Pre-natal Diagnosis

Question 1

What are the different type of Pre-natal Diagnosis?

Answer 1

• Amniocentesis
• Chorionic villus sampling
• Ultrasonography
• Maternal Serum Screening in first and second trimester
• Analysis of foetal DNA in maternal circulation (NIPS)

Question 2

What is Amniocentesis?

Answer 2

• A doctor inserts a needle through the abdominal wall in the amniotic fluid
• Approx. 15 weeks of pregnancy of later
• A sample of fluid is withdrawn for analysis
• The fluid contains cells that have been shed by the fetus
• These cells are grown in a laboratory so that the chromosomes in them can be analysed
• Enables doctors to measure the alpha-fetoprotein level in the amniotic fluid  more reliably indicates whether the fetus has a brain or spinal cord defect than does measurement of this level in the woman’s blood

Question 3

What is Chorionic Villus Sampling?

Answer 3

• Approx. 10 – 11 weeks  sample of chorionic villi (part of the placenta) is removed by one two methods
  1) Trans-cervical method, doctor inserts a thin, flexible tube (catheter) through the vagina and cervix into the placenta
  2) Trans-abdominal method, a doctor inserts a needle through the abdominal wall into the placenta. In both methods, a sample of the placenta is suctioned out with a syringe and analysed.

Question 4

What is Ultrasound?

Answer 4

Ultrasonography can do the following:

• Confirm the length of the pregnancy
• Locate the placenta
• Indicate whether the fetus is alive
• After the third month, detect certain obvious structural birth defects, including those of the brain, spinal cord, heart, kidneys, stomach, abdominal wall, and bones
• In the 2nd trimester, detect structural defects that tend to indicate an increased risk of a chromosomal abnormality in the fetus (targeted ultrasonography)

Question 5

What is Maternal serum screening in first & second trimester?

Answer 5

• Alpha-fetoprotein(AFP)→15 weeks→increased levels predict for neural tube defects
• Test has high sensitivity for spina bifida and anencephaly
• Low levels may predict for Down Syndrome

Question 6

What is Analysis of foetal DNA in maternal circulation (NIPS)?

Answer 6

• During pregnancy, small number of fetal cells cross the placental barrier→6 to 8 weeks
• Cells can be analysed by FISH or PCR
• However isolation of fetal cells from maternal blood can
be challenging
• Recent focus on cell-free DNA (cfDNA) released from trophoblasts that undergo cell death

Question 7

What are the different types of Post-Natal Diagnosis?

Answer 7

a) Newborn screening
b) Heterozygote screening
c) Presymptomatic diagnosis

Question 8

What is Heterozygote screening?

Answer 8

• Testing (at phenotype of genotype level) a target population to identify unaffected carriers of a disease gene
• Carriers can then be given information about risks and reproductive options

Question 9

What is Newborn screening?

Answer 9

• A neonatal blood screening test

* Blood is collected using a heel prick and spotted onto a test sheet to dry for later testing.

Question 10

What is Preimplantation Genetic Diagnosis (PGD)?

Answer 10

• Performed on preimplantation IVF embryos

* DNA from a single cell is tested for the presence of a disease gene

Question 11

What are type of Therapy for Genetic Disorders?

Answer 11

• Enzyme replacement therapy (ERT)

- Gene therapy

Question 12

What is Gene Therapy?

Answer 12

Copies of cloned gene to be transferred
• Delivery system • Virus
• Ability to identify target cells, in which normal gene will be expressed

Question 13

What is Enzyme Replacement Therapy (ERT)?

Answer 13

• Uses recombinant DNA 
          technology to produce
          human therapeutic 
          proteins
       • Treats symptoms of 
          disorder; not a cure

Question 14

What is Polar Body Genetic Analysis?

Answer 14

• Genetic testing occurs before fertilization
• Used in cases of heterozygous female carriers of X-linked disorders
• If the polar body contains a mutant allele, the egg must contain the normal allele