title: Origin of amnion and implications for evaluation of the fetal genotype in cases of mosaicism.
abstract: OBJECTIVE
  To investigate presence of trisomy in amniotic epithelium (uncultured amnion) and mesenchyme (cultured amnion) from mosaic cases to understand the origins of these tissues and their relationship to pregnancy outcome.
  
  
  METHODS
  Polymerase chain reaction (PCR) of microsatellite loci was used to determine the presence of trisomy (of meiotic origin only) in amnion samples from 33 placentas previously ascertained because of a prenatal diagnosis of trisomy mosaicism that was predominantly confined to the placental tissues.
  
  
  RESULTS
  In 16 (48%) of 33 cases, trisomy was confirmed to be present by molecular analysis of uncultured amnion. In contrast, cytogenetic analysis of cultured amnion showed trisomy in only 2 of 20 informative cases. The molecular detection of trisomy in amnion was strongly associated with poor pregnancy outcome (intrauterine growth restriction, fetal anomalies and/or intrauterine/neonatal death) even when analysis was limited to cases negative for the trisomy on amniotic fluid (N = 22, p = 0.0005).
  
  
  CONCLUSIONS
  We infer that amniotic mesenchyme (usually diploid) derives from early embryonic mesoderm of the primitive streak and not from the hypoblast as is commonly cited. Trisomy in amniotic epithelium suggests that high numbers of abnormal cells were present in the epiblast, and this correlates with poor outcome even when the subsequently derived fetus and amniotic mesenchyme appear to carry only diploid cells.
authors.affiliation: Department of Medical Genetics, University of British Columbia, Vancouver, BC, Canada. wendyr@interchange.ubc.ca
authors.forename: Wendy P
authors.initials: WP
authors.lastname: Robinson
authors.forename: Deborah E
authors.initials: DE
authors.lastname: McFadden
authors.forename: Irene J
authors.initials: IJ
authors.lastname: Barrett
authors.forename: Brian
authors.initials: B
authors.lastname: Kuchinka
authors.forename: Maria S
authors.initials: MS
authors.lastname: Peñaherrera
authors.forename: Hélène
authors.initials: H
authors.lastname: Bruyère
authors.forename: Robert G
authors.initials: RG
authors.lastname: Best
authors.forename: Denise A L
authors.initials: DA
authors.lastname: Pedreira
authors.forename: Sylvie
authors.initials: S
authors.lastname: Langlois
authors.forename: Dagmar K
authors.initials: DK
authors.lastname: Kalousek
mesh_terms: D000015:Abnormalities, Multiple / Q000235:genetics; D000328:Adult; D000649:Amniocentesis; D000650:Amnion / Q000737:chemistry; D015193:Chorionic Villi Sampling; D004247:DNA / Q000032:analysis; D005260:Female; D005313:Fetal Death / Q000235:genetics; D005317:Fetal Growth Retardation / Q000235:genetics; D005333:Fetus / Q000502:physiology*; D005838:Genotype; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007231:Infant, Newborn; D018895:Microsatellite Repeats; D009030:Mosaicism / Q000235:genetics*; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D011256:Pregnancy Outcome; D014314:Trisomy / Q000235:genetics*; D024182:Uniparental Disomy / Q000235:genetics
chemical_list: D004247:DNA