Journal Article

Disease-associated epigenetic changes in monozygotic twins discordant for schizophrenia and bipolar disorder

Emma L. Dempster, Ruth Pidsley, Leonard C. Schalkwyk, Sheena Owens, Anna Georgiades, Fergus Kane, Sridevi Kalidindi, Marco Picchioni, Eugenia Kravariti, Timothea Toulopoulou, Robin M. Murray and Jonathan Mill

in Human Molecular Genetics

Volume 20, issue 24, pages 4786-4796
Published in print December 2011 | ISSN: 0964-6906
Published online September 2011 | e-ISSN: 1460-2083 | DOI: https://dx.doi.org/10.1093/hmg/ddr416

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Studies of the major psychoses, schizophrenia (SZ) and bipolar disorder (BD), have traditionally focused on genetic and environmental risk factors, although more recent work has highlighted an additional role for epigenetic processes in mediating susceptibility. Since monozygotic (MZ) twins share a common DNA sequence, their study represents an ideal design for investigating the contribution of epigenetic factors to disease etiology. We performed a genome-wide analysis of DNA methylation on peripheral blood DNA samples obtained from a unique sample of MZ twin pairs discordant for major psychosis. Numerous loci demonstrated disease-associated DNA methylation differences between twins discordant for SZ and BD individually, and together as a combined major psychosis group. Pathway analysis of our top loci highlighted a significant enrichment of epigenetic changes in biological networks and pathways directly relevant to psychiatric disorder and neurodevelopment. The top psychosis-associated, differentially methylated region, significantly hypomethylated in affected twins, was located in the promoter of ST6GALNAC1 overlapping a previously reported rare genomic duplication observed in SZ. The mean DNA methylation difference at this locus was 6%, but there was considerable heterogeneity between families, with some twin pairs showing a 20% difference in methylation. We subsequently assessed this region in an independent sample of postmortem brain tissue from affected individuals and controls, finding marked hypomethylation (>25%) in a subset of psychosis patients. Overall, our data provide further evidence to support a role for DNA methylation differences in mediating phenotypic differences between MZ twins and in the etiology of both SZ and BD.

Journal Article.  6968 words.  Illustrated.

Subjects: Genetics and Genomics

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