Cytogenetics y Genetic Screening
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| At what age do pregnant mothers start having an elevated risk of birth defects | maternal age 35 or greater >> increased risk for Down’s syndrome and other non-disjunctions
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| What are major indicators that their is an elevated risk of birth defect? | 1. maternal age 35 or greater 2. previous child with a de novo chromosomal abnormality 3. presence of a structural chromosomal abnormality in a parent 4. family history of a genetic disorder
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| What two techniques can be used to detect possibility of chromosomal disorder in low risk mothers | examination of maternal serum or ultrasound
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| What are the three invasive methods of obtaining cells fetal cells for analysis | amniocentesis, chorionic villus sampling , and percutaneous umbilical cord blood sampling
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| What is amniocentesis? | it is where a syringe is inserted through abdominal wall to remove 20-30 ml of amniotic fluid
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| When can an amniocentesis be performed? | week 16, because there is not enough amniotic fluid until week 16 gestational age
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| What types of cells would you find in amniotic fluid? | skin and lung cells
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| How is the amniotic fluid typically analyzed? | The cells (skin and lung) are isolated and cultured. The amniotic fluid itself is sometimes analyzed – ex. high levels of alpha–fetoprotein indicative of neural tube defects and other disorders
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| What are two major advantages of chorionic villus sampling over amniocentesis? | 1. cells from a chorionic villus sampling are already readily dividing so a karyotype can be done quickly without a culture (2) A chorionic villus sample can be taken earlier (10-12 weeks) than amniocentesis (16 weeks)
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| What are the two ways a chorionic villus sampling can take place? | biopsy needle can be inserted through either the abdominal wall or through vagina to obtain sample of chorionic villus
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| List the prenatal diagnosis techniques in order of risk from least risk to most risk | amniocentesis (lowest risk), chorionic villus, and percutaneous umbilical cord blood sampling (highest risk)
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| When can percutaneous umbilical cord blood sampling be preformed? | By week 20
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| Besides the actual technique how does percutaneou umbilical cord blood sampling differ from amnicentesis and chorionic villus samping? | It is rarely done solely for karyotyping purposes, though it gives access to white blood cells, the cell typically karyotype
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| What is genetic screening, and how does it differ from genetic testing? | genetic screening is a population based method for identifying persons with certain genotypes known to be associated with a genetic disease or predisposition to a genetic disease. It differs from genetic testing due to size of pop. testing < screening
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| What are some examples of things that are genetically screened for? | phenylketouria (all 50 states), galactosemia, congenital hypothyroidism (non-genetic) and sickle cell
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| What is the disease criteria for a screening program? | 1. high incidence in target pop. 2. serious effect on health 3. tratable or preventable
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| What is the criteria for tests utilized in a screening | 1. non-invasive and easily carried out 2. accurate and reliable 3. inexpensive
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| What is the criteria for a screening program? | 1. widespread and equitable availability 2. Voluntary participation 3. acceptable to the target population 4. full information and counselling provided
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| What is the only major proposal for adult genetic screening? | hemochromatosis ( autosomal recessive disorder cause by iron overload which leads to permanent organ damage). It is successfully treated by repeated phlebotomy, and tested by serum iron-transferrin levels
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| What is heterozygote screening? | tests for healthy individuals who are at risk for having affected children
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| What are somethings typically tested by way of heterozygote screening? | Tay Sachs disease among Jews of eastern European descent. (incidence lowered from 85% to 65% as a result) Beta–thalassemia in Cyprus (successful reduction of incidence) sickle cell in African Americans (no decrease in incidence)
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| What is typically tested for in a prenatal screening | Only standard screening in maternal serum is for alpha-fetoprotein (nuerotube defect) and fetal karyotyping with advanced maternal age (ex. trisomy 21 - down syndrome)
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