Genetic Screening: Amnio, Cvs And Rapid FISH

Question 1

Echogenic bowel is associated with what two conditions?

Answer 1

• Down syndrome

- Cystic fibrosis

Question 2

What ultrasound abnormalities are associated with trisomy 21?

Answer 2

• increased NT
• Echogenic bowel
• double bubble (duodenal atresia)
• choroid plexus cysts
• AVSD/VSD
• diaphragmatic hernia

Question 3

What ultrasound anomalies are associated with trisomy 13?

Answer 3

• increased NT
• polydactyly (post-axial)
• unilateral cleft lip
• VSD (not AVSD)

Question 4

What ultrasound anomalies are associated with trisomy 18?

Answer 4

• increased NT
• clenched fist
• talipes (club foot)
• micrognathia
• unilateral cleft lip
• choroid plexus cysts
• VSD (not AVSD)
• diaphragmatic hernia

Question 5

What are the current techniques used in prenatal diagnosis?

Answer 5

Current = invasive
- amino, cvs, fetal blood sampling
Future = non-invasive
- foetal cells in maternal circulation
- foetal DNA in maternal circulation
- PGD

Question 6

What are the advantages and disadvantages of an open culture system?

Answer 6

Advantages
- Cultures reported to grow more rapidly
- Final result available in shorter time
Disadvantages
- expensive incubators
- external supply of CO2 needed
- increased risk of infection/cross contamination
- incubator maintenance needed (due to corrosion)

Question 7

What are the advantages and disadvantages of a closed culture system?

Answer 7

Advantages
- less risk of infection or cross contamination (no incubator humidification)
- simple less expensive incubators
Disadvantages
- Cultures reported to grow less rapidly
- longer time to report

Question 8

What are the major differences between in situ vs flask/tube cultures?

Answer 8

• for in situ culture, cells grown on cover slips/slides vs. in flask/tube cultures where cells are attached to coated base of flask/tube
• for in situ harvesting, cells harvested while still attached to slide but for flask/tube cultures trypsin/edta is needed to detach cells from vessel surface

Question 9

What are the four different types of mosaicism?

Answer 9

• Genuine: affecting somatic and germ cells
• Pseudo: false mosaic diagnosis arising as tissue culture artefact
• Inter tissue: mosaicism restricted to some tissues
• Confined placental: restricted to placental tissue and not in the foetus (CVS)

Question 10

Diagnosis of Pallister Killian syndrome (tetrasomy 12p: supernumerary marker chr) can be confounded by what type of mosaicism?

Answer 10

Inter tissue mosaicism

• Peripheral blood samples: 0-2% abnormal cells
• Skin fibroblast cultures: 50-100% abnormal cells
• Amniocytes/bone marrow cultures: 100% abnormal cells

Question 11

What are the two stages involved in a CVS result system?

Answer 11

• Direct (cytotrophoblast): same day/24hr result = aneuploidy/large Chr anomaly
• Culture (mesenchyme core): 2-3 wk = small Chr anomalies

Question 12

What are the advantages of chronic villus sampling?

Answer 12

• True first trimester diagnosis
• Prompt molecular and cytogenetic studies possible
• Two stage result system (direct/culture)

Question 13

What are the disadvantages of chronic villus sampling?

Answer 13

• Skill required to perform technique safely
• False pos/false neg issues
• Mosaicism (CPM vs true fetal mosaicism) - requires follow up invasive testing
• trisomic rescue and UPD issues