Evidence-Based Strategies Evidence-Based Strategies for Prenatal Maternal for Prenatal Maternal

ScreeningScreening

GeneticScreeningWRAPGeneticScreeningWRAP

Wayne W. Grody, MD, PhDWayne W. Grody, MD, PhDProfessor and DirectorProfessor and Director

Diagnostic Molecular Pathology LaboratoryDiagnostic Molecular Pathology LaboratoryDepartment of Pediatrics and Human GeneticsDepartment of Pediatrics and Human Genetics

David Geffen School of Medicine at UCLADavid Geffen School of Medicine at UCLALos Angeles, CaliforniaLos Angeles, California

Indications for Prenatal DiagnosisIndications for Prenatal Diagnosis

► Maternal ageMaternal age

► Positive family history for a genetic Positive family history for a genetic disorderdisorder

► Presence of a chromosome Presence of a chromosome abnormality in a abnormality in a parent parent

► Population screening; parent(s) found Population screening; parent(s) found to be carrier of mutationto be carrier of mutation

Grody, Grody, Annu. Rev. MedAnnu. Rev. Med. 2003. 2003

Disease Criteria for Population Disease Criteria for Population Genetic Risk ScreeningGenetic Risk Screening

1.1. Relatively commonRelatively common

2.2. Relatively seriousRelatively serious

3.3. Manageable number of predominant mutationsManageable number of predominant mutations

4.4. High penetranceHigh penetrance

5.5. Defined and consistent natural historyDefined and consistent natural history

6.6. Effective preventive or surveillance interventionsEffective preventive or surveillance interventions

7.7. Mutation detection relatively inexpensiveMutation detection relatively inexpensive

8.8. Screening test acceptable to populationScreening test acceptable to population

9.9. Infrastructure in place for pre- and post-test educationInfrastructure in place for pre- and post-test education

1.1. Target ascertainment (age, ethnicity, etc.)Target ascertainment (age, ethnicity, etc.)

2.2. Test offeringTest offering

3.3. Pre-test educationPre-test education

4.4. Informed consent (if applicable)Informed consent (if applicable)

5.5. Analytic phase (DNA test)Analytic phase (DNA test)

6.6. Results interpretation and reportingResults interpretation and reporting

7.7. Post-test counselingPost-test counseling

Key Components of the Genetic Risk Key Components of the Genetic Risk Screening ProcessScreening Process

Grody, Grody, Annu. Rev. MedAnnu. Rev. Med. 2003. 2003

Grody, Grody, Annu. Rev. MedAnnu. Rev. Med. 2003. 2003

Candidate Diseases for Inclusion in Candidate Diseases for Inclusion in an Ashkenazi-Jewish Screening Panelan Ashkenazi-Jewish Screening Panel

DiseaseDisease Carrier frequency Carrier frequency in target populationin target population

Tay-Sachs diseaseTay-Sachs disease 1/271/27Cystic fibrosisCystic fibrosis 1/291/29Gaucher diseaseGaucher disease 1/151/15Canavan diseaseCanavan disease 1/361/36Familial dysautonomiaFamilial dysautonomia 1/301/30Connexin-26 deafnessConnexin-26 deafness 1/261/26Familial Mediterranean feverFamilial Mediterranean fever 1/71/7Niemann-Pick disease, type ANiemann-Pick disease, type A 1/851/85Fanconi anemia, group CFanconi anemia, group C 1/851/85Bloom syndromeBloom syndrome 1/1001/100

Summary of ACMG Recommendations forSummary of ACMG Recommendations forPopulation-based Cystic Fibrosis Carrier ScreeningPopulation-based Cystic Fibrosis Carrier Screening

1.1. Testing should be offered to Caucasians and Testing should be offered to Caucasians and Ashkenazi Jews, and made available to all other Ashkenazi Jews, and made available to all other ethnic groups.ethnic groups.

2.2. Either simultaneous or sequential couple screening Either simultaneous or sequential couple screening may be used, as long as results are given to both may be used, as long as results are given to both partners.partners.

3.3. A universal, pan-ethnic core mutation panel should A universal, pan-ethnic core mutation panel should

be used, consisting of:be used, consisting of:► 25 mutations25 mutations► 3 exonic polymorphisms as reflex tests3 exonic polymorphisms as reflex tests► 5/7/9T intronic polymorphism as reflex test 5/7/9T intronic polymorphism as reflex test

only if only if

R117H is positive R117H is positiveGrody et al., Genet. Med. 2001

Summary of ACMG Recommendations forSummary of ACMG Recommendations forPopulation-based Cystic Fibrosis Carrier ScreeningPopulation-based Cystic Fibrosis Carrier Screening

4.4. Extended mutation panels for positive-negative couples Extended mutation panels for positive-negative couples should not be offered or encouraged.should not be offered or encouraged.

5.5. Reporting of results and residual risks should be based on Reporting of results and residual risks should be based on the detection rates and model report forms developed by the detection rates and model report forms developed by the committee.the committee.

6.6. Primary care providers not comfortable with the Primary care providers not comfortable with the complexities of these reports should refer the couple to a complexities of these reports should refer the couple to a genetics professional. genetics professional.

7.7. Quality assurance standards should adhere to the Quality assurance standards should adhere to the guidelines of ACMG, CAP, and the NIH-DOE Task Force guidelines of ACMG, CAP, and the NIH-DOE Task Force on Genetic Testing.on Genetic Testing.

Grody et al., Genet. Med. 2001

F508F508 I507I507 G542X G551D G542X G551D W1282X N1303K W1282X N1303KR553XR553X 621+1G>T 621+1G>T R117H 1717-1G>A A455E R560T R117H 1717-1G>A A455E R560TR1162X G85ER1162X G85E R334W R347P 711+1G>T 1898+1G>A R334W R347P 711+1G>T 1898+1G>A2184delA 1078delT*2184delA 1078delT* 3849+10kbC>T 2789+5G>A 3659delC I148T* 3849+10kbC>T 2789+5G>A 3659delC I148T*3120+1G>A3120+1G>A

†Grody et al., Genet. Med. 2001

*Removed from panel in 2004 (Watson et al., Genet. Med. 2004)

Recommended Core Mutation Panel forRecommended Core Mutation Panel forGeneral Population CF Carrier ScreeningGeneral Population CF Carrier Screening††

Nationwide CF Carrier Screening:Nationwide CF Carrier Screening:Revelations from “Post-market Surveillance”Revelations from “Post-market Surveillance”

1.1. Low OB penetrationLow OB penetration

2.2. Panel mutation that is less frequent Panel mutation that is less frequent than expected: 1078delTthan expected: 1078delT

3.3. Panel mutation that is not a mutation: Panel mutation that is not a mutation: I148TI148T

4.4. Additional non-panel mutations that Additional non-panel mutations that could qualify for inclusion: E60X, could qualify for inclusion: E60X, Q493X, S549N, 2183delAA>G, Q493X, S549N, 2183delAA>G, Y1092X, etc.Y1092X, etc.

5.5. Mutation screening panel “inflation”Mutation screening panel “inflation”

Concerns About Expanded Mutation PanelsConcerns About Expanded Mutation Panels

► Departs from endorsed standard of care Departs from endorsed standard of care (ACMG/ACOG)(ACMG/ACOG)

► Added costAdded cost► False sense of securityFalse sense of security► Arbitrary selection of low-frequency variantsArbitrary selection of low-frequency variants► Uncertain allele frequency data for rare variantsUncertain allele frequency data for rare variants► Why not just go directly to full sequencing?Why not just go directly to full sequencing?► Paucity of genotype-phenotype correlation dataPaucity of genotype-phenotype correlation data► Unseemly competition: “mutation arms race”Unseemly competition: “mutation arms race”► Potential for limited access or monopolizationPotential for limited access or monopolization► Law of diminishing returns: sensitivity claims belied Law of diminishing returns: sensitivity claims belied

by field experience thus farby field experience thus far► The paradox of dwindling predictive valueThe paradox of dwindling predictive value► Social/religious/genetic considerations in ethnic Social/religious/genetic considerations in ethnic

targetingtargeting

► Suboptimal test sensitivitySuboptimal test sensitivity► Ethnic differencesEthnic differences► Education and counselingEducation and counseling► Anxiety and stigmatizationAnxiety and stigmatization► Informed consentInformed consent► ConfidentialityConfidentiality► InsurabilityInsurability► Genetic and clinical burdenGenetic and clinical burden► AbortionAbortion

Ethical Issues in Cystic Fibrosis Ethical Issues in Cystic Fibrosis Mutation ScreeningMutation Screening

Chromosome Disorders Are A Major Chromosome Disorders Are A Major Category of Genetic DiseaseCategory of Genetic Disease

► Nearly 1% of live birthsNearly 1% of live births

► Approx 2% of prenatal diagnoses in Approx 2% of prenatal diagnoses in women >35 yrs oldwomen >35 yrs old

► 50% of all first trimester 50% of all first trimester spontaneous abortionsspontaneous abortions

What are the Indications for Ordering What are the Indications for Ordering a Chromosome Analysis?a Chromosome Analysis?

► Growth and Growth and developmental developmental abnormalitiesabnormalities

► Family history of Family history of chromosome chromosome abnormalitiesabnormalities

► Pregnancy with Pregnancy with “advanced maternal “advanced maternal age” (AMA)age” (AMA)

► Stillbirth/neonatal Stillbirth/neonatal deathdeath

► Infertility/history of Infertility/history of pregnancy losspregnancy loss

► NeoplasiaNeoplasia

Maternal Serum Alpha-FetoproteinMaternal Serum Alpha-Fetoprotein

► MSAFPMSAFP► Increased with open neural tube Increased with open neural tube

defectdefect► Test at 16 weeksTest at 16 weeks► ““MoM” = Multiple of the medianMoM” = Multiple of the median

Triple Marker ScreenTriple Marker Screen

► AFP, uE3, hCGAFP, uE3, hCG

► Screens for NTD, Down syndrome, Screens for NTD, Down syndrome, trisomy 18trisomy 18

► Tested at 15-20 weeksTested at 15-20 weeks

► Based on MoMBased on MoM

► AFP and uE3 decreased in trisomiesAFP and uE3 decreased in trisomies

► hCG increased in trisomy 21, decreased hCG increased in trisomy 21, decreased in trisomy 18in trisomy 18

Triple Marker Screen ResultsTriple Marker Screen Results

Risk of Down Syndrome Risk of Down Syndrome by Maternal Ageby Maternal Age

Maternal Age Risk

20 1/1,667

29 1/1,000

34 1/500

40 1/106

45 1/30

49 1/11

Fragile X Clinical FeaturesFragile X Clinical Features

► >90% have mental retardation; IQ 0->90% have mental retardation; IQ 0-60, mean 30-4560, mean 30-45

► In children, may present with: In children, may present with: hyperactivity, ADD, autistic features, hyperactivity, ADD, autistic features, hyperextensible joints, mitral prolapsehyperextensible joints, mitral prolapse

► After puberty: macroorchidism, long After puberty: macroorchidism, long face with large ears and prominent jawface with large ears and prominent jaw

CGG Repeat in Fragile X SyndromeCGG Repeat in Fragile X Syndrome

• Normal range: 6-54 repeats

• Premutation range: 52-200 repeats

• Full mutation range: 200- >1000 repeats

• Alleles with >200 repeats are hypermethylated, transcriptionally repressed

Length of Maternal PremutationLength of Maternal PremutationIncidence of Full Mutation in OffspringIncidence of Full Mutation in Offspring

56-59 13%

60-69 20%

70-79 58%

80-89 73%

90-99 94%

100-109 100%

120-129 100%

Nolin et al., Am. J. Hum. Genet. 1996

Is the Fragile X Premutation Is the Fragile X Premutation Really Asymptomatic?Really Asymptomatic?

► Recent reports of premature ovarian Recent reports of premature ovarian failure in female premutation carriersfailure in female premutation carriers

► Late-onset tremor-ataxia-dementia Late-onset tremor-ataxia-dementia syndrome in male premutation carrierssyndrome in male premutation carriers

► May be due to mRNA interference with May be due to mRNA interference with expression of the normal expression of the normal FMR1FMR1allele or allele or of other genesof other genes

Fetal Cells in Maternal BloodFetal Cells in Maternal Blood

► Present in very small numbersPresent in very small numbers

► Requires highly sensitive PCR and/or cell Requires highly sensitive PCR and/or cell sortingsorting

► Beware of long-lived fetal lymphocytesBeware of long-lived fetal lymphocytes

GeneticScreeningWRAPGeneticScreeningWRAP