This document discusses methods for testing chromosomes in embryos, including preimplantation genetic screening (PGS). It notes that chromosome abnormalities are common in oocytes and increase with maternal age. Older techniques for PGS had limitations but new methods like microarray-based comparative genomic hybridization (CGH) allow analysis of all chromosomes and overcome many of the issues of prior techniques. Studies using CGH show reductions in aneuploidy and miscarriage rates as well as increased implantation and pregnancy rates. Gene expression analysis may also provide information about embryo viability beyond just detecting chromosome abnormalities.
3. AneuploidyAneuploidy
The incidence of aneuploidyThe incidence of aneuploidy
Chromosome abnormality is extremely common in oocytesChromosome abnormality is extremely common in oocytes
Problem increases with advancing maternal ageProblem increases with advancing maternal age
40%40%
10%10%
20%20%
30%30%
2020--3434 3535--3939 4040--4545 Maternal ageMaternal age
50%50%
Also reflected in the increase in Down syndrome with ageAlso reflected in the increase in Down syndrome with age
4. AneuploidyAneuploidy
Aneuploidy and IVF failureAneuploidy and IVF failure
As aneuploidy increases age, so implantation rate decreasesAs aneuploidy increases age, so implantation rate decreases
40%40%
10%10%
20%20%
30%30%
2020--3434 3535--3939 4040--4545 Maternal ageMaternal age
50%50%
ImplantationImplantation
6565--75% of first trimester miscarriages are aneuploid75% of first trimester miscarriages are aneuploid
5. regularregular after chromosomeafter chromosome
screeningscreening
Standard embryo evaluations do not reveal embryos withStandard embryo evaluations do not reveal embryos with
the wrong number of chromosomesthe wrong number of chromosomes
Preimplantation genetic screeningPreimplantation genetic screening
oror
6. Chromosomal indicationsChromosomal indications
Preimplantation genetic screeningPreimplantation genetic screening
22--3 rounds of FISH3 rounds of FISHBiopsyBiopsy
Reduce aneuploid syndromesReduce aneuploid syndromes
Reduce miscarriageReduce miscarriage
Increase embryo implantation/pregnancy rateIncrease embryo implantation/pregnancy rate
Reduce incidence of highReduce incidence of high--order multiplesorder multiples rate ?rate ?
Anticipated benefits for IVF patientsAnticipated benefits for IVF patients
7. Reduction in aneuploidies 13, 18, 21, XY achieved using PGSReduction in aneuploidies 13, 18, 21, XY achieved using PGS
From 2,300 cases with followFrom 2,300 cases with follow--up data available, mean age 37up data available, mean age 37
PGSPGS –– reduction in aneuploid pregnancyreduction in aneuploid pregnancy
Munne et al 2006 and Reprogenetics data to 10/2007Munne et al 2006 and Reprogenetics data to 10/2007
2.60%
0.50%
0.00%
0.50%
1.00%
1.50%
2.00%
2.50%
3.00%
trisomic conceptions
expected
observed
P<0.001P<0.001
8. PGSPGS –– reduction in aneuploid pregnancyreduction in aneuploid pregnancy
Are patients interested in PGS for this purpose?Are patients interested in PGS for this purpose?
If PGS was assumed to have no effect on pregnancy rateIf PGS was assumed to have no effect on pregnancy rate
Recent study of subfertile women (Twisk et al., 2007)Recent study of subfertile women (Twisk et al., 2007)
83% of patients would request PGS83% of patients would request PGS
If PGS was assumed to reduce pregnancy rate from 20% to 14%If PGS was assumed to reduce pregnancy rate from 20% to 14%
36% of patients would still request PGS36% of patients would still request PGS
(75% if 80% detection)(75% if 80% detection)
(31% if 80% detection)(31% if 80% detection)
9. •• Screening clearly reduces incidence of Down syndromeScreening clearly reduces incidence of Down syndrome
•• Miscarriage rate is probably reducedMiscarriage rate is probably reduced
•• Increase in pregnancy/birth rate remains controversialIncrease in pregnancy/birth rate remains controversial
•• New methods may have finally solved controversyNew methods may have finally solved controversy
Increase in implantation/pregnancyIncrease in implantation/pregnancy-- controversycontroversy
10. Problems with older technologiesProblems with older technologies
Former technologies only permitted analysis of a restrictedFormer technologies only permitted analysis of a restricted
set of chromosomesset of chromosomes
Cells are in interphaseCells are in interphase
Limited range of fluorochromesLimited range of fluorochromes
Errors caused by spreadingErrors caused by spreading
-- use FISHuse FISH
11. Problems with older technologiesProblems with older technologies
Less than half the chromosomes are currently testedLess than half the chromosomes are currently tested
Former technologies only permitted analysis of a restrictedFormer technologies only permitted analysis of a restricted
set of chromosomesset of chromosomes
Cells are in interphaseCells are in interphase
Errors caused by spreadingErrors caused by spreading
MosaicismMosaicism
Limited range of fluorochromesLimited range of fluorochromes
Poses a significant problemPoses a significant problem
for diagnosis. However,for diagnosis. However,
51% of embryos are51% of embryos are
aneuploid in every cell.aneuploid in every cell.
12. •• RapidRapid –– results in 24 hoursresults in 24 hours
•• Allows the copy number of every chromosome to be determinedAllows the copy number of every chromosome to be determined
NormalNormalTrisomyTrisomy MonosomyMonosomy
Normal DNANormal DNAEmbryo DNAEmbryo DNA
Microarray comparative genomic hybridizationMicroarray comparative genomic hybridization
14. Clinical application of CGHClinical application of CGH
•• 100% of chromosome losses/gains detected100% of chromosome losses/gains detected
BenefitsBenefits
•• DNADNA--basedbased
•• No spreadingNo spreading
15. Diagnosis more robust and accurateDiagnosis more robust and accurate
•• Biopsy of several cells is possibleBiopsy of several cells is possible
Less risk of misdiagnosis due to mosaicismLess risk of misdiagnosis due to mosaicism
Analysis of blastocyst stageAnalysis of blastocyst stage
•• Can overcoming the principal challenges to accurate screeningCan overcoming the principal challenges to accurate screening
allow PGS to fulfill the potential predicted by theory?allow PGS to fulfill the potential predicted by theory?
Little or no impact of embryo biopsyLittle or no impact of embryo biopsy
•• Blastocyst cryopreservation (vitrification) necessaryBlastocyst cryopreservation (vitrification) necessary
Clinical application of CGHClinical application of CGH
16. •• Near 98% survival after biopsy, freeze and thawNear 98% survival after biopsy, freeze and thaw
•• 170 patients, mean age 38 years, 1170 patients, mean age 38 years, 1--6 previous failed IVF cycles6 previous failed IVF cycles
(mean 2 failed attempts)(mean 2 failed attempts)
•• Birth rate per cycle with transferBirth rate per cycle with transfer 79%79%
•• Implantation rate per embryoImplantation rate per embryo 67%67%
Blastocyst CGHBlastocyst CGH-- clinical resultsclinical results
60%60%
28%28% **
Control group matched for: maternal age, dayControl group matched for: maternal age, day--3 FSH, day of transfer, # oocytes3 FSH, day of transfer, # oocytes
retrieved, # of failed cyclesretrieved, # of failed cycles
*p<0.0003*p<0.0003 -- Extremely promising for single embryo transferExtremely promising for single embryo transfer
17. •• Embryo loss rates are lowEmbryo loss rates are low
•• 91% of embryos that produced a fetal sac resulted in an91% of embryos that produced a fetal sac resulted in an
ongoing third trimester pregnancy or live birthongoing third trimester pregnancy or live birth
•• 97% of embryos that produced a fetal heart beat resulted in an97% of embryos that produced a fetal heart beat resulted in an
ongoing third trimester pregnancy or live birthongoing third trimester pregnancy or live birth
•• Expected pregnancy loss rate for IVF patients in this ageExpected pregnancy loss rate for IVF patients in this age
range is ~25%range is ~25%
Blastocyst CGHBlastocyst CGH-- rates of pregnancy lossrates of pregnancy loss
18. Blastocyst CGHBlastocyst CGH-- clinical resultsclinical results
Implantation rate
Aneuploidy rate
Cycles with all embryos
aneuploid
Patients aged 30Patients aged 30--40 who are eligible for blastocyst transfer40 who are eligible for blastocyst transfer
(according to day(according to day--3 criteria) have a >95% chance of having3 criteria) have a >95% chance of having
normal embryos available for transfernormal embryos available for transfer
19. R. Scott et al (reported at ASRM 2008):R. Scott et al (reported at ASRM 2008):
•• Blinded prospective studyBlinded prospective study
•• Embryos biopsied at cleavage stageEmbryos biopsied at cleavage stage
•• Copy number of all chromosomes tested using a microarrayCopy number of all chromosomes tested using a microarray
•• Embryos transferred after biopsy, but before aneuploidyEmbryos transferred after biopsy, but before aneuploidy
resultresult
Other new data using comprehensive aneuploidyOther new data using comprehensive aneuploidy
screening methodsscreening methods
Retrospective analysis of IVF outcome revealed the following:Retrospective analysis of IVF outcome revealed the following:
•• 0/31 aneuploid embryos produced a child0/31 aneuploid embryos produced a child
•• 26 implantation failure, 5 miscarriages26 implantation failure, 5 miscarriages
•• 100% negative predictive value100% negative predictive value
20. •• After CGH pregnancy rates were above those typicallyAfter CGH pregnancy rates were above those typically
achieved for all age groups.achieved for all age groups.
•• However, pregnancy rates were lower for older patients due toHowever, pregnancy rates were lower for older patients due to
the increased frequency of cycles with no euploid embryos.the increased frequency of cycles with no euploid embryos.
•• Spontaneous abortion rates were reduced for all patients,Spontaneous abortion rates were reduced for all patients,
including those with a history of multiple miscarriageincluding those with a history of multiple miscarriage
•• Chromosomally normal embryos from older patients have aChromosomally normal embryos from older patients have a
similar chance of producing a child as those derived fromsimilar chance of producing a child as those derived from
young patients.young patients.
•• Aneuploidy is likely to be the principal factor causing reducedAneuploidy is likely to be the principal factor causing reduced
IVF success with advancing maternal ageIVF success with advancing maternal age
ConclusionsConclusions
21. •• Can the results obtained in the current study be replicated inCan the results obtained in the current study be replicated in
a randomized controlled trial?a randomized controlled trial?
•• What patient groups will benefit the most from this type ofWhat patient groups will benefit the most from this type of
screening?screening?
QuestionsQuestions
•• How much of the observed benefit for blastocyst screening isHow much of the observed benefit for blastocyst screening is
due to transfer in a subsequent cycle?due to transfer in a subsequent cycle?
•• Aneuploidy explains most of the decline in IVF success withAneuploidy explains most of the decline in IVF success with
advancing maternal age. What explains the remainder?advancing maternal age. What explains the remainder?
23. Identifying new viability markersIdentifying new viability markers ––
gene expressiongene expression
Analysis of gene expression:Analysis of gene expression:
may provide detailed information concerning viabilitymay provide detailed information concerning viability
may reveal the basis of underlying biological problemsmay reveal the basis of underlying biological problems
indicates the processes occurring within a cellindicates the processes occurring within a cell
disturbances of expression associated with morphologicaldisturbances of expression associated with morphological
abnormalitiesabnormalities
Not even transfer of morphologically normal euploidNot even transfer of morphologically normal euploid
embryos can guarantee a pregnancyembryos can guarantee a pregnancy
25. 4-10 cell embryo with
multinucleation
Wells et al., Hum. Reprod. & Fertil. Steril. (2005)
Gene expression, stage & morphology
Pre-genome activation
2-cells, 3-cells, early 4-cells
Oocytes
Morulae
Blastocysts
(hatching)
2-10 cell embryos
BRCA1-
Roles in repair of
DNA damage
(chromosome
breakage) and
chromosome
segregation
26. Genes with lowGenes with low
levels oflevels of
expressionexpression
Genes with highGenes with high
levels oflevels of
expressionexpression
Genes showingGenes showing
differentialdifferential
expressionexpression
Gene expression microarraysGene expression microarrays
Gene expression microarrayGene expression microarray-- simultaneous analysis of 1000s ofsimultaneous analysis of 1000s of
genesgenes
Supported by educational grant from EMD SeronoSupported by educational grant from EMD Serono
27. •• Identify malfunctioning cellular mechanisms resultingIdentify malfunctioning cellular mechanisms resulting
in aneuploidyin aneuploidy
•• Identify new nonIdentify new non--invasive markers of oocyte aneuploidyinvasive markers of oocyte aneuploidy
Aneuploidy and oocyte/cumulus cell gene expressionAneuploidy and oocyte/cumulus cell gene expression
•• The origin of aneuploidy is poorly understoodThe origin of aneuploidy is poorly understood
28. Polar
body
Reverse transcription
mRNA converted to cDNA
RNA purification
Second strand cDNA synthesis
Double stranded cDNA produced
In vitro transcription
ds-cDNA used as a template
for RNA synthesis
Cell lysis
Whole genome amplification
Cytogenetic analysis
CGH
Reverse transcription
RNA converted to cDNA
Second strand cDNA
synthesis
ds-cDNA produced
1st round of amplification
In vitro transcription and
cRNA labelling
ds-cDNA used as a template
for RNA synthesis
Microarray analysis
2nd
round of amplification
Cumulus
cells
Oocyte
Real-time PCR
29. ResultsResults
261 genes with statistically significant differences261 genes with statistically significant differences
(213 genes p<0.05; 48 genes p<0.01)(213 genes p<0.05; 48 genes p<0.01)
Altered genes include several involved with spindle dynamics,Altered genes include several involved with spindle dynamics,
chromatin structure and cell cycle regulationchromatin structure and cell cycle regulation
Several genes producingSeveral genes producing cell surfacecell surface oror secretedsecreted proteins areproteins are
differentially expresseddifferentially expressed
Aneuploidy and the oocyte transcriptomeAneuploidy and the oocyte transcriptome
30. Oocyte aneuploidy and the cumulus cell transcriptomeOocyte aneuploidy and the cumulus cell transcriptome
•• Comparison of cumulus cells associated with aneuploid orComparison of cumulus cells associated with aneuploid or
normal oocytes:normal oocytes:
Differential gene expression for 752 genesDifferential gene expression for 752 genes
(125 p<0.01, 627 p<0.05)(125 p<0.01, 627 p<0.05)
•• Principal processes alteredPrincipal processes altered……....
ResultsResults
31. Cellular pathways altered in cumulus cellsCellular pathways altered in cumulus cells
associated with aneuploid oocytesassociated with aneuploid oocytes
HormonesHormones
Stress pathwaysStress pathways
HypoxiaHypoxia
Nutritional deprivationNutritional deprivation
Cumulus cellCumulus cell
proliferationproliferation
Cumulus cellCumulus cell
apoptosisapoptosis
DifferentiationDifferentiation
*Known association with oocyte quality*Known association with oocyte quality
AgeAge AneuploidyAneuploidy
32. ConclusionsConclusions
Aneuploidy and cumulus cell gene expressionAneuploidy and cumulus cell gene expression
•• Support of specific pathways (in vivo/in vitro) may reduceSupport of specific pathways (in vivo/in vitro) may reduce
aneuploidy. Reduce maternal age affectaneuploidy. Reduce maternal age affect
•• Follicular environment influences oocyte aneuploidy ratesFollicular environment influences oocyte aneuploidy rates
•• Targets for indirect detection of chromosome anomaliesTargets for indirect detection of chromosome anomalies
14 genes have differential expression (P<0.01)14 genes have differential expression (P<0.01)
and fold change >4and fold change >4
•• Altered genes link aneuploidy and ageAltered genes link aneuploidy and age--related hormonalrelated hormonal
changeschanges
