Genetics

Question 1

When is CVS done?

Answer 1

11.5 weeks

Question 2

When is amniocentesis done?

Answer 2

16 weeks+

Question 3

What is the miscarriage rate of CVS?

Answer 3

1 - 2 %

Question 4

What is the miscarriage rate of amniocentesis?

Answer 4

0.5 - 1%

Question 5

Where does the tissue come from in CVS? What are the potential problems with this?

Answer 5

Placenta. Risk that the condition could be confined to the placenta (placental mosaicism) or not in the placenta but present in the fetus.

Question 6

What are you analysing in amniocentesis?

Answer 6

Fetal skin/urine cells

Question 7

When can you test the fetal DNA from the maternal blood?

Answer 7

8 weeks +

Question 8

What are the indications for doing array CGH?

Answer 8

High risk of chromosomal trisomy on screening
Fetal abnormality on scanning
Parent has balanced chromosomal rearrangement

Question 9

List some genetic tests that assess the whole genome

Answer 9

Standard Karyotype
Array CGH
Quantification of fetal DNA in maternal serum
Whole genome sequencing

Question 10

List some targeted genetic tests

Answer 10

Point mutation testing
FISH
Quantitive Fluorescent PCR

Question 11

Describe the routine prenatal screening done in Scotland?

Answer 11

Dating US scan with serum biochemistry
Serum screening at around 16 weeks
20 week detailed scan to look for other fetal abnormalities

Question 12

What can we currently look for with non invasic pre natal testing (ie from the mothers blood)

Answer 12

Sex determination
Trisomy testing

Occasionally chromosome deletions or a single gene

Question 13

What is the best first line genetic test?

Answer 13

Array CGH

Question 14

What is a robertsonian translocation?

Answer 14

Once chromosome is stuck onto the and of another

Question 15

What are the risk of having a robertsonian translocation?

Answer 15

Trisomy is pregnancy

Question 16

What does array CGH look like in a person with a balanced translocation?

Answer 16

Normal: aCGH only detects imbalance.

Question 17

What are the HFEA guidelines on PGD?

Answer 17

Clinics must have a licence to carry out PGD

Each new condition tested for must be licensed by HFEA

Question 18

At what day in an embryo biopsy done to carry out PGD?

Answer 18

Day 3 (8 cell stage)

Question 19

What test do you do to carry out sex determination of an embryo? In what conditions would this be necessary?

Answer 19

FISH

X linked recessive conditions such as duchenne’s

Question 20

List some conditions in which PGD would be considered

Answer 20

Parental chromosome abnormality
X linked disorders
Single gene disorders eg CF, Huntingtons where there is a known family history