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POM GENETICS > Genetic Testing > Flashcards

Genetic Testing Flashcards

1
Q

What happens in a normal pregnancy?

A

Positive pregnancy test- no longer confirmed with GP
Book into antenatal care- see midwife
Nuchal scan- 10-14 weeks gestation (Ultrasound scan)
Mid-trimester anomaly scan- 20-22 weeks gestation (Ultrasound scan)

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2
Q

When is a nuchal scan done?

A

10-14 weeks gestation

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3
Q

What 5 things can a Nuchal Scan do?

A
  1. date the pregnancy
  2. diagnose multiple pregnancies
  3. disgnose major fetal abnormalities
  4. diagnose early miscarriage
  5. assess the risk of down syndrome
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4
Q

What technique is used to assess the risk of down syndrome?

A

Nuchal translucency scan

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5
Q

what is Nuchal translucency test?

A

Thickness of fluid at back of foetal neck.
Increased >3mm can indicate: chromosome abnormalities e.g., down syndrome, edwards, patau, turners
Usually combined with maternal blood markers and maternal age

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6
Q

At how many weeks is a mid trimester scan done?

A

20-22 weeks

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7
Q

What is the purpose of the mid trimester anomaly scan?

A

Look for structural anomalies especially specific organs like heart, brain, spinal cord, face, kidney and abdomen and to measure lengths of bones

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8
Q

When is prenatal testing offered? (5)

A

Following abnormal findings at nuchal scan or mid-trimester scan

Following results of combined test which give an increased risk of a chromosome abnormality

If previous pregnancy or child affected with a condition e.g., down syndrome, cystic fibrosis

If parent(s) carrier of chromosome rearrangement or genetic condition, e.g., t(13;14), DMD, HD

If there is a family history of genetic condition

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9
Q

If the nuchal thickness is >3mm, what 3 things can this indicate?

A
  1. Increased risk of down syndrome
  2. Birth defects
  3. Chromosomal abnormalities
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10
Q

What birth defects can arise from an increase nuchal translucency? (5)

A
  1. Cardiac abnormalities
  2. Pulmonary abnormalities
  3. Renal defects
  4. Abdominal wall defects
  5. Skeletal dysplasias
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11
Q

What is linked to nuchal translucency which increases the risk of the baby having down synrdome?

A

Maternal age

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12
Q

What type of test is a nuchal translucency scan?

A

A screening test (not diagnostic)

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13
Q

What are the 4 main aims of prenatal testing?

A
  1. Inform / prepare parents
  2. Allow for the termination of pregnancy if necessary
  3. To manage the remainder of the pregnancy
  4. To prepare for complications at or after birth
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14
Q

What type of scan is used to look at the fetal organs in more detail?

A

A fetal MRI

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15
Q

What serum markers are tested in maternal serum screening?

A

Serum markers for trisomy 18, 21 and neural tube defects

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16
Q

How do serum markers in the mothers blood for conditions like neural tube defects get there?

A

Leak from placenta into mothers blood

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17
Q

When is the 1st trimester maternal serum screening and NT measurement done at?

A

11-14 weeks

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18
Q

What is PAPP A?

A

Hormone made by placenta during pregnancy

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19
Q

What might a low PAPP A suggest?

A

Defective / smaller placenta

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20
Q

When are PAPP A levels measured?

A

11-14 weeks

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21
Q

What is measured during the 2nd trimester maternal serum screen?

A

AFP, UE3 and hCG

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22
Q

What is non-invasive prenatal diagnosis?

A

analysing the DNA fragments present in the maternal plasma during pregnancy (cell-free DNA)

Most of the DNA comes from the mother- 10-20% comes from the placenta, which is representative of the baby (cell free foetal DNA)

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23
Q

When is cffDNA first ever detectable?

A

4-5 weeks gestation

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24
Q

When is the Cell-Free Foetal DNA reading most accurate?

A

9 weeks

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25
Q

What do you need for non-invasive prenatal diagnosing?

A

Recessive conditions where the mother and father carry different mutations in the same gene
Cystic fibrosis (haplotyping- RHDO) can test for both maternal and paternal mutation

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26
Q

When is non-invasive prenatal diagnosing offered?

A

When there is an X-linked condition in the family e.g., DMD
The test detects SRY gene on Y chromosome, enabling us to determine if male or female foetus

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27
Q

Does cffDNA testing test for aneuploidy?

A

Yes, offered after high risk combined screen
Tests for T13, T18, T21

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28
Q

What are the limitations of NIPD and NIPT? (4)

A

Multiple pregnancies
Women with a high BMI
Women not prepared for implications
An invasive test may still be required to confirm an abnormal result

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29
Q

What are the benefits of NIPD and NIPT? (4)

A

The number of invasive tests carried out is likely to reduce as a result
There is no increased risk of miscarriage
Less expertise is required to perform a blood test than invasive test
In many cases we can offer NIPD/ NIPT earlier than traditional invasive testing, thereby getting a result much earlier

30
Q

What three conditions can you be pre-natally tested for for free on the NHS?

A
  1. Apert Syndrome
  2. Achondroplasia
  3. Thanatophoric dysplasia
31
Q

What gene is detected on the Y chromosome in sexting tests?

A

The SRY gene = males

32
Q

In what instance is sexting offered?

A

when there is an X-linked condition in the family - males more at risk so if the baby is male, then go on to pre natal tests to double check

33
Q

What are the two types of invasive tests required?

A

Amniocentesis and Chorionic Villus Sampling

34
Q

What is done to chorionic villus sampling and amniocentesis?

A

molecular, cytogenetic and biochemical testing is done on the samples

35
Q

Where are the chorionic villi found?

A

As part of the developing placenta

36
Q

Why is a sample of the chorionic villi taken?

A

It has the same DNA as foetus

37
Q

Why is CVS chosen over amniocentesis?

A

It allows the parents to have their results earlier than amnio

38
Q

When is CVS done?

A

11-14 weeks, usually at 12

39
Q

How are CVS samples taken?

A

Transvaginally or transabdominally

40
Q

What is the sample of chorionic villi?

A

Part of developing placenta- same DNA as foetus

41
Q

At what stage is amniocentesis done at?

A

from 16 weeks

42
Q

What are the risks of CVS?

A

1-2% risk of miscarriage
Infection
Resus sensitisation

43
Q

What does amniocentesis involve?

A

Sample of amniotic fluid is taken as it contains foetal cells

44
Q

What are the 3 risks associated with Amniocentesis?

A
  1. Rh sensitisation
  2. Miscarriage
  3. Infection
45
Q

What tests are done with the DNA sample?

A

Karyotype if chromosomal abnormality in family (results in 2 weeks)

QF-PCR (Quantitative fluorescent PCR) for all (looks for t13,18&21 and sex chromosomes) (results within 24-48 hours)

46
Q

What happens to cffDNA in women with a higher BMI?

A

Lower cffDNA count as they have more of their own DNA

47
Q

What is the limitation of non-invasive prenatal tests involving twins?

A

not possible to tell which foetus the DNA is from

48
Q

What is the purpose of a CGH array?

A

looks for imbalances in chromosomes that may lead to diseases (picks up microdeletions and duplications)

49
Q

What may be done after a CGH array if chromosomal imbalances are found?

A

Testing of parents to see if they are carriers

50
Q

When are CGH arrays offered?

A

If there are concerns on 20-week scan

51
Q

What happens if something is found on CGH array?

A

Test parents to see if either is a carrier- helps with interpretation

52
Q

How do you carry out a CGH array?

A
  1. Extract and label DNA (there is sample and control DNA in different fluorescent dyes)
  2. Hybridize and wash (mix and hybridize to a microarray printed with thousands of oligonucleotides probes then wash)
  3. Scan (detect colours of dye using a fluorescence scanner)
  4. Analyze data (compute and report gains or losses in the test DNA using software)
53
Q

What is a trio exome/ prenatal exome test?

A

A full genetic sequencing

54
Q

When are trio exome/ prenatal exome tests offered?

A

When previous pregnancies showed serious anomalies eg brain, skeletal, heart and dysmorphic features

55
Q

How long does it take for results of a prenatal exome test to come back?

A

urgent- 1 week

56
Q

What does the prenatal exome test use?

A

DNA from foetus and parents

57
Q

Is the prenatal exome test able to explain a baby’s features?

A

No or there may be an uncertain result

58
Q

What are the four potential options for reproduction? (you can just not have children)

A

Conceive naturally (no prenatal testing/ have prenatal testing)
Adopt
Use egg / sperm donors
Pre-Implantation Genetic Diagnosis - IVF

59
Q

when is pre-implantation genetic diagnosis used?

A

For conditions caused by single faulty gene to reduce the amount of non-embryo DNA (including sperm DNA) which could make the risk of a wrong diagnosis higher

60
Q

Are egg and sperm donations anonymous?

A

No, when they turn 18 they have the right to contact donor

61
Q

What is pre-implantation genetic diagnosis?

A

Uses IVF with an additional step to genetically test the embryo before implantation
PGD is particularly used by people who do not want TOP

62
Q

What are the stages of preimplantation genetic diagnosis?

A

Stimulation of the ovaries
Egg collection
Insemination
Fertilisation
Embryo biopsy
Embryo testing
Embryo transfer
Pregnancy test

63
Q

At what stage is the embryo biopsied?

A

8 cell stage (blastocyst)

64
Q

What is an intracytoplasmic sperm injection?

A

When a single sperm is injected into the center of each egg

65
Q

What are the downsides of PIGD?

A
  1. Can be emotionally stressful
  2. Lengthy and expensive process
  3. Success rate is low - around 30% per cycle
66
Q

why do patients have PGD?

A

translocation carriers, HD, DMD (only implant female embryos where mutation in family unknown), CF

67
Q

How many round f PIGD are couples usually funded for provided they fit the criteria?

A

1 baby or 3 cycles

68
Q

What are the eligibility criteria for PGD?

A

Female partner is under age of 39
Female partner has a BMI of 19-30
Both partners are non-smokers
Couples are 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 (at least 10%)

69
Q

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

A
  1. Arrange CVS and amniocentesis, PGD, cffDNA
  2. Give results
  3. Facilitate decision making
  4. give results of tests
  5. Discuss recurrence risks and plans for future pregnancies
  6. Arrange termination if necessary
70
Q

How do genetic counsellors facilitate decision making?

A

In the context of:

Previous experience
Family situation
Religion
Personal beliefs
Psychosocial situations
Balancing miscarriage risk with genetic risk
Dealing with indecision
Couples do not always agree

71
Q

Does cffDNA test for aneuploidy?

A

Yes, offered after high risk combined screen
Tests for T13, T18, T21

POM GENETICS (9 decks)

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