title: Disease-associated epigenetic changes in monozygotic twins discordant for schizophrenia and bipolar disorder.
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.
authors: MRC Social, Genetic and Developmental Psychiatry Centre, King’s College London, De Crespigny Park, Denmark Hill, London SE5 8AF, UK.
authors: Emma L
authors: EL
authors: Dempster
authors: Ruth
authors: R
authors: Pidsley
authors: Leonard C
authors: LC
authors: Schalkwyk
authors: Sheena
authors: S
authors: Owens
authors: Anna
authors: A
authors: Georgiades
authors: Fergus
authors: F
authors: Kane
authors: Sridevi
authors: S
authors: Kalidindi
authors: Marco
authors: M
authors: Picchioni
authors: Eugenia
authors: E
authors: Kravariti
authors: Timothea
authors: T
authors: Toulopoulou
authors: Robin M
authors: RM
authors: Murray
authors: Jonathan
authors: J
authors: Mill
mesh_terms: D001714:Bipolar Disorder / Q000235:genetics*; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation / Q000235:genetics; D003710:Demography; D044127:Epigenesis, Genetic; D005260:Female; D053263:Gene Regulatory Networks / Q000235:genetics; D020022:Genetic Predisposition to Disease; D015894:Genome, Human / Q000235:genetics; D006801:Humans; D008297:Male; D011401:Promoter Regions, Genetic; D015203:Reproducibility of Results; D012559:Schizophrenia / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*; D055815:Young Adult