title: Differentially Methylated DNA Regions in Monozygotic Twin Pairs Discordant for Rheumatoid Arthritis: An Epigenome-Wide Study.
abstract: OBJECTIVE
  In an explorative epigenome-wide association study (EWAS) to search for gene independent, differentially methylated DNA positions and regions (DMRs) associated with rheumatoid arthritis (RA) by studying monozygotic (MZ) twin pairs discordant for RA.
  
  
  METHODS
  Genomic DNA was isolated from whole blood samples from 28 MZ twin pairs discordant for RA. DNA methylation was measured using the HumanMethylation450 BeadChips. Smoking, anti-cyclic citrullinated peptide antibodies, and immunosuppressive treatment were included as covariates. Pathway analysis was performed using GREAT.
  
  
  RESULTS
  Smoking was significantly associated with hypomethylation of a DMR overlapping the promoter region of theRNF5and theAGPAT1, which are implicated in inflammation and autoimmunity, whereas DMARD treatment induced hypermethylation of the same region. Additionally, the promotor region of bothS100A6andEFCAB4Bwere hypomethylated, and both genes have previously been associated with RA. We replicated several candidate genes identified in a previous EWAS in treatment-naïve RA singletons. Gene-set analysis indicated the involvement of immunologic signatures and cancer-related pathways in RA.
  
  
  CONCLUSIONS
  We identified several differentially methylated regions associated with RA, which may represent environmental effects or consequences of the disease and plausible biological pathways pertinent to the pathogenesis of RA.
authors.affiliation: The Danish Twin Registry, Epidemiology, Institute of Public Health, University of Southern Denmark , Odense , Denmark.
authors.forename: Anders J
authors.initials: AJ
authors.lastname: Svendsen
authors.affiliation: Department of Medical Genetics, Oslo University Hospital, University of Oslo , Oslo , Norway.
authors.forename: Kristina
authors.initials: K
authors.lastname: Gervin
authors.affiliation: Department of Medical Genetics, Oslo University Hospital, University of Oslo , Oslo , Norway.
authors.forename: Robert
authors.initials: R
authors.lastname: Lyle
authors.affiliation: The Danish Twin Registry, Epidemiology, Institute of Public Health, University of Southern Denmark , Odense , Denmark.
authors.forename: Lene
authors.initials: L
authors.lastname: Christiansen
authors.affiliation: Denmark and Odense Patient data Explorative Network (OPEN), Institute of Clinical Research, Odense University Hospital, University of Southern Denmark , Odense , Denmark.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Kyvik
authors.affiliation: Department of Rheumatology, Odense University Hospital, University of Southern Denmark , Odense , Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Junker
authors.affiliation: Department of Clinical Immunology, Odense University Hospital , Odense , Denmark.
authors.forename: Christian
authors.initials: C
authors.lastname: Nielsen
authors.affiliation: Department of Clinical Biochemistry and Immunology, Statens Serum Institute , Copenhagen , Denmark.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Houen
authors.affiliation: The Danish Twin Registry, Epidemiology, Institute of Public Health, University of Southern Denmark, Odense, Denmark; Unit of Human Genetics, Department of Clinical Research, University of Southern Denmark, Odense, Denmark.
authors.forename: Qihua
authors.initials: Q
authors.lastname: Tan
keywords: DNA methylation; epigenome-wide association study; monozygotic twins; pathway analysis; rheumatoid arthritis