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Genetics > 5. Prenatal Diagnosis of Genetic Disease > Flashcards

5. Prenatal Diagnosis of Genetic Disease Flashcards

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1
Q

What are the scans offered for a normal pregnancy?

A

Nuchal scan: 10-14 weeks
Mid-trimester anomaly scan: 20 weeks
Offered ultrasound scans at 11-14 and 20-22 weeks

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2
Q

What is the main method for prenatal diagnosis of foetal defects?

A

Ultrasound

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3
Q

When is a nuchal scan offered and what is it used to determine?

A

12 weeks
Date pregnancy
Diagnose multiple pregnancies (twins/ triplets)
Major Foetal Abnormalities
Diagnose early miscarriage
Assess risks of Down Syndrome (DS) and other chromosomal abnormalities

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4
Q

What is considered an abnormal nuchal translucency and what would such a result suggest?

A

> 3mm
Indicates possibility of:
Chromosomal abnormalities
Birth defects

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5
Q

How is risk of downs syndrome assessed in nuchal scan?

A 
Look at thickness of NT
Assess: 
maternal age
hormone levels
nasal bone 
foetal abnormalities
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6
Q

What birth defects may be identified from nuchal translucency?

A 
Cardiac anomalies
Pulmonary defects (diaphragmatic hernia)
Renal defects
Abdominal wall defects
Skeletal dysplasia’s
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7
Q

Why must further tests be taken after nuchal translucency?

A

NT is a screening test

NT is NOT diagnostic

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8
Q

When is prenatal testing arranged?

A

After abnormal findings at nuchal/ mid-trimester scan
After results of combined test which give an increased risk of DS
If previous pregnancy affected with a condition e.g. DS
If parent(s) carrier of chromosome rearrangement or genetic condition, e.g. t(13;14), Duchenne Muscular Dystrophy, Huntingdon’s Disease
FH of genetic condition

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9
Q

What are the aims of prenatal testing?

A

Inform and prepare parents for the birth of an affected baby
Allow in utero treatment
Manage remainder of pregnancy
Be prepared for complications at or after birth
Allow termination of an affected fetus

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10
Q

What are the 3 types of prenatal testing and which test fall under each category?

A

Scanning (ultrasound, MRI)
Non- invasive (maternal serum screening, cell free foetal DNA)
Invasive (chorionic villus sampling, amniocentesis)

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11
Q

What can the early ultrasound test be used for?

A

Dating
Nuchal translucency
Nasal bone

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12
Q

What can the anomaly ultrasound test be used for?

A

Higher detail

Indications of abnormalities that might need treatment

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13
Q

When are MRI tests performed and what is the purpose?

A

20 weeks+

Show how brain and heart are developing- indicates need for test for CF

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14
Q

What does maternal serum screening test for?

A

maternal serum markers in blood to detect increased risk of fetal trisomy 21, trisomy 18 and/or neural tube defects
Looks at hormones in maternal serum

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15
Q

When is maternal serum screening done?

A

11-14 weeks AND 16-20 weeks

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16
Q

What is indicated if at the 12 week maternal serum screening hCG is high and PAPP A is low?

A

Down syndrome

17
Q

What does maternal serum screening look for?

A

11-14 weeks = presence of hCG and PAPP A

16-20 weeks = presence of hCG, PAPP A, AFP and uE3

18
Q

In what situation is cell-free foetal DNA testing offered?

A

Offered when there is a X-linked condition in the family e.g. DMD
Or privately via NHS

19
Q

What is cffDNA used to determine?

A

The sex of the baby
(looks for the presence of the SRY gene)
If male: go to prenatal test
If female: no invasive test required

20
Q

What is NIPD?

A

Non-invasive prenatal diagnosis

21
Q

How does NIPD work?

A

Analyses DNA fragments present in maternal plasma during pregnancy (cell-free DNA).

22
Q

What are the limitations of NIPD and NIPT?

A

Multiple pregnancies – can’t tell which foetus DNA is from
High BMI – relative proportions of cffDNA is reduced in obese women
Ethical issues: may not prepare themselves for same implications as an invasive test
Invasive test may be required to confirm result

23
Q

What are the benefits of NIPD and NIPT?

A

No increased risk of miscarriage
Reduces the need for more invasive testing
Less expertise required than for invasive test
Can offer testing earlier than invasive methods

24
Q

When is invasive testing offered?

A

Offered if there is ‘known risk’

most accurate diagnosis, not just indication

25
Q

What is the problem with invasive prenatal testing?

A

Small risk of miscarriage

26
Q

What is Chorionic villus sampling (CVS) and when is it done?

A

Take a sample from the chorionic villi (part of developing placenta) which has the same DNA as the foetus
11-14 weeks

27
Q

What are the 2 approaches of CVS?

A

Transabdominal

Transvaginal

28
Q

What is amniocentesis and when is it done?

A

Taking a sample of amniotic fluid which contains foetal cells
16+ weeks

29
Q

What are the risks of amniocentesis?

A

Up to 1% risk of miscarriage
Infection
Rh sensitisation

30
Q

What tests are done to the DNA obtained via CVS or amniocentesis?

A

Karyotype if chromosomal abnormality in family

QF-PCR (test for trisomies) for all

31
Q

Speed of results from karyotype and QF-PCR tests

A

Karyotype: 2 weeks

QF-PCR: 24-48 hours

32
Q

What are the options for family planning for those with known reproductive risk?

A 
Conceive naturally, no prenatal testing
Conceive naturally, have prenatal testing
Use of egg and/or sperm donors
Adoption
Choose not to have children
Pre-implantation genetic diagnosis (PGD)
33
Q

Rules surrounding egg/ sperm donation

A

No longer anonymous

Strict medical, ethical and legal standards

34
Q

2 stages of adoption

A

Registration and checks: medical/ criminal background

Assessment and approval: home visits and panel review

35
Q

Describe pre-implantation genetic diagnosis.

A

IVF is used to produce a zygote
A cell is sampled at the 8-cell stage and tested to identify any genetic defects
Only the cells with no genetic defects will be implanted

36
Q

What are the eligibility criteria for PGD?

A

Female partner < age 39
Female partner BMI of 19-30
Both partners non-smokers
Couple living together in a stable relationship
No living unaffected children from the relationship
Known risk of having a child affected by a ‘serious’ genetic condition (>10%)
Female partner has hormone levels that suggest she will respond to treatment
An accurate genetic test is available
No welfare concerns for unborn child
A licence is required from HFEA for each genetic condition or indication
3 rounds funded

37
Q

Difficulties of PGD

A

Emotional and physical implications
Can be lengthy process
Success rates ~30% per cycle

38
Q

Name 5 genetic disorders PGD is used for

A 
Translocation carriers
HD
DMD- only implant female embryos
CF
BRCA1/2
39
Q

What is the role of a genetic counsellor in prenatal testing?

A

Arrange and explain tests
Facilitate decision making for individual circumstance
Give results
See patients following diagnosis in utero
Arrange termination
Discuss risks and plans for future pregnancies

Genetics (7 decks)

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