Genetic testing


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Genetic testing

  1. 1. By:Ms. Shalini joshi ist year s.c.o.n. dehradun
  2. 2.  Definition of genetic testing  Purpose of genetic testing  Types of genetic testing  Basis of genetic testing  Prenatal diagnosis and screening  Common diagnostic test  Techniques for pathological examination  Ethical legal and psychosocial issue in genetic testing
  3. 3. Finding genetic disease in unborn child  Finding out if people carry genes for a disease and might pass it on to their children.  Screening embryos for disease.  Testing for genetic disease in adult before they cause symptoms.  Making a diagnosis in a person who has disease symptoms  Figuring out the type or dose of a medicine that is best for a certain person. 
  4. 4.  Genetic testing is defined as “examining a sample of blood or other body fluids or tissue for bio-chemical chromosomal, or genetic markers that indicate the presence or absence of genetic disease.
  5. 5. A genetic testing is analyzing a DNA to look for genetic alteration that may indicate an increased risk for developing a specific disease or disorder.  Or  It is also defined as type of medical test, identifies changes in chromosomes, genes or proteins.
  6. 6.  Carrier screening which involves identifying unaffected individuals who carry one copy for the disease to be expressed.  Pre implantation genetic diagnosis.  Pre natal diagnostic testing.  New  Pre born screening symptomatic testing for estimating the risk of adult onset cancer and alziemer’s disease
  7. 7.  Conformational diagnosis of a symptomatic individual.  Forensic or identity testing.  Pre symptomatic testing for predicting adult onset disorders such as Huntington’s chorea.  It allows the genetic disorder of vulnerabilities to inherited diseases.  It can be used to determine a child potentiality or person ancestry.
  8. 8.  Quantitative genetic research has built a strong case for the importance of genetic factor in many complex behavioural disorder and dimensions in the domains of psychopathology, personality and cognitive abilities.  The genetic basis of behavioural disorder has largely relied on a reductionist one gene one disorder (ONOD) approach in which a single gene is necessary and sufficient to develop a disorder.  In contrast a quantitative trait loci approach involves the search for multiple genes.
  9. 9. Managing the remaining weeks of the pregnancy  Determining the outcome of the pregnancy  Planning for possible complications with the birth process  Planning for problems that may occur in the newborn infant  Deciding whether to continue the pregnancy  Finding conditions that may affect future pregnancies. 
  10. 10.  This is a non-invasive procedure that is harmless to both the fetus and the mother.  The developing embryo can first be visualized at about 6 weeks gestation.  Recognition of the major internal organs and extremities to determine if any abnormality can best be accomplished between 16 to 20 weeks gestation.
  11. 11.  the size and position of the fetus,  the size and position of the placenta,   the amount of amniotic fluid, the appearance of fetal anatomy,
  12. 12. Abnormalities may not be detected until later in pregnancy, or may not be detected at all.  A good example of this is Down syndrome (trisomy 21) where the morphologic abnormalities are often not marked, 
  13. 13. This is an invasive procedure .  Amniocenteses are performed between 14 and 20 weeks gestation.  An ultrasound examination always precedes amniocentesis  In the third trimester of pregnancy, the amniotic fluid can be analyzed for determination of fetal lung maturity  amniotic fluid can be analyzed for lecithin:sphingomyelin (LS) ratio, and/or for phosphatidyl glycerol (PG). 
  14. 14. fetal loss (0.5%)  maternal Rh sensitization.  If oligohydramnios is present, then amniotic fluid cannot be obtained. 
  15. 15.  CVS can be safely performed between 9.5 and 12.5 weeks gestation.  In this procedure, a catheter is passed via the vagina through the cervix and into the uterus to the developing placenta under ultrasound guidance  The introduction of the catheter allows sampling of cells from the placental chorionic villi.  These cells can then be analyzed by variety of techniques. The most common test employed on cells obtained by CVS is chromosome analysis to determine the karyotype of the fetus.
  16. 16.  This is a new technique that makes use of the phenomenon of fetal blood cells gaining access to maternal circulation through the placental villi.  The fetal cells can be sorted out and analyzed by a variety of techniques to look for particular DNA sequences  Fluorescence in-situ hybridization (FISH) is one technique that can be applied to identify particular chromosomes of the fetal cells recovered from maternal blood and diagnose aneuploid condition such as the trisomies and monosomy X.
  17. 17. It is difficult to get many fetal blood cells.  There may not be enough to reliably determine anomalies of the fetal karyotype or assay for other abnormalities. 
  18. 18.  The developing fetus has two major blood proteinsalbumin and alpha-fetoprotein (AFP).  The MSAFP test can be utilized to determine the levels of AFP from the fetus  Ordinarily, only a small amount of AFP gains access to the amniotic fluid and crosses the placenta to mother's blood.
  19. 19.  When there is a neural tube defect in the fetus, Then there is a means for escape of more AFP into the amniotic fluid.  The AFP from the fetus will end up in maternal blood in higher amounts.  Neural tube defects include anencephaly and spina bifida . 
  20. 20.  This test is most commonly used as a test for pregnancy.  The beta-HCG can also be quantified in serum from maternal blood, and this can be useful early in pregnancy when threatened abortion or ectopic pregnancy suspected  because the amount of beta-HCG will be lower than expected.
  21. 21.  An elevated beta-HCG coupled with a decreased MSAFP suggests Down syndrome.  Very high levels of HCG suggest trophoblastic disease (molar pregnancy).  The absence of a fetus on ultrasonography along with an elevated HCG suggests a hydatidiform mole  The HCG level can be used to follow up treatment for molar pregnancy to make sure that no trophoblastic disease, such as a choriocarcinoma, persists.
  22. 22. The amount of estriol in maternal serum is dependent upon a viable fetus, a properly functioning placenta, and maternal well-being. substrate for estriol begins as dehydroepiandrosterone (DHEA) made by the fetal adrenal glands This is further metabolized in the placenta to estriol.
  23. 23. The estriol crosses to the maternal circulation and is excreted by the maternal kidney in urine or by the maternal liver in the bile  The measurement of serial estriol levels in the third trimester will give an indication of general well-being of the fetus  If the estriol level drops, then the fetus is threatened and delivery may be necessary emergently  Estriol tends to be lower when Down syndrome is present and when there is adrenal hypoplasia with anencephaly.
  24. 24.  Inhibin is secreted by the placenta and the corpus luteum.  Inhibin –A is associated with an increased risk of trisomy 21,  A high inhibin –A may be associated with a risk for preterm delivery.
  25. 25.  Low levels of PAPP-A as measured in maternal serum during the first trimester may be associated with fetal chromosomal anomalies including trisomies 13, 18, and 21  Low PAPP-A levels in the first trimester may predict an adverse pregnancy outcome, including a small for gestational age (SGA) baby or stillbirth. A high PAPP-A level may predict a large for gestational age (LGA) baby.
  26. 26.  Combining the maternal serum assays may aid in increasing the sensitivity and specificity of detection for fetal abnormalities.  The classic test is the triple screen for alpha-fetoprotein (MSAFP), beta-HCG, and estriol (uE3). The "quadruple screen" adds inhibin-A.
  27. 27.  It is useful in detecting gross fetal parts.  The pattern of gross abnormalities can often suggest a possible chromosomal abnormality or a syndrome.  Consultations are obtained with clinical geneticists to review the findings  Examination of the placenta is very important, because the reason for the fetal loss may be a placental problem
  28. 28.  Microscopic examination of the placenta is important Microscopy can aid in determination of gestational age (lung, kidney maturity), presence of infection, presence of neoplasia, or presence of "dysplasia" (abnormal organogenesis).
  29. 29.  Radiographic views are essential for analysis of the fetal skeleton.  Radiographs are useful for comparison with prenatal ultrasound, and help define anomalies when autopsy consent is limited  To determine sites to be examined microscopically.
  30. 30.  Skeletal anomalies (dwarfism, dysplasia, etc.)  Neural tube defects (anencephaly, spina bifida, etc.)  Osteogenesis imperfecta  Soft tissue changes (hydrops, hygroma, etc.)  Teratomas or other neoplasms  Growth retardation  Orientation and audit of fetal parts  Assessment of catheter or therapeutic device placement
  31. 31. Culture can aid in diagnosis or confirmation of congenital infections: T - toxoplasmosis  O - other, such as Listeria monocytogenes, group B streptococcus, syphilis  R - rubella  C - cytomegalovirus  H - herpes simplex or human immunodeficiency virus (HIV) 
  32. 32.  Tissues must be obtained as fresh as possible for culture and without contamination.  A useful procedure is to wash the tissue samples in sterile saline prior to placing them into cell culture media.  Tissues with the best culture for growth are those with the least maceration: placenta, lung, and diaphragm.  Obtaining tissue from more than one site can increase the yield by avoiding contamination or by detection of mosaicism.
  33. 33.  Patient need to sufficiently informed about the implication of genetic screening before they can provide informed consent.  The public view genetic with a sense of inevitability. However, a genetic condition alone may modify risks from environmental or life style factor. The voluntary nature of the screening process must be emphasized. 
  34. 34.  To reduce potential psychological distress, counseling should be available to provide information about genetic risk and explain choices regarding genetic testing and further management.  Support is needed for individuals who need to consider issue such as stigma disclosure to family members and confidentiality.
  35. 35.  Couple known to carry a recessive or dominance single gene defect or sex linked condition need counseling about their reproductive option. This may include prenatal diagnosis and possible pregnancy termination in the case of an affected fetus and pre-implantation genetic diagnosis.
  36. 36. The public’s understanding of genetic may be limited and can lead to sigma.   Misunderstanding of the genetic risk of developing disease can increase stigmatization. This may be around life expectancy, lifestyle choices, or decision about having children.  Identification of a genetic condition before birth raises issue of whether the parents wish to terminate the pregnancy. Some commentators have argues that the ability to only select perfect babies is a form of eugenesis.
  37. 37.  Confidentiality  Like other medical information, result from genetic testing are considered confidential, under normal practice, the doctor patient relationship protect against disclosure of genetic information.  However there is less clarity where relative wish to know the result of a family member’s genetic test, as it may have direct relevance for them.
  38. 38.  Another particular dilemma is the case of a pregnant woman wanting to know the result of a test taken by the baby’s father.  The storage of genetic screening data and registries of patients creates particular concern, given that the results may impact negatively on family members.
  39. 39.  Doctors face a dilemma when reporting the results of genetic screening. Standard medical practice is based on the principles that doctor’s should focus on their patient and that medical information should remain confidential.  It is unclear if doctors are ethically permitted to inform relatives in cases when the result of genetic test indicates real risk to their health.
  40. 40.  Doctors may also be faced with a decision about whether to persuade patient about the need to disclose their test result to relatives.  Although most professional bodies that disclosure should not be against the right of relatives have won priorities.
  41. 41.  The primary concerns among the public is the use of genetic information to delay access to health insurance or medical treatment.  Conversely health insurance claim right to access such data where it exist to avoid the moral hazards of patient with known condition taking out an insurance policy without disclosing this information.
  42. 42.       Dutta D. C. “ textbook of obstetrics” 6th edition, new central book agency (p) limited, 2009. Gangane S. D. “human genetics” 3rd edition, Elsevier publishers, 2010. Mandal Sanjay “ fundamentals of human genetics” 2nd edition, New Central B Book agency, Page no. 209-212. Perry, Lsowdermilk, “Maternity and women’s health care” 8th edition, mosby an affiliated by Elsevier page no. 67-69. Sharma, Kumar Suresh, “human genetics in nursing, 2nd edition, Jaypee Publishers, 2011 Dictionary – Oxford essential dictionary. For learners of English, oxford university press. 