Post on 15-Dec-2015
transcript
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QF-PCR stand-alone prenatal diagnosis: QF-PCR stand-alone prenatal diagnosis: the initial London experience.the initial London experience.
Caroline Mackie Ogilvie
Cytogenetics Department
Guy’s Hospital
London
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Guy’s QF-PCR dataGuy’s QF-PCR data
2000 - 2007
Total samples tested: 23,311
CVS 6729 (28.9%)
AF 16582 (71.1%)
97% of samples receive a result within one working day
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Should we karyotype pregnancies at Should we karyotype pregnancies at risk of Down syndrome?risk of Down syndrome?
• 32,674 pregnant women having invasive PND in London/South East
• 24,891 (76.2%) were referred for exclusion of Down syndrome
• others at risk of single gene disorders or complex chromosome abnormalities
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• 24,891 pregnancies referred for exclusion of T21
• 118 sex chromosome abnormalities
• 153 other abnormalities
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Good prognosisGood prognosis::
– balanced rearrangementsbalanced rearrangements– variant regionsvariant regions
Uncertain prognosisUncertain prognosis::
– small marker chromosomessmall marker chromosomes– mosaic anomaliesmosaic anomalies
Poor prognosisPoor prognosis
– non-mosaic genomic imbalancenon-mosaic genomic imbalance
Abnormal karyotypes:Abnormal karyotypes:
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Trisomy risk referralsTrisomy risk referrals
00
2020
4040
6060
8080
100100
120120
140140
SexSex GPGP UPUP PPPP
n
n=24,891
0.47%0.47% 0.39%0.39% 0.15%0.15% 0.07%0.07%
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Poor Prognosis n = 18Poor Prognosis n = 18
1 liveborn (10q del) minor facial dysmorphism but normal development at 20 months
2 miscarried
4 outcome unknown, of which 1 = T16, 2 = 46,XX,del(18), 1=46,XX,add(9)
11 TOP (61%)
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Advantages of QF-PCR stand-alone Advantages of QF-PCR stand-alone testingtesting
• uncertain or harmless karyotypes not detected, reducing anxiety and follow-up studies
• no residual anxiety while waiting for karyotype results
• better use of resources
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New service May 2007New service May 2007
All abnormal QF-PCR results followed up by karyotype analysis
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Criteria for karyotypingCriteria for karyotyping
Clinical indication, viz:
• structural abnormality on U/S
• 2 or more soft markers for trisomy 21
• nuchal measurement >3mm at below 14 weeks gestation
• nuchals measurement >6mm for gestations >= 14 weeks
• family history of chromosome rearrangement
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QF-PCR + karyotype
21%
QF-PCR79%
AF samples AF samples n=1502n=1502
Karyotype only1%
QF-PCR only54%
QF-PCR + karyotype
45%
CVS samples CVS samples n=628n=628
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Abnormals not
detected by QF-PCR
11%
QF-PCR abnormals
89%
Abnormals not
detected by QF-PCR
15%
QF-PCR abnormals
85%
AF abnormals AF abnormals n=122n=122
CVS abnormals CVS abnormals n=n=135135
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Abnormalities not detected by Abnormalities not detected by QF-PCRQF-PCR
Detection rate in karyotyped AF 3%
Detection rate in karyotyped CVS 7%
No abnormal babies reported to date.
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One pregnancy:• QF-PCR only at CVS• ultrasound showed severe IUGR and abnormal placenta
at 26 weeks • follow-up amnio: mos tetraploidy • pregnancy terminated • fetal blood showed normal karyotype
Tetraploid cell line probably confined to placenta leading to placental insufficiency
Abnormalities not detected by Abnormalities not detected by QF-PCRQF-PCR
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NT >3mm<4mmNT >3mm<4mm
“An alternative strategy whereby qf-PCR is the main method of analysis and full karyotyping is reserved for those cases with a minimum fetal NT thickness of 4 mm would require full karyotyping in 10.1% of the cases, would identify 99.0% of the significant abnormalities, and would cost 60% less than full karyotyping for all.”
Chitty et al. (2006) BMJ 25;332(7539):452-5.
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NT >3mm<4mmNT >3mm<4mm
2 abnormal karyotypes in this group• 47,XY,+22• 47,XX,+mar[19]/46,XX[28]
– v small non-satellited marker, apparently all heterochromatin
– ?CPM– follow-up amnio and parental bloods requested, but
not forthcoming– pregnancy terminated
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CollaboratorsCollaborators
Guy’s NEL Regional Cyto Lab NWT Regional Cyto Lab (GOSH) (KGC)
Kathy MannKathy Mann Jonathan Waters Jonathan Waters Richard Ellis Richard Ellis
Zoe DochertyZoe Docherty Melissa Holloway Melissa Holloway Janine Burbridge Janine Burbridge
Sandra EdwardsSandra Edwards
Deborah MorroghDeborah Morrogh