase (COMT) gene has been associated with an increased risk of metabolic syndrome in schizophrenia patients treated with AAPs. Furthermore, work on the combination of folate pharmacogenetics and epigenetics has uncovered relationships between methylation, schizophrenia disease, treatment type, and metabolic syndrome. Despite several areas of biomarker research into schizophrenia-related metabolic syndrome, translation into the clinical setting is still lacking, and further studies are needed to bridge this gap. In the future, folate supplementation may prove to be an easy and effective clinical tool for prevention and/or treatment of metabolic syndrome associated with AAP treatment, but clearly more research needs to be done in this area.

Gender-dependent miR-375 promoter methylation and the risk of type 2 diabetes

Promoter DNA methylation may reflect the interaction between genetic background and environmental factors in the development of metabolic disorders, including type 2 diabetes (T2D). As an epigenetic factor of T2D, miR-375 plays an important role in the functional accommodation of islet cells. In the present study, we investigated the association of promoter DNA methylation of the miR-375 gene with the risk of T2D. Using bisulfite pyrosequencing technology, the DNA methylation levels of eight CpG dinucleotides on the miR-375 promoter were measured in 48 T2D cases and 48 healthy controls. The majority of CpGs (with the exception of CpG7) had significantly higher methylation levels in women compared with those in men (P<0.05). The methylation levels of the eight CpGs were significantly correlated with each other (P<0.001). No significant association between miR-375 gene promoter methylation and the risk of T2D was identified (P=0.417). Similar results were observed in the breakdown analysis by gender (men, P=0.844; women, P=0.234). In addition, although a correlation between the CpG8 methylation level of miR-375 and total triglyceride level was identified in women (P=0.009), DNA methylation of the majority of CpGs in the miR-375 gene promoter was not associated with the clinical metabolic features of the individuals.