title: Genome-wide methylomic analysis of monozygotic twins discordant for adolescent depression.
abstract: BACKGROUND
  Adolescent depression is a common neuropsychiatric disorder that often continues into adulthood and is associated with a wide range of poor outcomes including suicide. Although numerous studies have looked at genetic markers associated with depression, the role of epigenetic variation remains relatively unexplored.
  
  
  METHODS
  Monozygotic (MZ) twins were selected from an adolescent twin study designed to investigate the interplay of genetic and environmental factors in the development of emotional and behavioral difficulties. There were 18 pairs of MZ twins identified in which one member scored consistently higher (group mean within the clinically significant range) on self-rated depression than the other. We assessed genome-wide patterns of DNA methylation in twin buccal cell DNA using the Infinium HumanMethylation450 BeadChip from Illumina. Quality control and data preprocessing was undertaken using the wateRmelon package. Differentially methylated probes (DMPs) were identified using an analysis strategy taking into account both the significance and the magnitude of DNA methylation differences. The top differentially methylated DMP was successfully validated by bisulfite-pyrosequencing, and identified DMPs were tested in postmortem brain samples obtained from patients with major depressive disorder (n = 14) and matched control subjects (n = 15).
  
  
  RESULTS
  Two reproducible depression-associated DMPs were identified, including the top-ranked DMP that was located within STK32C, which encodes a serine/threonine kinase, of unknown function.
  
  
  CONCLUSIONS
  Our data indicate that DNA methylation differences are apparent in MZ twins discordant for adolescent depression and that some of the disease-associated variation observed in buccal cell DNA is mirrored in adult brain tissue obtained from individuals with clinical depression.
authors.affiliation: University of Exeter Medical School, Exeter University, Exeter. Electronic address: e.l.dempster@exeter.ac.uk.
authors.forename: Emma L
authors.initials: EL
authors.lastname: Dempster
authors.affiliation: Social Genetic Developmental Psychiatry Centre, Institute of Psychiatry, King's College London.
authors.forename: Chloe C Y
authors.initials: CC
authors.lastname: Wong
authors.affiliation: Social Genetic Developmental Psychiatry Centre, Institute of Psychiatry, King's College London.
authors.forename: Kathryn J
authors.initials: KJ
authors.lastname: Lester
authors.affiliation: University of Exeter Medical School, Exeter University, Exeter.
authors.forename: Joe
authors.initials: J
authors.lastname: Burrage
authors.affiliation: Department of Psychology, Goldsmiths, University of London, London, United Kingdom.
authors.forename: Alice M
authors.initials: AM
authors.lastname: Gregory
authors.affiliation: University of Exeter Medical School, Exeter University, Exeter; Social Genetic Developmental Psychiatry Centre, Institute of Psychiatry, King's College London.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Mill
authors.affiliation: Social Genetic Developmental Psychiatry Centre, Institute of Psychiatry, King's College London.
authors.forename: Thalia C
authors.initials: TC
authors.lastname: Eley
mesh_terms: D000293:Adolescent; D002531:Cerebellum / Q000378:metabolism / Q000473:pathology; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation / Q000235:genetics*; D003863:Depression / Q000235:genetics* / Q000473:pathology; D005260:Female; D016678:Genome / Q000235:genetics; D015894:Genome, Human; D006801:Humans; D008297:Male; D011180:Postmortem Changes; D011795:Surveys and Questionnaires; D014430:Twins, Monozygotic / Q000235:genetics*
keywords: Adolescent depression; DNA methylation; depression; epigenetic; genomics; monozygotic twins