title: Genome-wide placental DNA methylation analysis of severely growth-discordant monochorionic twins reveals novel epigenetic targets for intrauterine growth restriction.
abstract: BACKGROUND
  Intrauterine growth restriction (IUGR), which refers to reduced fetal growth in the context of placental insufficiency, is etiologically heterogeneous. IUGR is associated not only with perinatal morbidity and mortality but also with adult-onset disorders, such as cardiovascular disease and diabetes, posing a major health burden. Placental epigenetic dysregulation has been proposed as one mechanism that causes IUGR; however, the spectrum of epigenetic pathophysiological mechanisms leading to IUGR remains to be elucidated. Monozygotic monochorionic twins are particularly affected by IUGR, in the setting of severe discordant growth. Because monozygotic twins have the same genotype at conception and a shared maternal environment, they provide an ideal model system for studying epigenetic dysregulation of the placenta.
  
  
  RESULTS
  We compared genome-wide placental DNA methylation patterns of severely growth-discordant twins to identify novel candidate genes for IUGR. Snap-frozen placental samples for eight severely growth-discordant monozygotic monochorionic twin pairs were obtained at delivery from each twin. A high-resolution DNA methylation array platform was used to identify methylation differences between IUGR and normal twins. Our analysis revealed differentially methylated regions in the promoters of eight genes: DECR1, ZNF300, DNAJA4, CCL28, LEPR, HSPA1A/L, GSTO1, and GNE. The largest methylation differences between the two groups were in the promoters of DECR1 and ZNF300. The significance of these group differences was independently validated by bisulfite pyrosequencing, implicating aberrations in fatty acid beta oxidation and transcriptional regulation, respectively. Further analysis of the array data identified methylation changes most prominently affecting the Wnt and cadherin pathways in the IUGR cohort.
  
  
  CONCLUSIONS
  Our results suggest that IUGR in monozygotic twins is associated with impairments in lipid metabolism and transcriptional regulation as well as cadherin and Wnt signaling. We show that monozygotic monochorionic twins discordant for growth provide a useful model to study one type of the epigenetic placental dysregulation that drives IUGR.
authors.affiliation: Division of Clinical and Metabolic Genetics, The Hospital for Sick Children, Toronto, Ontario Canada ; Department of Paediatrics, University of Toronto, Toronto, Ontario Canada ; Genetics and Genome Biology Program, The Hospital for Sick Children, Toronto, Ontario Canada ; The Prenatal and Medical Genetics Program, Department of Obstetrics and Gynaecology, Mount Sinai Hospital, Toronto, Ontario Canada.
authors.forename: Maian
authors.initials: M
authors.lastname: Roifman
authors.affiliation: Genetics and Genome Biology Program, The Hospital for Sick Children, Toronto, Ontario Canada.
authors.forename: Sanaa
authors.initials: S
authors.lastname: Choufani
authors.affiliation: Genetics and Genome Biology Program, The Hospital for Sick Children, Toronto, Ontario Canada ; Centre for Computational Medicine, The Hospital for Sick Children, Toronto, Ontario Canada.
authors.forename: Andrei L
authors.initials: AL
authors.lastname: Turinsky
authors.affiliation: C.S. Mott Center for Human Growth and Development, Wayne State School of Medicine, Wayne State University, Detroit, MI USA.
authors.forename: Sascha
authors.initials: S
authors.lastname: Drewlo
authors.affiliation: Maternal-Fetal Medicine Division, Department of Obstetrics and Gynecology, Mount Sinai Hospital, Toronto, Ontario Canada ; Department of Laboratory Medicine and Pathology, University of Toronto, Toronto, Ontario Canada.
authors.forename: Sarah
authors.initials: S
authors.lastname: Keating
authors.affiliation: Genetics and Genome Biology Program, The Hospital for Sick Children, Toronto, Ontario Canada ; Centre for Computational Medicine, The Hospital for Sick Children, Toronto, Ontario Canada ; Department of Computer Science, University of Toronto, Toronto, Ontario Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Brudno
authors.affiliation: Department of Laboratory Medicine and Pathology, University of Toronto, Toronto, Ontario Canada ; Department of Obstetrics and Gynecology, University of Toronto, Toronto, Ontario Canada.
authors.forename: John
authors.initials: J
authors.lastname: Kingdom
authors.affiliation: Division of Clinical and Metabolic Genetics, The Hospital for Sick Children, Toronto, Ontario Canada ; Department of Paediatrics, University of Toronto, Toronto, Ontario Canada ; Genetics and Genome Biology Program, The Hospital for Sick Children, Toronto, Ontario Canada ; Institute of Medical Science, University of Toronto, Toronto, Ontario Canada.
authors.forename: Rosanna
authors.initials: R
authors.lastname: Weksberg
mesh_terms: D019175:DNA Methylation; D004200:Diseases in Twins / Q000235:genetics*; D044127:Epigenesis, Genetic; D005260:Female; D005317:Fetal Growth Retardation / Q000235:genetics*; D005786:Gene Expression Regulation; D055106:Genome-Wide Association Study / Q000379:methods*; D006801:Humans; D008297:Male; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011401:Promoter Regions, Genetic; D014430:Twins, Monozygotic / Q000235:genetics*
keywords: Cadherin pathway; DECR1; DNA methylation; Intrauterine growth restriction; LEPR; Monochorionic twins; Monozygotic twins; Wnt pathway; ZNF300