Genetics

Question 1

Which organ do you carry out chorionic villus biopsy on?

Answer 1

The placenta

Question 2

How could you test fetal skin cells/urine

Answer 2

Amniocentesis

Question 3

How could you sample fetal blood?

Answer 3

Fetal blood sampling

Question 4

When can you carry out CVS?

Answer 4

11.5 weeks

Question 5

When can you carry out amniocentesis?

Answer 5

15 weeks

Question 6

Earliest genetic test you can perform during pregnancy?

Answer 6

Fetal DNA from maternal blood (8 weeks +)

NO miscarriage risk!

Question 7

Only genetic test with NO miscarriage risk

Answer 7

Fetal DNA from maternal blood

Question 8

This test carries the risk of confined placental moscaicism

Answer 8

Chorionic villus biopsy

Question 9

What are single nucleotide polymorphisms?

Answer 9

Single base changes

Question 10

What are copy number variations?

Answer 10

Insertions or deletions of DNA segments

Question 11

If you have a high risk of trisomy on screening, which test would you do next?

Answer 11

Array cGH

Question 12

If you see a fetal abnoramlity on scanning, what test would you do next?

Answer 12

Array cGH

Question 13

If a parent has a balanced chromosomal rearrangement, what test should you do?

Answer 13

Array CGH

Question 14

Around what week could you see increased nuchal thickness?

Answer 14

Week 12

Question 15

What is covered in the week 12 pre-natal screening?

Answer 15

This scan dates gestation and looks at the serum biochemistry

• done at week 12
• increased nuchal thickness may be seen

Question 16

When is serum screening done and what does it look at?

Answer 16

• done week 16

- looks at maternal blood to look for biochem markers of Down syndrome

Question 17

What does the 20 week detailed scan look at?

Answer 17

To look for other fetal abnormalities

Question 18

What week could you check maternal blood for biochem markers of Down syndrome?

Answer 18

Week 16

Question 19

What can you use non-invasive prenatal testing to look for?

Answer 19

• sex determination
• trisomy testing

(occasionally: chromosome deletions or looking at a single gene)

Non-invasive testing = maternal blood with fetal DNA in it)

Question 20

A mother has a son with duchennes, what test can you offer?

Answer 20

Non-invasive prenatal testing to determine sex of the baby:

• if it is a boy do CVS (because X-linked)
• if it is a girl, reassure

Question 21

Mrs Green is 12 weeks pregnant – serum biochemistry and nuchal thickness measurement gives a risk of 1 in 40 that the baby is affected with Down syndrome. What test can you do?

Answer 21

So she’s already had the ultrasound
= do non-invasive prenatal testing
-test the mum’s blood for fetal DNA

Question 22

Mrs Blue comes to see you. She is 18 weeks pregnant. A detailed scan has shown that her baby has a cardiac defect: an AtrioVentricular Septal Defect that is commonly seen in Down syndrome.

Answer 22

Do amniocentesis and array CGH

-this is the best test for several reasons e.g. array CGH will detect small deletions such as 22q11 deletions

Question 23

Trisomy 13

Answer 23

Patau syndrome

Question 24

Patau syndrome

Answer 24

Tisomy 13

Question 25

Bilateral cleft lip and postaxial polydactyl

Often varying degrees of holoprosencephayl sometimes resulting in cyclopia

Answer 25

Patau syndrome (trisomy 13)

Question 26

What would array CGH look like in the parent with a balanced translocation?

Answer 26

aCGH would be normal (aCGH only detects imbalance)

Question 27

Mrs Roberts comes to see you. She is 10 weeks pregnant. She has a balanced reciprocal translocation between chromosome 4 and chromosome 9, that has a high risk of causing a liveborn child with multiple malformations.
What tests would you do?

Answer 27

• chorionic villus sample

- direct karyotype/FISH may be available

Question 28

When can you carry out a termination of pregnancy?

Answer 28

before 13 weeks = surgical
after 13 weeks = induction

There is no time limit for TOP if there is a risk of serious abnormality in the child or to the health of the mother