title: Epigenetic signature of birth weight discordance in adult twins.
abstract: BACKGROUND
  A low birth weight has been extensively related to poor adult health outcomes. Birth weight can be seen as a proxy for environmental conditions during prenatal development. Identical twin pairs discordant for birth weight provide an extraordinary model for investigating the association between birth weight and adult life health while controlling for not only genetics but also postnatal rearing environment. We performed an epigenome-wide profiling on blood samples from 150 pairs of adult monozygotic twins discordant for birth weight to look for molecular evidence of epigenetic signatures in association with birth weight discordance.
  
  
  RESULTS
  Our association analysis revealed no CpG site with genome-wide statistical significance (FDR < 0.05) for either qualitative (larger or smaller) or quantitative discordance in birth weight. Even with selected samples of extremely birth weight discordant twin pairs, no significant site was found except for 3 CpGs that displayed age-dependent intra-pair differential methylation with FDRs 0.014 (cg26856578, p = 3.42e-08), 0.0256 (cg15122603, p = 1.25e-07) and 0.0258 (cg16636641, p = 2.05e-07). Among the three sites, intra-pair differential methylation increased with age for cg26856578 but decreased with age for cg15122603 and cg16636641. There was no genome-wide statistical significance for sex-dependent effects on intra-pair differential methylation in either the whole samples or the extremely discordant twins.
  
  
  CONCLUSIONS
  Genome-wide DNA methylation profiling did not reveal epigenetic signatures of birth weight discordance although some sites displayed age-dependent intra-pair differential methylation in the extremely discordant twin pairs.
authors.affiliation: Epidemiology, Biostatistics and Biodemography, Institute of Public Health, University of Southern Denmark, J, B, Winsløws Vej 9B, DK-5000 Odense C, Denmark. qtan@health.sdu.dk.
authors.forename: Qihua
authors.initials: Q
authors.lastname: Tan
authors.forename: Morten
authors.initials: M
authors.lastname: Frost
authors.forename: Bastiaan T
authors.initials: BT
authors.lastname: Heijmans
authors.forename: Jacob
authors.initials: J
authors.lastname: von Bornemann Hjelmborg
authors.forename: Elmar W
authors.initials: EW
authors.lastname: Tobi
authors.forename: Kaare
authors.initials: K
authors.lastname: Christensen
authors.forename: Lene
authors.initials: L
authors.lastname: Christiansen
mesh_terms: D000328:Adult; D000368:Aged; D001724:Birth Weight / Q000235:genetics*; D018899:CpG Islands; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D057890:Epigenomics; D005260:Female; D005865:Gestational Age; D006801:Humans; D008297:Male; D008875:Middle Aged; D014430:Twins, Monozygotic / Q000235:genetics*