title: Incidence of placental mosaicism leading to discrepant results between QF-PCR and karyotyping in 22,825 chorionic villus samples.
abstract: OBJECTIVE
  To review the frequency and analyse the origin of completely discrepant results observed between QF-PCR and karyotyping in chorionic villus samples (CVS) as a result of placental mosaicism. Also, to assess QF-PCR results for biallelic or triallelic patterns and determine their significance.
  
  
  METHODS
  Between May 2002 and December 2009, 22 825 CVS were received at TDL Genetics for processing by QF-PCR and karyotype. The QF-PCR and karyotype data were compared to determine the incidence of discrepant results.
  
  
  RESULTS
  Of the 22 825 samples received, 22 779 (99.8%) gave concordant results between the PCR and karyotype, and 46 samples (0.2%) gave discordant results. Of these discrepant cases, 5 displayed triallelic peaks and 41 displayed biallelic peaks. All discordant results are due to the presence of placental mosaicism, a known limitation of using this sample type for prenatal diagnosis.
  
  
  CONCLUSIONS
  This retrospective study of placental mosaicism in CVS is the largest single centre study to date and provides a figure for the occurrence of completely discrepant results between QF-PCR and karyotype due to placental mosaicism. This study also demonstrates that the presence of triallelic peaks at QF-PCR is not sufficient to exclude the presence of placental mosaicism.
authors.affiliation: Molecular Genetics, TDL Genetics, London, UK. elaine.holgado@tdlpathology.com
authors.forename: Elaine
authors.initials: E
authors.lastname: Holgado
authors.forename: Stuart
authors.initials: S
authors.lastname: Liddle
authors.forename: Terry
authors.initials: T
authors.lastname: Ballard
authors.forename: Lisa
authors.initials: L
authors.lastname: Levett
mesh_terms: D000328:Adult; D015193:Chorionic Villi Sampling / Q000379:methods*; D002869:Chromosome Aberrations; D004247:DNA / Q000032:analysis; D003951:Diagnostic Errors / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D007621:Karyotyping / Q000379:methods*; D009030:Mosaicism / Q000196:embryology*; D010922:Placenta Diseases / Q000175:diagnosis* / Q000235:genetics; D016133:Polymerase Chain Reaction / Q000379:methods*; D011247:Pregnancy; D015203:Reproducibility of Results
chemical_list: D004247:DNA