genetic testing.ppt


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genetic testing.ppt

  1. 1. Birth Defects <ul><li>150,000 babies born each year with birth defects (3-5%) </li></ul><ul><li>Birth defect = abnormality of structure, function, or metabolism present at birth that results in a physical or mental disability or is fatal. </li></ul><ul><li>Birth defects are the leading cause of infant mortality. </li></ul>
  2. 2. The Quest for the Perfect Child <ul><li>Attempts to minimize birth defects </li></ul><ul><li>Women having fewer children, so each one counts </li></ul><ul><li>Women having children at older ages, so risk for defects increases </li></ul><ul><li>Lorber and Moore: Designer babies </li></ul><ul><li>Sex selection </li></ul><ul><li>Eugenics </li></ul><ul><li>What is normal? </li></ul>
  3. 3. Fetal Quality Control <ul><li>Strother Ratcliff </li></ul><ul><li>Required decisions </li></ul><ul><li>Pressures to make certain decisions </li></ul><ul><li>Physical intrusions </li></ul><ul><li>Alteration of pregnancy experience </li></ul><ul><li>Potential of loss of rights of mother as fetus gains rights </li></ul>
  4. 4. But… <ul><li>Think about how far can we go? </li></ul><ul><li>Which birth defects are unacceptable and which ones are tolerated? </li></ul><ul><li>Should we encourage a woman to abort a child with a certain defect? </li></ul>
  5. 5. What Causes Birth Defects? <ul><li>Genetic </li></ul><ul><li>Environmental </li></ul><ul><li>Causes of 60-70% of birth defects are unknown. </li></ul>
  6. 6. Genetic causes <ul><li>Single abnormal gene </li></ul><ul><li>Combination of genes </li></ul><ul><li>Number or structure of chromosomes </li></ul><ul><li>Missing or extra chromosome </li></ul>
  7. 7. Environmental Causes <ul><li>Drug or alcohol abuse </li></ul><ul><li>Exposure to medications (Accutane, thalidomide) </li></ul><ul><li>Infections </li></ul>
  8. 8. Multifactorial Inheritance <ul><li>Genes + environment </li></ul><ul><li>Cleft lip/palate </li></ul><ul><li>Club foot </li></ul><ul><li>Some heart defects </li></ul>
  9. 9. Diagnosing birth defects <ul><li>Prenatal genetic testing is available, although no test is 100% accurate. </li></ul><ul><li>Counseling parents about the risks and choices. </li></ul><ul><li>Choices </li></ul><ul><ul><li>Continue pregnancy and arrange treatment at the time of delivery </li></ul></ul><ul><ul><li>Fetal surgery </li></ul></ul><ul><ul><li>abortion </li></ul></ul>
  10. 10. Prenatal Genetic Testing <ul><li>Testing recommended if </li></ul><ul><ul><li>You are 35 or older when the baby is due </li></ul></ul><ul><ul><li>You have a family history of birth defects </li></ul></ul><ul><ul><li>You have a child with a birth defect </li></ul></ul><ul><ul><li>You have type 1 diabetes prior to your pregnancy </li></ul></ul>
  11. 11. The Type of Testing <ul><li>And what it can reveal depends on the weeks gestation of the pregnancy </li></ul><ul><li>Some are more invasive tests than others </li></ul><ul><li>Some depend on maternal blood samples, ultrasound, amniotic fluid, tissue samples </li></ul>
  12. 12. First trimester <ul><li>Between 11 th and 14 th weeks of pregnancy </li></ul><ul><li>Maternal blood test to detect increased risk of Down Syndrome. It detects levels of HCG (a hormone, human chorionic gonadotropin ) and </li></ul><ul><li>PAPP-A (pregnancy associated plasma protein a). </li></ul><ul><li>May detect heart defects or skeletal problems </li></ul><ul><li>Blood test combined with ultrasound—sound waves create an image of the baby. Measures region under the skin behind the baby’s neck. </li></ul>
  13. 13. First Trimester Screen <ul><li>At 11 th week, identifies 87% of babies with Down Syndrome. </li></ul><ul><li>At 13 th week, identifies only 82%. </li></ul><ul><li>False positives are possible, so women need more testing. </li></ul><ul><li>1 in 20 have positive result on these two tests during the first trimester. </li></ul><ul><li>Followup is usually CVS </li></ul>
  14. 14. CVS <ul><li>Chorionic villus sampling (9-14 weeks) </li></ul><ul><li>Sample of placenta is extracted and tested for genetic abnormalities. Results in 2-7 days </li></ul><ul><li>Ultrasound guided needle through uterus or catheter through cervix </li></ul><ul><li>Risk of miscarriage is 1% </li></ul><ul><li>Does not screen for open spine defects </li></ul><ul><li>Balance early diagnosis vs. increased risk </li></ul>
  15. 15. Quad Marker Screen <ul><li>Maternal blood screening weeks 15-20 of pregnancy to detect Down Syndrome and open spine disorders like Spina Bifida </li></ul><ul><ul><li>Alpha-fetoprotein </li></ul></ul><ul><ul><li>human chorionic gonadotropin </li></ul></ul><ul><ul><li>estriol </li></ul></ul><ul><ul><li>Inhibin-A—a hormone produced by placenta </li></ul></ul><ul><li>1 in 20 false positive rate </li></ul><ul><li>Usually do ultrasound and amnio </li></ul>
  16. 16. Amnio <ul><li>Amniocentesis (15-18 weeks) </li></ul><ul><li>Risks of fetal loss: 0.5% (1 in 200) when done prior to 24 th week </li></ul><ul><li>Sample of amniotic fluid is drawn from woman’s abdomen using ultrasound guidance </li></ul><ul><li>Results in 2 weeks </li></ul><ul><li>Also used at 36 weeks to check lung maturity </li></ul>
  17. 17. Bozzette Argues <ul><li>“Along with the ability for rapid and early detection of congenital and hereditary disorders comes a responsibility to provide information and emotional support for families faced with the reality of disease and disability.” </li></ul>
  18. 18. Bozzette <ul><li>“Many issues remain unanswered such as to whom genetic testing should be made available and how much of this technique should become routine in prenatal care.” </li></ul>
  19. 19. Age for genetic testing <ul><li>Keeps creeping down. </li></ul><ul><li>It used to be 35 and over </li></ul><ul><li>Now it is 25-30. </li></ul><ul><li>What are the implications? </li></ul>
  20. 20. Risks for Defects by Age <ul><li>Chance of carrying an abnormal child </li></ul><ul><ul><li>35 years old: 1 in 2,000 </li></ul></ul><ul><ul><li>39 years old: 1 in 100 </li></ul></ul><ul><ul><li>44 years old: 1 in 20 </li></ul></ul>