title: Storage conditions and stability of global DNA methylation in placental tissue.
abstract: OBJECTIVE
  The placenta is an informative and easily available tissue for many epidemiological studies. We analyzed the extent to which storage delay affects DNA methylation.
  
  
  METHODS
  Biopsies from two placentas were sequentially stored at -80°C after standing at room temperature for 30 min, 1 h, 2 h, 6 h and 24 h. Global DNA methylation was measured by bisulfite pyrosequencing of repetitive elements and the luminometric methylation assay.
  
  
  RESULTS
  Small changes in global DNA methylation in relation to time-to-storage were observed by pyrosequencing, with a coefficient of variation (COV) of 2.49% (placenta 1) and 2.86% (placenta 2), similar to the mean technical variation observed for pyrosequencing (COV: 1.91 and 1.51%, respectively). A luminometric methylation assay yielded more variable results in the two placentas analyzed, both among time points (COV: 9.13 and 10.35%, respectively) and technical replicates (COV: 11.60 and 9.80%, respectively).
  
  
  CONCLUSIONS
  Global DNA methylation is stable at room temperature. However, some techniques to measure methylation might be confounded by DNA degradation caused by a delay in storage.
authors.affiliation: Center for Research in Environmental Epidemiology CREAL, Barcelona, Catalonia, Spain. nvilahur@creal.cat
authors.forename: Nadia
authors.initials: N
authors.lastname: Vilahur
authors.forename: Andrea A
authors.initials: AA
authors.lastname: Baccarelli
authors.forename: Mariona
authors.initials: M
authors.lastname: Bustamante
authors.forename: Silvia
authors.initials: S
authors.lastname: Agramunt
authors.forename: Hyang-Min
authors.initials: HM
authors.lastname: Byun
authors.forename: Mariana F
authors.initials: MF
authors.lastname: Fernandez
authors.forename: Jordi
authors.initials: J
authors.lastname: Sunyer
authors.forename: Xavier
authors.initials: X
authors.lastname: Estivill
mesh_terms: D004247:DNA / Q000378:metabolism*; D019175:DNA Methylation; D005260:Female; D006801:Humans; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D017422:Sequence Analysis, DNA; D013696:Temperature; D013997:Time Factors
chemical_list: D004247:DNA