UNIT 3 GENETICS.pptx

UNIT 3 GENETICS.pptx

• 1.
  PRESENTED BY, PRAKRUTHI
• 2.
  Genetic testing isa type of medical test that identifies changes in genes, chromosomes, or proteins.  The results of a genetic test can confirm or rule out a suspected genetic condition or help determine a person’s chance of developing or passing on a genetic disorder.  Many genetic diseases can be diagnosed by a careful clinical history and examination of patient who has or is suspected to have a genetic disease.  Recent advances in medical genetics has made it possible to diagnose many of the genetic disorders when fetus is inside the uterus itself. GENETIC TESTING
• 3.
  Genetic testing isdefined 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. GENETIC TESTING Genetic testing is voluntary and it has both benefits and limitations. Genetic testing is different from the other tests done in clinical practice. Genetic test of the patient may also provide results for family members. It may open up ethical or psychological problems. Genetic counseling is important before advising for any test with genetic implications.
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  Testing to confirma clinical diagnosis: When a genetic disorder is suspected on physical characteristics or symptoms, genetic tests are required for either confirmation of genetic disease or to rule out a suspected genetic disorder. Carrier testing/screening: Carrier of particular genetic disorder is an unaffected individual who carries one copy of a mutated disease. Carrier testing is done in unaffected gene for a individuals who have a family history of a genetic disorder. Predictive and Pre-symptomatic testing: Pre-symptomatic testing is most commonly done for individuals, who have a family member with a genetic disorder, but are not having features of the disorder themselves at the time of testing..
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  Genetic testing beforea pregnancy is ideal, because this provides the wide range of choices if an increased risk of a deleterious genetic condition is detected.  Most of the genetic tests are done after the woman becomes pregnant.  Depending on the time of performing, these genetic tests, they can be divided into four types.  Preimplantation: Before conception (i.e. when one or two of the parents are carriers of a certain trait). Prenatal testing: These are done after conception. Newborn or neonatal, childhood screening. Screening tests in adolescence and adulthood.
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  It is alsoknown as embryo screening. It is performed to detect genetic changes in embryos prior to the implantation. This can reduce the risk of having a child with a particular genetic or chromosomal disorder. The human embryos can be produced using assisted reproductive techniques such as in-vitro fertilization (IVF). In vitro fertilization involves removing egg cells from a woman's ovaries and fertilizing them with sperms outside the body.
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  for fertilization (IVF): Oocytesare collected from mother's ovary by ultrasound guided technique. Oocyte is fertilized by husband's sperm by puncturing the oocyte. This is known as intracytoplasmic sperm injection (ICSI). The fertilized oocyte is cultured to grow up to 8-10 cell blastocyst stage. One cell is removed from this early embryo and the DNA is extracted from the cell. DNA or chromosomal analysis is performed for any genetic abnormalities. The embryo is implanted into the mother's uterus only if it is healthy and free of genetic defects/errors.
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   Prenatal diagnosticgenetic analysis tests are performed on fetus or embryo before it is born to detect changes in a fetus's genes or chromosomes.  The couples with an increased risk of having a baby with a genetic or chromosomal disorder are usually offered this type of testing during pregnancy.  Newborn and Child Screening: It is used to identify genetic disorders just after birth, so that it can be treated early in life.
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  Newborn and childhoodgenetic analysis NEWBORN WITH : Major birth defects Unusual (dysmorphic) facial features Suspicion of a metabolic disorder (e.g. phenylketonuria) Positive newborn screening test Congenital hypothyroidism Suspected aneuploidy (e.g. features of Down syndrome) unbalanced autosome (e.g. Prader-Willi syndrome) sex chromosomal abnormality (e.g. Turner syndrome) fragile-X syndrome CHILD WITH : Developmental delay and/or unexplained mental retardation Unusually tall or short stature, or growth delays Chromosomal abnormality
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  A mother ofadvanced age (>35 years) who has increased risk of trisomy’s . A parent Already having child with a chromosomal abnormality or birth defect or family history of birth defects who is a carrier of a translocation (balanced reciprocal or Robertsonian) or inversion who is a carrier of an X-linked genetic disorder Family History of Chromosomal abnormality Single-gene disorder Neural tube defects Congenital structural abnormalities Mental retardation A fetus with abnormalities detected by ultrasound A genetic disorder for which there is no satisfactory treatment Abnormal levels of AFP, BHCG, and estriol performed as quadruplet /triple test Parental consanguinity Recurrent spontaneous abortions/miscarriages Previous unexplained stillbirth Intake of certain medications or teratogens during pregnancy Maternal conditions such as diabetes, epilepsy, or alcoholism
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  The placenta, fetusand amniotic fluid are located with the help of the ultrasound. With or without local anesthesia a thin, hollow needle (22 gauge with a stylet) is inserted into the uterus through the abdomen. When the needle enters the amniotic sac patient may feel a sharp pain for few seconds. About 10-20 mL of the amniotic fluid is aspirated. The fluid is normally clear and yellow. Remove the needle and apply bandage at the skin puncture site. Monitor the fetal activity by ultrasound. The amniotic fluid is centrifuged to separate the cells. The cells are then cultured for further karyotyping studies and DNA studies. The fluid is subjected to various biochemical tests for the detection of substances like the a-fetoprotein, carcinoembryonic antigen and others.
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  It is aninvasive technique in which a piece of chorionic villus material of placenta is obtained. It is generally performed between 10 and 12 weeks of pregnancy. It is done either trans cervically with a flexible catheter passing through the vagina and cervix into the uterus or by a needle inserted through the abdomen (transabdominal puncture). Both the methods are performed under ultrasound guidance, and piece of developing placenta are obtained. The viability of fetus is checked before and after the procedure. Indications: It is indicated for the diagnosis of chromosomal disorders or various genetic conditions by DNA analysis. Advantages It can be performed during much earlier weeks of gestation than the amniocentesis. Results are usually ready within 1-2 weeks which permit earlier termination of pregnancy, if required. Earlier termination of pregnancy is safer than late pregnancy. More cells for study are obtained than amniocentesis. Disadvantages CVS is not routinely done because it carries a risk of miscarriage and other complications.
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  A non-invasive andharmless procedure. In this method, high frequency sound waves echo back from tissue interfaces, organs including the baby in the amniotic cavity and a picture is obtained. During pregnancy, it is usually used to confirm that pregnancy is viable, assess gestational age, localize the placenta, assess amniotic fluid volume and monitor fetal growth. Ultrasonography is required during amniocentesis, chorionic villus sampling and fetal blood sampling, and it provides evaluation of fetal anatomy during the second and third trimesters.
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  The blood fromumbilical vein is obtained by passing a fine needle through the mother's abdomen into the umbilical vein in the umbilical cord. The fetal blood obtained, is subjected to genetic testing. This procedure can be used for intrauterine blood transfusions and administration of drugs directly into the fetus.
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  visualization of thefetus in the uterus by a fiberoptic self-illuminated instrument. The fiberoptic scope is inserted into the amniotic cavity under local anesthesia. Fetoscopy is usually performed between 18-22 weeks of gestation.
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  Normally, few fetalblood cells enter the maternal circulation through the chorionic villa of the placenta.The fetal cells from maternal blood can be separated and analyzed for particular DNA sequence. Fluorescence in situ hybridization (FISH) is one of the techniques in which fetal cells can be analyzed for conditions such as trisomy and monosomy X. The disadvantage of this technique is that maternal blood may contain only few fetal cells. Measurement of maternal serum for four bio chemical substances namely a-fetoprotein (AFP), human chorionic gonadotropin (HCG), unconjugated estriol (uE3) and inhibin A (INH-A) is known as quadruple screen test. Formerly AFP, hCG and estriol tests were known as triple screen test. This is a non-invasive test and is usually done in the second trimester (between the 15 and 20 weeks) of pregnancy. It is not a diagnostic test. Positive test may only suggest that a mother is at a possible risk of carrying a fetus with a genetic disorder. More invasive but more accurate tests are amniocentesis and chorionic villous sampling.
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   Inhibin-A iselevated in the blood serum of women carrying fetuses with Down syndrome.  Low levels of AFP and abnormal levels of hCG and estriol may indicate that the developing fetus has trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome) or other chromosome abnormality.  A raised AFP level indicates the need for further investigation by amniocentesis or ultrasound scanning.  Estimation of maternal serum a-fetoprotein (AFP) concentration in the second trimester is valuable screening test for neural tube defects such as spina bifida or anencephaly. INDICATION FOR QUADRUPLE  Women aged 35 years or more  Women who had a viral infection during pregnancy  Women exposed to high levels of radiation  Women with diabetes and on insulin  Who has taken harmful medications or drugs during pregnancy  With a family history of birth defects