DNA methylation differences in monozygotic twin pairs discordant for schizophrenia identifies psychosis related genes and networks.
BACKGROUND
Despite their singular origin, monozygotic twin pairs often display discordance for complex disorders including schizophrenia. It is a common (1%) and often familial disease with a discordance rate of ~50% in monozygotic twins. This high discordance is often explained by the role of yet unknown environmental, random, and epigenetic factors. The involvement of DNA methylation in this disease appears logical, but remains to be established.


METHODS
We have used blood DNA from two pairs of monozygotic twins discordant for schizophrenia and their parents in order to assess genome-wide methylation using a NimbleGen Methylation Promoter Microarray.


RESULTS
The genome-wide results show that differentially methylated regions (DMRs) exist between members representing discordant monozygotic twins. Some DMRs are shared with parent(s) and others appear to be de novo. We found twenty-seven genes affected by DMR changes that were shared in the affected member of two discordant monozygotic pairs from unrelated families. Interestingly, the genes affected by pair specific DMRs share specific networks. Specifically, this study has identified two networks; "cell death and survival" and a "cellular movement and immune cell trafficking". These two networks and the genes affected have been previously implicated in the aetiology of schizophrenia.


CONCLUSIONS
The results are compatible with the suggestion that DNA methylation may contribute to the discordance of monozygotic twins for schizophrenia. Also, this may be accomplished by the direct effect of gene specific methylation changes on specific biological networks rather than individual genes. It supports the extensive genetic, epigenetic and phenotypic heterogeneity implicated in schizophrenia.
Department of Biology, The University of Western Ontario, N6A 5B7, London, Ontario, Canada. ccastel3@uwo.ca.
Christina A
CA
Castellani
Department of Biology, The University of Western Ontario, N6A 5B7, London, Ontario, Canada. blaufer@uwo.ca.
Benjamin I
BI
Laufer
Department of Biology, The University of Western Ontario, N6A 5B7, London, Ontario, Canada. mmelka@uwo.ca.
Melkaye G
MG
Melka
Department of Biology, The University of Western Ontario, N6A 5B7, London, Ontario, Canada. ediehl@uwo.ca.
Eric J
EJ
Diehl
Department of Psychiatry, The University of Western Ontario, N6A 5B7, London, Ontario, Canada. roreilly@uwo.ca.
Richard L
RL
O'Reilly
Department of Biology, The University of Western Ontario, N6A 5B7, London, Ontario, Canada. ssingh@uwo.ca.|Department of Psychiatry, The University of Western Ontario, N6A 5B7, London, Ontario, Canada. ssingh@uwo.ca.
Shiva M
SM
Singh
D000328:Adult; D018899:CpG Islands; D019175:DNA Methylation; D004200:Diseases in Twins; D044127:Epigenesis, Genetic; D005260:Female; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D020022:Genetic Predisposition to Disease; D015894:Genome, Human; D006657:Histones / Q000737:chemistry; D006801:Humans; D008875:Middle Aged; D005810:Multigene Family; D010375:Pedigree; D010641:Phenotype; D011401:Promoter Regions, Genetic; D011618:Psychotic Disorders / Q000235:genetics*; D012559:Schizophrenia / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*
D006657:Histones