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What s New in Prenatal Genetic Screening

Genetics in Medicine. Human Genome Project has brought inherited health factors to the forefrontGenetic risk assessment, screening and testing are now part of primary careAre you ready?. Objectives. List the elements of prenatal genetic risk assessmentDiscuss the expanding role of ethnicity-based

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What s New in Prenatal Genetic Screening

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    1. What’s New in Prenatal Genetic Screening? Pamela M. Williams MD Dept of Family Medicine USUHS

    2. Genetics in Medicine Human Genome Project has brought inherited health factors to the forefront Genetic risk assessment, screening and testing are now part of primary care Are you ready?

    3. Objectives List the elements of prenatal genetic risk assessment Discuss the expanding role of ethnicity-based genetic screening Describe current options for screening for fetal chromosomal abnormalities

    4. Reproductive Genetic Risk Assessment May occur as part of preconception or prenatal care 4 key assessment areas Maternal age Family medical history Current pregnancy history Ethnic background

    5. Risk Assessment: Maternal Age Risk for chromosome abnormalities increases with maternal age Age establishes a priori risk

    6. EBM Recommendation # 1 Women at high risk for fetal aneuploidy (age > 35 at time of delivery or prior child/fetus with aneuploidy) should be offered genetic counseling Source: DoD/VA Uncomplicated Pregnancy Guideline Strength of evidence: B

    7. EBM Recommendation Update “Screening & invasive diagnostic testing for aneuploidy should be available to all women who present for prenatal care before 20 wks of gestation regardless of age” Source: ACOG Practice Bulletin #77 (1/07) Strength of evidence: B

    8. Risk Assessment: Family Medical History If a family history of a diagnosed genetic condition or birth defect is identified, referral for genetic counseling is appropriate Examples Prior child with spina bifida Niece with cystic fibrosis Nephew with Duchenne Muscular Dystorphy Brother with Fragile X syndrome

    9. Family Medical History For a non-specific, but concerning history, referral for counseling is also appropriate Examples Close family member with mental retardation of unknown etiology Multiple family members with “kidney disease” Previous child with seizure disorder and developmental delay

    10. Risk Assessment: Pregnancy History During a pregnancy, any reported exposures or maternal condition may prompt genetic counseling referral Known / potential teratogens Accutane Seizure medications Lithium Coumadin “Street drugs” Other: High fever Viral infections Maternal Diabetes

    11. Risk Assessment: Ethnic background

    12. Ethnicity-Based Carrier Screening Purpose: To detect couples at risk for prenatally diagnosable genetic disease Tests offered: based on ethnic background Should be offered to patients Seeking preconception counseling or Seeking infertility care or In first or early second trimester of pregnancy

    13. Carrier Frequencies Based on Ethnic Origin

    14. Principles of Counseling Pre-screening, counseling should include: Purpose, voluntary nature Range of symptoms/severity of each disease Risk of carrier status & affect on offspring Meaning of positive and negative results Factors to consider in decision-making Further testing necessary for prenatal diagnosis

    15. Case Study: CF Screening ACMG (American College of Medical Genetics) Published laboratory standards and guidelines for population-based CF screening ACOG ( American College of Obstetrics and Gynecology) Fall 2001, updated Dec 2005 Recommended offering or making available CF screening to preconception or prenatal patients

    16. 2005 ACOG Guidelines Information about screening should be “made available” to all couples Screening should be “offered” to Individuals with a family history of CF Reproductive partners of individuals with CF Couples in whom one or both are Caucasian and are planning pregnancy or seeking prenatal care Universal offering of screening is an option

    17. CF Carrier Screening Carrier frequency 1/25 to 1/29 in Caucasian & Ashkenazi Jewish populations Screening by DNA mutation analysis Pan-ethnic panel including all mutations with an allele frequency of at least 0.1% Current panel: 23 mutations Sequential vs. concurrent screening

    18. Interpreting the Results Risk estimation Directly related to ancestry Sensitivity is a function of number of mutations searched for in the panel Negative screen does not mean no risk Remaining risk=Residual risk An ability to present to patients information regarding the risk of being carriers and what that risk means for their planned or ongoing pregnancy is critical to a “successful” prenatal screening program. The “result” of this test is a risk assessment of each individuals risk of carrying a mutation on one copy of a gene. Any individual has a risk of being a carrier that is directly related to their ethnicity. Further, sensitivity of carrier testing is a function of the number of mutations searched for and the individual’s ethnicity. Even when a screen is negative, there remains some chance that an individual still carries a copy of the CFTR mutation. The remaining risk (the results of the test) is called the residual risk. RESIDUAL RISK NEVER EQUEALS ZERO because the recommended laboratory panel of mutations has an ethnic-specific sensitivity that never reaches 100%. On the opposite end of the spectrum, if both partners have a positive test result, it is still not certain that the child will have CF. Instead, the risk is 1:4 or 25%. Thus, the goal of screening is to inform patients of their individual residual risk, establish a residual risk of a conception affected with CF and subsequently inform patients of their options when the risk is sufficiently high. (next step chorionic villus sampling; amniocentesis—exact risk may be determined by these invasive methods) Confused? Let’s look at an example.An ability to present to patients information regarding the risk of being carriers and what that risk means for their planned or ongoing pregnancy is critical to a “successful” prenatal screening program. The “result” of this test is a risk assessment of each individuals risk of carrying a mutation on one copy of a gene. Any individual has a risk of being a carrier that is directly related to their ethnicity. Further, sensitivity of carrier testing is a function of the number of mutations searched for and the individual’s ethnicity. Even when a screen is negative, there remains some chance that an individual still carries a copy of the CFTR mutation. The remaining risk (the results of the test) is called the residual risk. RESIDUAL RISK NEVER EQUEALS ZERO because the recommended laboratory panel of mutations has an ethnic-specific sensitivity that never reaches 100%. On the opposite end of the spectrum, if both partners have a positive test result, it is still not certain that the child will have CF. Instead, the risk is 1:4 or 25%. Thus, the goal of screening is to inform patients of their individual residual risk, establish a residual risk of a conception affected with CF and subsequently inform patients of their options when the risk is sufficiently high. (next step chorionic villus sampling; amniocentesis—exact risk may be determined by these invasive methods) Confused? Let’s look at an example.

    19. Carrier Rates Pre/Post Testing

    20. Pitfalls in Screening All mutations are not tested Screening assumes properly identified paternity Residual risk estimates assume no family history Genotype-phenotype correlation cannot be assumed

    21. Dealing with Positive Results For the individual identified as a carrier: Recommend testing of father of baby ASAP Consider offering genetic counseling For the couple who are both positive: Chance of having an affected baby 1 in 4 Prompt referral for genetic counseling with discussion of prenatal testing Don’t fret: <1% of at risk couples will screen positive. For the individual identified as a carrier: Recommend testing of father of baby ASAP Consider offering genetic counseling For the couple who are both positive: Chance of having an affected baby 1 in 4 Prompt referral for genetic counseling with discussion of prenatal testing which includes mutation analysis of fetal cells obtained by chorionic villus sampling (10 wks EGA) or amniocentesis (15-18 wks EGA) Don’t fret: <1% of at risk couples will screen positive. For the individual identified as a carrier: Recommend testing of father of baby ASAP Consider offering genetic counseling For the couple who are both positive: Chance of having an affected baby 1 in 4 Prompt referral for genetic counseling with discussion of prenatal testing which includes mutation analysis of fetal cells obtained by chorionic villus sampling (10 wks EGA) or amniocentesis (15-18 wks EGA)

    22. Screening for Fetal Chromosomal Abnormalities Don’t fret: <1% of at risk couples will screen positive. For the individual identified as a carrier: Recommend testing of father of baby ASAP Consider offering genetic counseling For the couple who are both positive: Chance of having an affected baby 1 in 4 Prompt referral for genetic counseling with discussion of prenatal testing which includes mutation analysis of fetal cells obtained by chorionic villus sampling (10 wks EGA) or amniocentesis (15-18 wks EGA) Don’t fret: <1% of at risk couples will screen positive. For the individual identified as a carrier: Recommend testing of father of baby ASAP Consider offering genetic counseling For the couple who are both positive: Chance of having an affected baby 1 in 4 Prompt referral for genetic counseling with discussion of prenatal testing which includes mutation analysis of fetal cells obtained by chorionic villus sampling (10 wks EGA) or amniocentesis (15-18 wks EGA)

    23. Screening Option Explosion First trimester Second Trimester Integrative Sequential

    24. First Trimester NT (Nuchal translucency) PAPP-A (pregnancy associated plasma protein-A) hCG (human chorionic gonadotropin)

    25. Nuchal Translucency Timing: 11-14 wks EGA NT measurement > 3. 5 mm associated with increased risk of Chromosomal abnormalities Structural anomalies SAB, SGA, stillbirth Down syndrome detection rate 64-70%

    26. 1st Trimester Serum Screening Timing: EGA 9 to 13+6 wks Analytes used (with maternal age) hCG or Free b-hCG PAPP-A Detection rates with 5% screen positive rate Trisomy 21: 68 % Trisomy 18: 90%

    27. Combined: 1st Trimester Serum + NT Timing: 11-14 wks gestation NT best visualized @ CRL = 45-84 mm NT + maternal serum analytes Detection rates w/ 5% screen positive rate

    28. 1st Trimester Serum + NT Screen Pros Fingerstick dry blood is easy to collect Results available earlier in gestation Higher detection rates than 2nd trimester More accurate for multiple gestations Cons Requires certified ultrasonographer Does not screen for NTDs

    29. Second Trimester Options Triple screen Quadruple screen Genetic sonogram Extended sonogram: serum + ultrasound markers

    30. Quad Screen Analytes used (with maternal age) Alpha-fetoprotein (AFP) Unconjugated estriol (uE3) Beta-human chorionic gonadotropin (b-HCG) Dimeric inhibin-A Detection rates w/ 5% screen positive rate Trisomy 21: 75-80% (vs 60-70 % with triple screen) Trisomy 18: 60 % NTD: 75-80 %

    31. Genetic Ultrasound Fetal anatomy screen Timing: 18-20 wks Evaluate for major structural anomalies and minor markers for aneuploidy Conflicting views surround use as independent or adjunct screening test

    32. Integrative Testing Nondisclosure of 1st-trimester results Options Integrated (NT, PAPP-A, quad screen) Serum integrated (PAPP-A, quad screen) Down syndrome detection rates Integrated 94-96%* Serum integrated 85-88%*

    33. Sequential Testing Disclosure of 1st-trimester results Independent Step-wise…first-trimester test: Positive: diagnostic testing offered Negative: second trimester offered, then final combined risk determined Contingent..first-trimester test Positive: diagnostic test offered Negative: no further testing Intermediate: second trimester offered; combined risk determined

    34. Sequential Testing Detection Rates Independent 94-98% False positive rates higher! (11-17%) Not recommended. Step-wise sequential 95% Contingent 88-94 %

    35. ACOG 2007 Practice Bulletin #77

    36. Reminder! “Screening & invasive diagnostic testing for aneuploidy should be available to all women who present for prenatal care before 20 wks of gestation regardless of age. Women should be counseled regarding the differences between screening and invasive diagnostic testing.”

    37. Updated ACOG Recommendations (Level A) Combined 1st trimester screening is an effective screening test, better than NT alone Women with positive first trimester screens should be offered counseling and an option of CVS or 2nd trimester amniocentesis Training/standardization need for NT Neural tube screening should be offered to all women who elect first trimester aneuploidy screening

    38. Updated ACOG Recommendations (Level B ) Integrated 1st + 2nd screening is more sensitive than first trimester screening alone Serum integrated (1st) screening is a viable option if NT is unavailable Abnormal second trimester U/S warrants counseling & offer of diagnostic procedure Patients with > NT but negative aneuploidy screen should be offered targeted U/S and fetal echocardiogram

    39. Factors Impacting Choice Gestational age at first visit Number of fetuses Prior obstetric history Family history Availability of NT Test sensitivity Test limitations Risk of invasive procedures Desire for early test results Options for earlier termination $$$

    40. Practical Application Identify tests available in your area NT CVS Identify which tests will meet the needs of your patients Obtain materials to allow patients to make an informed decision Learn how to interpret and counsel risk assessment

    41. Take Home Points Screening protocols are complex and evolving rapidly The “best test” may differ from patient to patient Education is key…both for patients and providers

    42. Questions?

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