An investigation of the involvement of methylation in the parhogenesis of mental diseases by differential genomic analyses of monozygotic twins discordant for the diseases.

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(1) Methylation and schizophreniaTotal me ethylated cytosine volumes in leucocytes were measured using HPLC and compared between patients with schizophrenia and age and sex matched normal controls. Leucocytes from male patients with schizophrenia contained significantly less total me ethylated cytosine than those from normal controls. The difference was observed especially in the young patients (<35 years old). There was no significant difference for female patients. Two Human endogenous retrovirus (HERV) that retain the transcriptional activity which is inhibited by methylation were located on chromosome 1q21-q22 and 22q12 which were susceptible loci repeatedly observed in the linkage study of schizophrenia. These suggest the involvement of methylation in the pathogenesis of schizophrenia(2) Differential genomic scans of discordant monozygotic twinsFluorescent representational genomic profiling (FRGP) was applied to DNAs from monozygotic twins discordant for schizophrenia, bipolar disorder, autism and narcolepsy. Discordant spots containing discordant DNA fragments between affected and non-affected twins from the monozygotic twins from autism, schizophrenia and bipolar disorder. Two candidate genes (4p14, 12q24.11) for autism, 1gnee (6q13) and 1 gene (7q31) were implicated by the direct cloning of the spots. Furthermore, the difference of an autism gene was revealed due to its different methylation status in the promoter region.(3) The discovery of bipolar disorder susceptibility gene, XBP1DNA Microarray analysis of lymphoblasted cells from two monozygotic twins discordant for bipolar disorder revealed lower expression of XBP1 and GRP78 genes that involved in the lowered endoplasmic reticulum (ER) stress. A polymorphism (-116 G/C) in the promoter region of XBP1 was responsible for lowered expression. The involvement of methylation in the expression of XBP1 is a next focus