title: Adult monozygotic twins discordant for intra-uterine growth have indistinguishable genome-wide DNA methylation profiles.
abstract: BACKGROUND
  Low birth weight is associated with an increased adult metabolic disease risk. It is widely discussed that poor intra-uterine conditions could induce long-lasting epigenetic modifications, leading to systemic changes in regulation of metabolic genes. To address this, we acquire genome-wide DNA methylation profiles from saliva DNA in a unique cohort of 17 monozygotic monochorionic female twins very discordant for birth weight. We examine if adverse prenatal growth conditions experienced by the smaller co-twins lead to long-lasting DNA methylation changes.
  
  
  RESULTS
  Overall, co-twins show very similar genome-wide DNA methylation profiles. Since observed differences are almost exclusively caused by variable cellular composition, an original marker-based adjustment strategy was developed to eliminate such variation at affected CpGs. Among adjusted and unchanged CpGs 3,153 are differentially methylated between the heavy and light co-twins at nominal significance, of which 45 show sensible absolute mean β-value differences. Deep bisulfite sequencing of eight such loci reveals that differences remain in the range of technical variation, arguing against a reproducible biological effect. Analysis of methylation in repetitive elements using methylation-dependent primer extension assays also indicates no significant intra-pair differences.
  
  
  CONCLUSIONS
  Severe intra-uterine growth differences observed within these monozygotic twins are not associated with long-lasting DNA methylation differences in cells composing saliva, detectable with up-to-date technologies. Additionally, our results indicate that uneven cell type composition can lead to spurious results and should be addressed in epigenomic studies.
authors.forename: Nicole Y P
authors.initials: NY
authors.lastname: Souren
authors.forename: Pavlo
authors.initials: P
authors.lastname: Lutsik
authors.forename: Gilles
authors.initials: G
authors.lastname: Gasparoni
authors.forename: Sascha
authors.initials: S
authors.lastname: Tierling
authors.forename: Jasmin
authors.initials: J
authors.lastname: Gries
authors.forename: Matthias
authors.initials: M
authors.lastname: Riemenschneider
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Fryns
authors.forename: Catherine
authors.initials: C
authors.lastname: Derom
authors.forename: Maurice P
authors.initials: MP
authors.lastname: Zeegers
authors.forename: Jörn
authors.initials: J
authors.lastname: Walter
mesh_terms: D000328:Adult; D001724:Birth Weight; D019175:DNA Methylation; D005260:Female; D015894:Genome, Human; D059014:High-Throughput Nucleotide Sequencing / Q000379:methods*; D006801:Humans; D008875:Middle Aged; D008969:Molecular Sequence Data; D012463:Saliva / Q000166:cytology; D017422:Sequence Analysis, DNA; D014430:Twins, Monozygotic / Q000235:genetics*; D055815:Young Adult