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Nuances in Prenatal Carrier Screening

Brian L Shaffer MD

Assistant Professor

Department of Obstetrics and Gynecology

Division of Perinatal Medicine and Genetics

University of California, San Francisco

10/28/2010

Objectives – Carrier Screening

• Review available evidence:• Unique role: Women through all stages of life

• Family history: Refer for counseling

• Preconception/Prenatal

• “Ethnicity” versus Universal – benefits & limitations• Hemoglobinopathies

• Ashkenazi/Eastern European

• Cystic Fibrosis

• Fragile X

• Spinal Muscular Atrophy

• Basics of Carrier Screening

Successful Screening Program

• Disease• Considerable clinical severity

• Frequency

• Test• Reliable

• Timely

• Cost effective/ relatively inexpensive• Afford carrier screen & prenatal diagnosis

• Appropriate counseling & education• Non-directive

Successful Screening Program

• Prevention• Forgo pregnancy

• Adoption

• Donor

• IVF-PGD

• Prenatal diagnosis with option of termination

• Additional benefit• Preparation

• Education

• Delivery at an appropriate institution

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Geographic ancestry

• “Ethnicity” based

• Founder effect

• Close proximity

• Religious, geographical, political

• In general, asymptomatic

• Advantage

• Sickle cell anemia

• Does not apply to all single gene disorders

• Tay Sachs vs. Spinal Muscular Atrophy (SMA)

• Unique California population

Case• 22 year old G1P0 Thai woman presents at 22 wks for routine prenatal care

• Do you offer her Hemoglobinopathy screening?

• If so, What tests?

• What if she described her ethnicity as

• Southern Chinese, Middle Eastern, African?

• Mixed?

• Not sure?

Structure of hemoglobin

b1

b2

a1

a2

a3

a4

Beta globin genes Alpha globin genes

Chromosome 11Chromosome 16

Hemoglobin

protein

Hemoglobinopathies – ACOG

• ACOG (2007)

• African, SE Asian, Mediterranean (ACOG)

• “higher risk” for hemoglobinopathies - offer screening

• Hgb Electrophoresis/HPLC

• CBC with MCV

• Low risk

• Northern European, Japanese, Native American, Inuit, Korean

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Hemoglobinopathies – Sickle Cell

• Most common disorder Hgb

• β chain of hemoglobin

• Sub-Saharan descent

• Carrier rate: 1 in 12

• Advantage

• ~1 in 600 with SSA in US

• Diagnosis: Hgb Electrophoresis

Hemoglobinopathies – Sickle cell

• More comprehensive• African American, African, Mediterranean (Greek, Italian),

Turkish, Arabic, Southern Iranian, Asian Indian, Brazilian, Central American

• Others?

• Confirmed Hgb (α & β) abnormalities in CA by Newborn Screening

• Asian (43%)• Black (27%) • Latin (3%)• Other/Unknown (27%)

Thalassemias

• ββββ thalassemia

• Southeast Asian, Pacific Islander, Middle Eastern, Indian, Chinese, Mediterranean, African (not African American)

• Low MCV ���� Hgb Electrophoresis

• α thalassemia

• Mediterranean (Italy, Greece), East Asian (China, Thailand), Middle Eastern (Turkey, Pakistan), Central Asia (West India), African American

• Low MCV

• No evidence of iron deficiency

• Offer partner & patient molecular testing

Hemoglobinopathies – Who?

• Hemoglobin H (α – thalassemia)

• CA New born screening

• Laotian/Thai (26%) Mixed Asian (7%)

• Vietnamese (9%) Multiple race (16%)

• Cambodian (5%) Other (7%)

• Filipino (15%)

• Chinese (15%)

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Screen for Thalassemia?

• Mean corpuscular volume (MCV)

• 80fL

• Others suggest 85fL (Chan LC et al 2001)

• Those at greatest risk

• Southern Chinese, Thai/Laotian

• 80fL at UCSF

Case - continued• 22 year old G1P0 Thai woman presents at 22 wks for

routine prenatal care

• Thai – α thal, β thal

• Southern Chinese - α thal; (East Asia - β thal)

• Middle Eastern • α thal

• β thal (Turkey, Pakistan)

• SSA (Southern Iranian, Turkish, Arabic)

• African – SSA, α thal (Not African American),

• Mixed ethnicity/Not sure?• Consider Hgb electrophoresis, MCV

Case - 2• 37 year old G1P0 woman of Eastern European descent, thinks Ashkenazi presents for preconception visit

• She wants information on carrier screening

Ashkenazi/East EuropeanDisorder Incidence Carrier Freq Detection rate

Tay-Sachs 1/3,000 1/30-31 98% by enzyme

92-99% by DNA

Canavan 1/6,400-9,100 1/40-48 98%

Familial Dysautonomia 1/3,600 1/31-32 99%

Cystic Fibrosis 1/2,500-3,000 1/24/29 94-97%

Fanconi anemia-C 1/32,000 1/90 98-99%

Niemann-Pick, A 1/32,000 1/90 94-97%

Mucolipidosis, IV 1/62,500 1/127 90-95%

Bloom 1/40,000 1/107 99%

Gaucher 1/900 1/15-18 89-95%

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ACMGDisorder Incidence Carrier Freq Detection rate

Tay-Sachs 1/3,000 1/30-31 98% by enzyme

92-99% by DNA

Canavan 1/6,400-9,100 1/40-48 98%

Familial Dysautonomia 1/3,600 1/31-32 99%

Cystic Fibrosis 1/2,500-3,000 1/24/29 94-97%

Fanconi anemia-C 1/32,000 1/90 98-99%

Niemann-Pick, A 1/32,000 1/90 94-97%

Mucolipidosis, IV 1/62,500 1/127 90-95%

Bloom 1/40,000 1/107 99%

Gaucher 1/900 1/15-18 89-95%

ACOGDisorder Incidence Carrier Freq Detection rate

Tay-Sachs 1/3,000 1/30-31 98% by enzyme

92-99% by DNA

Canavan 1/6,400-9,100 1/40-48 98%

Familial Dysautonomia 1/3,600 1/31-32 99%

Cystic Fibrosis 1/2,500-3,000 1/24/29 94-97%

Fanconi anemia-C 1/32,000 1/90 98-99%

Niemann-Pick, A 1/32,000 1/90 94-97%

Mucolipidosis, IV 1/62,500 1/127 90-95%

Bloom 1/40,000 1/107 99%

Gaucher 1/900 1/15-18 89-95%

Geographic Ancestry

• Tay Sachs

• Pennsylvania Dutch

• Louisiana Cajun

• French Canadian

Case - 2• 37 year old G1P0 woman of Eastern European descent, she thinks Ashkenazi presents for preconception visit

• She wants information on carrier screening

• ACOG – standard of care

• ACMG - ? All nine

• Refer for counseling?

• Commercial company carrier screen?

• >100 diseases, ~350$

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Case- 3• 29 year old G1P0 White woman presents at 12 weeks and is concerned about cystic fibrosis (CF)

• Her husband is from Africa and neither have a personal or family history of CF.

• Your patient’s carrier screening is negative.

• ACMG 23 mutation panel reveals no mutations

• Is this enough mutations?

• What is their risk of having an affected child?

• What if mother was a carrier?

ACMG/ACOG Guidelines (2005)

CF testing should be offered to:

• Individuals with a family history of CF

• Partners of individuals with CF

• Couples in whom one or both partners are Caucasian & who are currently planning a pregnancy or seeking prenatal care

• Testing should be made available to couples who are of other ethnicities

ACMG/ACOG Guidelines (2005)

• Reality: 2/3 of all Ob/Gyn’s perform CF carrier testing on all of their patients, regardless of ethnicity

• Why?

• Increasing difficulty in assigning one ethnicity

• Does test performance differ from one ethnicity to another?

• Limitations based on geographic ancestry

• Decreased sensitivity is acceptable if patient understands

CF screening

• CFTR gene

• > 1300 mutations

• ACMG/ACOG recommendation:

• 23 most common mutations

• ‘Classic’ – severe disease

• 0.1%

• DNA test

• Not sequencing

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CF Detection Rates by Mutation Analysis (ACMG 23 mutation panel)

Group Incid Carrier Detect Risk After (-)

Ashkenazi 1/2300 1/24 94% 1/83,000

European 1/2500 1/25 88% 1/21,000

Hispanic 1/13,500 1/46 57% 1/18,000

African-Am 1/15,100 1/62 69% 1/54,000

Asian-Am 1/35,100 1/90 ~30% 1/75,000

Case: Fetal risk?

• Patient: Negative• Pre-test risk: 1/25-29

• After negative test: ~1/208

• Partner: No test• Risk of partner carrier status: 1/62 (pretest)

• Risk of affected fetus after mom’s (-) result:• (Mom) ½ x 1/208 x

• (Dad) ½ x 1/62 = 1 in 103,000

Fetal risk if Mom was POS?

• Patient: (+) ���� Refer

• Risk: 1/2

• Partner: (-)

• Pretest risk: 1/62

• After (-) test: 1/186

• Risk of affected fetus:

• (MOM) ½

• (DAD) ½ x 1/186 = 1 in 744

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Carrier Screening & Cystic Fibrosis

• Mutation analyses may reduce but do not eliminate the chance of having an affected child

• Mutations tested are those most frequently detected in disease (>0.1%)

• Frequencies of mutations vary in different ethnic/racial backgrounds

• Expanded panels – 23, 32, 35 (UCSF), 97 etc…

• Know about your laboratory’s panel

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Case 4

26 yo G1P0 at 10 weeks with a family history of a younger brother with cognitive disability who “looks different” than other family members. On further questioning her mother had early menopause.

• For which causes of cognitive deficiency is screening available?

• What is the risk to her fetus?

• What if her family history was negative?

Fragile X Syndrome• Heritable cognitive and developmental disability

• 1/3600 in males & 4,000-6000 females

• Males• 2nd most common form of cog impairment in males

• Varies – borderline to severe

• Behavior abnormalities, including autism• Anxiety, especially social anxiety• Unique cranio-facial characteristics

• Females• If affected, usually less severe• Premature ovarian failure • Cognitive abnormalities• Tremor ataxia

Fragile X – Who is at risk?• Family h/o Fragile X or

undiagnosed MR, autism

• Known maternal premutation or full mutation

• Women with h/o elevated FSH (<40 years) or ovarian failure of unknown etiology

• Family h/o premature ovarian failure, tremor/ataxia

• Women who request testing

• Those with intermediate alleles are not at risk of having an affected child

Fragile X Syndrome

• Fragile Site: Xp27.3

• Trinucleotide expansion (CGG)n• Normal (<44)

• Intermediate or “gray zone” (45-54)

• Pre mutation (55-199)

• Full mutation (>200)

• Meiosis expansion

• 56 repeats lowest known expansion to affected

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Fragile X – Carrier Rate

Pre & Full mutation ���� Fetus at risk

• Low risk women (negative family history)

• 1 in 113-549

• Suspicious family history

• 1 in 83

• Family history of Fragile X

• 1 in 4 (28.8%)

• History of premature ovarian failure

• 1 in 10

Risk of Expansion to Full Mutation

Category (CGG)n % to Full Mutation

Intermediate 55-59 (3.7%)

Premutation 60-69 (5.3%)

“” 70-79 (31.1%)

“” 80-89 (57.8%)

“” 90-99 (80.1%)

“” 100-200 (94-100%)

Fragile X – Universal Screening?

ACMG & ACOG: No population screening

• Complex inheritance

• Variation in phenotype in females

• Need for formal genetic counseling

• Difficult to understand complexities of testing

• But…reliable testing, severe phenotype, presumed cost effectiveness, desirability

• Thus, if formal counseling – offer Fra X?

Case 4

• 26 yo G1P0 at 18 weeks with a family history of a younger brother with mental retardation (MR) who “looks different” than other family members. On further questioning her mother had early menopause. The fetus is male on ultrasound

Frag X – CGG repeats 80, 23

• What causes of MR can we screen for? • Is her fetus at risk? -• What if her family history was negative?

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Case 5

• 32 yo woman at 16 weeks heard a story on the radio about spinal muscular atrophy and wants carrier screening. Family history is negative.

Should you offer testing?

How do you test?

Limitations of testing?

Spinal Muscular Atrophy (SMA)

• Autosomal recessive

• 2nd most common fatal AR disorder

• SMN1 (survival motor neuron) gene deletions

• SMN2 may influence severity of SMA

• Genetics complicated in 3-4%

• No features of SMA and two copies of SMA1 on one chromosome

• Parents not identified as a carrier

• 2% de novo deletion

Spinal Muscular Atrophy (SMA)

• Progressive muscle weakness and paralysis

• α motor neurons

• Type I (Werdnig-Hoffman) - most severe

• Death prior to 2 years (respiratory failure)

• Type II

• Type III

Spinal Muscular Atrophy (SMA)

• Universal screening?

• Disease is severe (in most cases)

• Limited treatment available

• Reliable testing

• High pan ethnic carrier frequency (1 in 40-60)

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Spinal Muscular Atrophy (SMA)

• ACMG vs. ACOG

• ACMG

• Offer routine carrier screening

• ACOG

• No routine screening

• Limitations in prediction of SMA type w/o Fam Hx

• No data on education, counseling, preferences, utility measurements, cost effectiveness

• False negative rate

Case 5

• 32 yo woman at 16 weeks heard a story on the radio about spinal muscular atrophy and wants carrier sceening. Family history is negative

Should you offer testing? - ?refer

How do you test? – SMN1 carrier screening

Limitations of testing? – false positive

Carrier screening

• Geographic ancestry vs. Universal

• Follow ACOG guidelines

• Capable of screen for Hgb, CF, Ashkenazi

• Educate – limitations of screening

• Patient preferences

• Admixture of your patient population

• Refer when needed – family history

• ?Fra X, SMA

References

Ashkenazi Jewish/Eastern European

1) Preconception and Prenatal Carrier Screening for Genetic Diseases in Individuals of Eastern European Jewish descent. ACOG Committee Opinion, No. 442. American College of Obstetricians and Gynecologists. Obstet Gynecol 2009;114:950-3.

2) Screening for Tay-Sachs disease. ACOG Committee Opinion, No. 318. American College of Obstetricians and Gynecologists. Obstet Gynecol 2005;106:893-4.

Monaghan KG, Feldman GL, Palomaki GE, et al. Technical standards and guidelines for reproductive screening in the Ashkenazi Jewish population. Genet Med 200810-57-72.

3)Gross SJ, Pletcher BA, Monaghan KG. Carrier screening in individuals of Ashkenazi Jewish descent. Genet Med 2008;10:54-6.

4) Kaback M, Lim-Steele J, Dabholkar D, et al. Tay-Sachs disease--carrier screening, prenatal diagnosis, and the molecular era. An international perspective, 1970 to 1993. The International TSD Data Collection Network. JAMA. 1993; 270: 2307–15.

5) Kaback MM, (Updated [May 19, 2006]). Hexosaminidase A Deficiency. In: GeneReviews at GeneTests: Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. 1997-2010. Available at http://www.genetests.org. Accessed [3/8/2010].

6) Norton ME. Genetic screening and counseling. Curr Opin Obstet Gynecol 20:157-63.

7) Musci TJ. Screening for Single Gene Genetic Disease. Gynecol Obstet Invest 2005;60:19-26.8) Andermann E, Scriver CR, Wolfe LS, Dansky L, Andermann F. Genetic variants of Tay-Sachs disease: Tay-Sachs disease and Sandhoff’s disease in French Canadians, juvenile Tay-Sachs disease in Lebanese Canadians, and a Tay-Sachs screening program in the French-Canadian population. Prog Clin Biol Res 1977;18:161–88.

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References

Hemoglobinopathies

9) Hemoglobinopathies in pregnancy. ACOG Practice Bulletin No. 78. American College of Obstetricians and Gynecologists. Obstet Gynecol 2007;109:229-237.

10) Chan LC, Ma SK, Chan AYY et, al. Should we screen for globin gene mutations in blood samples with mean corpuscular volume (MCV) greater than 80fL in areas with high prevalence of thalassemia? J Clin Pathol 2001;54:317-320.

11) Hartevld CL, Kleanthous M, Traeger_Synodinos J. Prenatal diagnosis of hemoglobin disorders: Present and future strategies. Clin Biochem 2009;42:1767-79.

12) Musci TJ. Screening for Single Gene Genetic Disease. Gynecol Obstet Invest 2005;60:19-26.

Cystic Fibrosis

13)Update on carrier screening for cystic fibrosis. ACOG Committee Opinion, No. 325. American College of Obstetricians and Gynecologists. Obstet Gynecol 2005;106:1465-68.

14) Watson MS, Cutting GR, Desnick RJ, et al. Cystic fibrosis population carrier screening: 2004 revision of the American College of Medical Genetics mutation panel.

15) Palomaki GE, FitzSimmons S, Haddow JE. Clinical sensitivity of prenatal screening for cystic fibrosis via CFTR carrier testing in a United States panethnic population. Genet Med 2004;6:405-14.

16) Norton ME. Genetic screening and counseling. Curr Opin Obstet Gynecol 20:157-63.

17) Musci TJ. Screening for Single Gene Genetic Disease. Gynecol Obstet Invest 2005;60:19-26.

18) Murray J, Cuckle H. Cystic fibrosis and fragile X Syndrome: The arguments for antenatal screening. Comb Chem High Through Screening 2001;4:265-72.

References

Fragile X

19) Carrier screening for Fragile X. ACOG Committee Opinion, No. 469. American College of Obstetricians and Gynecologists. Obstet Gynecol 2010;107:1008-10.

20) Sherman S, Pletcher BA, Driscoll DA. Fragile X syndrome: Diagnostic and carrier testing. ACMG Practice Guideline. Genet Med 2005;7:584-587.

21) Cronister A, teacher J, Rohlfs EM, Donnenfeld A, Hallam S. Prevalence and instability of Fragile X alleles. Obstet Gyencol 2008;111:596-601.

22) Fanos JH, Spangner KA, Musci TJ. Attitudes toward prenatal screening and testing for Fragile X. Genet Med 2006;8:129-33.

23) Murray J, Cuckle H. Cystic fibrosis and fragile X Syndrome: The arguments for antenatal screening. Comb Chem High Through Screening 2001;4:265-72.

24) Toledano-Alhadef H, Basel-Vanagaite L, Magal N, Davidov B, Ehrlich S, Drasinover V et, al. Fragile –X carrier screening and the prevalence of premutation and full mutation carriers in Israel. Am J Hum genet 2001;69:351-60.

25) Fernandez-Carvajal I, Posada BL, Pan R, Raske C, Hagerman PJ, Tassone F. Expansion of an FMR1 Grey-Zone allele toa full mutation in two generations. J Mol Diagn 2009;11:306-10.

26) McConkie-Rosell A, Abrams L, Finucane B, et, al. Recommendations from multidisciplinary focus groups on cascade testing and genetic counseling for Fragile-X related disorders. J Genet Couns 2007;16:593-606.

27) Saul RA, Tarleton JC. (Updated [August 5, 2008]). FMRI- related disorders. In: GeneReviews at GeneTests: Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. 1997-2010. Available at http://www.genetests.org. Accessed [3/8/2010].

28) Hill MK, Archibald AD, Cohen J, Metcalfe SA. A systematic review od populations screening for fragile X syndrome. Genet in Med 2010;12:396-410.

References

Spinal Muscular Atrophy

29) Spinal Muscular Atrophy. ACOG Committee Opinion, No. 432. American College of Obstetricians and Gynecologists. Obstet Gynecol 2009;113:1194-1196.

30) Prior TW. Carrier screening for spinal muscular atropy. ACMG Practice Guideline. Genet Med 2008;10:1-3.

31) Prior TW, Russman BS. (Updated [April 3, 2006]). Spinal Muscular Atrophy. In: GeneReviews at GeneTests: Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle.

1997-2010. Available at http://www.genetests.org. Accessed [3/8/2010].