title: A systematic review and meta-analysis of DNA methylation levels and imprinting disorders in children conceived by IVF/ICSI compared with children conceived spontaneously.
abstract: BACKGROUND
  Increasing numbers of children are being conceived by assisted reproductive technology (ART). A number of studies have highlighted an altered epigenetic status in gametes from infertile couples and the possibility of an increased risk of imprinting defects and somatic epigenetic changes in ART conceived children, but the results have been heterogeneous. We performed a systematic review of existing studies to compare the incidence of imprinting disorders and levels of DNA methylation in key imprinted genes in children conceived through in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) with those in children conceived spontaneously.
  
  
  METHODS
  A detailed search strategy was used to conduct electronic literature searches (spanning 1978 to 2013) on Medline, EMBASE, the Cochrane Library and Web of Science. Abstracts of relevant conference papers were identified. As randomized trials are not feasible in this context, we included observational (cohort and case-control) studies comparing outcomes in children conceived through ART with those conceived spontaneously, irrespective of the language of publication. The outcome measures were DNA methylation and the incidence of imprinting disorders.
  
  
  RESULTS
  A total of 351 publications were identified by the initial search. Of these, 26 were excluded as duplicates and 241 were excluded after reviewing the abstracts, then of those remaining 66 were excluded after review of the full text. A total of 18 papers were included in the review. Apart from one case-control study, all were cohort studies. There was a degree of clinical heterogeneity in terms of the study population, type of infertility treatment, and samples obtained from exposed and unexposed children. DNA methylation levels were either presented as categorical data (hypo-, hyper- or normally methylated DNA) or continuous data (i.e. percentage of methylated DNA). The combined odds ratio (95% confidence intervals) of any imprinting disorder in children conceived through ART was 3.67 (1.39, 9.74) in comparison with spontaneously conceived children. Meta-analysis of data from relevant studies revealed that the weighted mean difference (95% confidence intervals) in methylation percent between IVF/ICSI versus spontaneously conceived children were as follows: H19: -0.46(-1.41, 0.49), PEG1-MEST: 0.47 (-2.07, 3.01), GRB10: -0.05 (-0.43, 0.33), IGF2: -0.15 (-1.09, 0.79), SNRPN: -0.55 (-1.55, 0.46), KvDMR/KCNQ10T1: -0.16 (-0.34, 0.02) and PEG3: -0.24 (-1.72, 1.24).
  
  
  CONCLUSIONS
  There was an increase in imprinting disorders in children conceived though IVF and ICSI but insufficient evidence for an association between ART and methylation in other imprinted genes. Heterogeneity in the types of fertility treatment, the imprinted regions studied, the tissues used and the methods of measurement, reduce our ability to assess the full effect of ART on DNA methylation and imprinting. More controlled studies, using standardized methodologies, in larger, better clinically defined populations are needed.
authors: Division of Applied Health Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK.
authors: Gabija
authors: G
authors: Lazaraviciute
authors: Division of Applied Health Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK.
authors: Miriam
authors: M
authors: Kauser
authors: Division of Applied Health Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK.
authors: Sohinee
authors: S
authors: Bhattacharya
authors: Division of Lifelong Health, Rowett Institute of Nutrition and Health, University of Aberdeen, Greenburn Road, Bucksburn, Aberdeen AB21 9SB, UK.
authors: Paul
authors: P
authors: Haggarty
authors: Division of Applied Health Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK s.bhattacharya@abdn.ac.uk.
authors: Siladitya
authors: S
authors: Bhattacharya
mesh_terms: D002648:Child; D015331:Cohort Studies; D019175:DNA Methylation / Q000502:physiology*; D005307:Fertilization in Vitro / Q000009:adverse effects; D051383:GRB10 Adaptor Protein / Q000502:physiology; D018392:Genomic Imprinting / Q000502:physiology*; D006801:Humans; D007246:Infertility / Q000628:therapy; D024642:Potassium Channels, Voltage-Gated / Q000502:physiology; D011506:Proteins / Q000502:physiology; D062085:RNA, Long Noncoding / Q000502:physiology; D020554:Sperm Injections, Intracytoplasmic / Q000009:adverse effects; D055517:snRNP Core Proteins / Q000502:physiology
chemical_list: C094335:H19 long non-coding RNA; C485621:KCNQ1OT1 long non-coding RNA, human; D024642:Potassium Channels, Voltage-Gated; D011506:Proteins; D062085:RNA, Long Noncoding; C103637:mesoderm specific transcript protein; D055517:snRNP Core Proteins; D051383:GRB10 Adaptor Protein
keywords: DNA methylation; ICSI; IVF; epigenetic disorders; imprinting disorders