Rapid prenatal diagnosis of common trisomies: discordant results between QF-PCR analysis and karyotype analysis on long-term culture for a case of trisomy 18 detected in CVS.
OBJECTIVE
QF-PCR analysis can be used as a rapid test to diagnose primary trisomy in prenatal samples. Mosaicism in CVS detected by QF-PCR has previously been reported; however, no case has so far been reported in which the QF-PCR result was completely discrepant to that of the karyotype analysis from a long-term culture.


METHODS
A CVS, referred because of a high serum screening risk of 1:10 for Down Syndrome and 1:110 for Edwards Syndrome, was tested by QF-PCR analysis and chromosome analysis of cultured cells. Subsequent analyses were carried out on a follow-up amniotic fluid sample and foetal tissue samples.


RESULTS
Conflicting results were obtained between QF-PCR analysis on two independent fronds from the chorionic villi and chromosome analysis on cultured CVS. Cytogenetic and molecular analysis on a subsequent amniotic fluid sample indicated trisomy 18 with no evidence of mosaicism. Analysis of follow-up tissue confirmed trisomy in a foetal skin sample and mosaicism for trisomy 18 in four placental sites tested.


CONCLUSIONS
We report here an apparently normal CVS QF-PCR result that was completely discrepant with the trisomy 18 positive karyotype result on long-term culture. This has important implications regarding our current testing protocol.
Allen
S K
SK
West Midlands Regional Genetics Laboratory, Birmingham Women's Hospital, Edgbaston, Birmingham B15 2TG. stephanie.allen@bwhct.nhs.uk
Luharia
A
A
Gould
C P
CP
MacDonald
F
F
Larkins
S
S
Davison
E V
EV
D000328:Adult; D018929:Cell Culture Techniques; D015193:Chorionic Villi Sampling / Q000379:methods*; D025063:Chromosome Disorders / Q000175:diagnosis*; D002887:Chromosomes, Human, Pair 18; D005260:Female; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007621:Karyotyping / Q000379:methods*; D016133:Polymerase Chain Reaction / Q000379:methods*; D011247:Pregnancy; D012867:Skin / Q000473:pathology; D014314:Trisomy