Gene Promoter DNA Methylations and Their Relationships With Endophenotypes in Patients With Schizophrenia

Schizophrenia is a disabling mental disease affecting about 1% of the worldwide population. There is an overall heritability estimate of 68% for the underlying liability to schizophrenia. Molecular epigenetic studies can overcome the complexities of traditional genetic studies and provide a new framework for the search of etiological factors in schizophrenia.

DNA methylation provides an example of an epigenetic process that affects gene expression. Several postmortem experiments have found that increased DNA methylation at the glutamic acid decarboxylase (GAD67) and reelin promoter, and hypomethylation of membrane-bound catechol-O-methyltransferase (MB-COMT) promoter gene in prefrontal cortex of schizophrenia patients.

Because it is impossible to obtain brain tissue from schizophrenia patients clinically, the peripheral blood mononuclear cell (PBMC) can partly represent the brain gene expression. It has been reported to use PBMC as biomarkers for epigenetic abnormalities, such as histone acetylation and methylation, in schizophrenia. To the investigators best knowledge, gene promoter DNA methylation abnormalities in schizophrenia have been limited to postmortem study. It warrants to studying the DNA methylation using schizophrenia's PBMC.

Recently, endophenotype strategy has emerged as an important tool in understanding the genetic architecture of schizophrenia. Some cognitive functions, such as attention and working memory (WM), have been used as candidate endophenotypes for genetic studies in schizophrenia. Synchronized GABA neurotransmission in the dorsolateral prefrontal cortex is required for adequate attention and working memory, suggesting that impairments in GABA-mediated inhibition in the prefrontal cortex could contribute to the endophenotype presentations in schizophrenia.