Origin of amnion and implications for evaluation of the fetal genotype in cases of mosaicism.
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.
Robinson
Wendy P
WP
Department of Medical Genetics, University of British Columbia, Vancouver, BC, Canada. wendyr@interchange.ubc.ca
McFadden
Deborah E
DE
Barrett
Irene J
IJ
Kuchinka
Brian
B
Peñaherrera
Maria S
MS
Bruyère
Hélène
H
Best
Robert G
RG
Pedreira
Denise A L
DA
Langlois
Sylvie
S
Kalousek
Dagmar K
DK
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
D004247:DNA