HUMAN MOLECULAR GENETICS: Genetic basis of schizophrenia & bipolar disorder.

From NEW SCIENTIST

Human Molecular Genetics

hmg.oxfordjournals.org

September 9, 2011

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

Emma L. Dempster1,†, Ruth Pidsley1,†, Leonard C. Schalkwyk1, Sheena Owens2, Anna Georgiades2, Fergus Kane2, Sridevi Kalidindi2, Marco Picchioni2,3, Eugenia Kravariti2, Timothea Toulopoulou2, Robin M. Murray2 and Jonathan Mill1,*

+ Author Affiliations

1MRC Social, Genetic and Developmental Psychiatry Centre and

2Department of Psychosis Studies, Institute of Psychiatry, King's College London, De Crespigny Park, Denmark Hill, London SE5 8AF, UK and

3St Andrew's Academic Centre, Northampton NN1 5BG, UK

↵*To whom correspondence should be addressed at: SGDP Centre, Institute of Psychiatry, King's College London, Denmark Hill, London SE5 8AF, UK. Tel: +44 2078480859; Fax: +44 2078480866; Email: jonathan.mill@kcl.ac.uk

↵† These authors contributed equally to this work.



Received July 12, 2011.

Accepted September 7, 2011.

Abstract

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.

© The Author 2011. Published by Oxford University Press.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.