title: 11p15 DNA-methylation analysis in monozygotic twins with discordant intrauterine development due to severe twin-to-twin transfusion syndrome.
abstract: BACKGROUND
  Prenatal growth restriction and low birth weight have been linked to long-term alterations of health, presumably via adaptive modifications of the epigenome. Recent studies indicate a plasticity of the 11p15 epigenotype in response to environmental changes during early stages of human development.
  
  
  METHODS
  We analyzed methylation levels at different 11p15 loci in 20 growth-discordant monozygotic twin pairs. Intrauterine development was discordant due to severe twin-to-twin transfusion syndrome (TTTS), which was treated by fetoscopic laser coagulation of communicating vessels before 25 weeks of gestation. Methylation levels at age 4 were determined in blood and buccal cell-derived DNA by the single nucleotide primer extension reaction ion pair reverse-phase high performance liquid chromatography (SNuPE IP RP HPLC) assay. Methylation at LINE-1 repeats was analyzed as an estimate of global methylation.
  
  
  RESULTS
  In general, variance of locus-specific methylation levels appeared to be higher in buccal cell- as compared to blood cell-derived DNA samples. Paired analyses within the twin pairs revealed significant differences at only one CpG site (IGF2 dmr0 SN3 (blood), +1.9% in donors; P = 0.013). When plotting the twin pair-discordance in birth weight against the degree of discordance in site-specific methylation at age 4, only a few CpGs were found to interact (one CpG site each at IGF2dmr0 in blood/saliva DNA, one CpG at LINE-1 repeats in saliva DNA), with 26 to 36% of the intra-twin pair divergence at these sites explained by prenatal growth discordance. However, across the entire cohort of 40 children, site-specific methylation did not correlate with SD-scores for weight or length at birth. Insulin-like growth factor-II serum concentrations showed significant within-twin pair correlations at birth (R = 0.57) and at age 4 (R = 0.79), but did not differ between donors and recipients. They also did not correlate with the analyzed 11p15 methylation parameters.
  
  
  CONCLUSIONS
  In a cohort of 20 growth-discordant monozygotic twin pairs, severe alteration in placental blood supply due to TTTS appears to leave only weak, if any, epigenetic marks at the analyzed CpG sites at 11p15.
authors.affiliation: Pediatric Endocrinology Division, Children's Hospital, University of Bonn, Adenauerallee 119, 53113 Bonn, Germany. felix.schreiner@ukb.uni-bonn.del.
authors.forename: Felix
authors.initials: F
authors.lastname: Schreiner
authors.forename: Bettina
authors.initials: B
authors.lastname: Gohlke
authors.forename: Sonja
authors.initials: S
authors.lastname: Stutte
authors.forename: Peter
authors.initials: P
authors.lastname: Bartmann
authors.forename: Kurt
authors.initials: K
authors.lastname: Hecher
authors.forename: Johannes
authors.initials: J
authors.lastname: Oldenburg
authors.forename: Osman
authors.initials: O
authors.lastname: El-Maarri
authors.forename: Joachim
authors.initials: J
authors.lastname: Woelfle