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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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Data from 3 London labsData from 3 London labs

01/05/2007 – 30/11/2007

Consortium samples only

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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

normal/trisomy97%

abnormality not detected by QF-

PCR3%

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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