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Reproduction Week 2 2018/19 > 9: Genetics I > Flashcards

9: Genetics I Flashcards

1
Q

If there is a family history of inherited disease or dodgy genetic/ultrasound results in pregnancy, who should a mother be referred to?

A

Clinical geneticist

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2
Q

Which genetic sampling techniques for pregnancy use samples from the

a) placenta

b) amniotic fluid

c) blood?

A

a) Chorionic villus biopsy

b) Amniocentesis

c) Foetal / maternal blood sampling

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3
Q

Which tissues are sampled by

a) chorionic villus biopsy
b) amniocentesis
c) maternal blood sampling?

A

a) Placenta

b) Amniotic fluid

c) Maternal AND foetal blood

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4
Q

At what point in gestation can you do a

a) chorionic villus biopsy
b) amniocentesis
c) maternal blood sample for foetal DNA?

A

a) Around 11 weeks

b) 16+ weeks

c) 8+ weeks

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5
Q

What type of genetic sample is also known as non-invasive pre-natal testing?

A

Maternal blood sample for foetal DNA

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6
Q

When is the earliest point in gestation at non-invasive pre-natal testing can be carried out?

A

8 weeks

Making it very useful compared to chorionic villus biopsy and amniocentesis, which are both invasive and can only be done later in gestation

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7
Q

What is the risk involved in chorionic villus biopsy?

A

Miscarriage

1-2% miscarriage rate

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8
Q

Cells obtained from a chorionic villus biopsy may show different genotypes from one another.

Why?

A

Placental mosaicism

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9
Q

Which genetic sampling method can be carried out from around 11 weeks gestation?

A

Chorionic villus biopsy

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10
Q

Which genetic sampling method can be carried out from 16 weeks gestation?

A

Amniocentesis

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11
Q

What is the problem with amniocentesis as a genetic sampling method?

A

Tissue quality can be poor

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12
Q

Which genetic sampling method can be carried out from 8 weeks gestation, making it the earliest sample which can be done?

A

Maternal blood sample for foetal DNA

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13
Q

Taking maternal blood for foetal DNA, or non-invasive pre-natal testing, is one of the earliest and most effective tests you can do.

What’s the problem with it at the moment?

A

Can only test for a limited number of genetic disorders

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14
Q

Which percentage of embryos have chromosomal abnormalities?

A

40%

But 40% of embryos don’t result in miscarriage, so repair mechanisms must exist

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15
Q

Which whole genome tests are commonly used pre-natally?

A

Array CGH

Foetal DNA from maternal blood

Next generation sequencing (NGS)

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16
Q

Array CGH is a whole genome test used to detect (balanced / unbalanced) chromosome mutations.

A

unbalanced mutations

17
Q

Which targeted tests are commonly used pre-natally?

A

Point mutation testing

Quantitative fluorescent PCR (QF-PCR)

18
Q

What is the definition of a mutation?

A

Genetic change which causes disease

19
Q

What is the definition of polymorphism?

A

Genetic change which doesn’t cause disease on its own

20
Q

How many polymorphisms does a person have on average?

A

3 million

21
Q

Apart from genetic testing, how else can foetal abnormalities be discovered before birth?

A

Ultrasound scan

22
Q

When are foetal ultrasound scans typically carried out?

A

12 weeks

20 weeks

To check for structural abnormalities suggestive of congenital disease

23
Q

What measurement, made on foetal ultrasound, indicates whether or not a child has Down’s syndrome?

A

Nuchal thickness

24
Q

What is nuchal thickness?

Which disease is it used to diagnose?

A

Thickness of the skin on the back of a foetus’s neck

Seen during foetal ultrasound

Down’s syndrome

25
Q

After seeing clear nuchal thickening on foetal ultrasound, which genetic test would you use to diagnose Down’s syndrome?

A

Array CGH

Remember it detects extra or missing chromosomes - trisomy 21

26
Q

Apart from array CGH, what other genetic test could you use to diagnose Down’s syndrome?

A

Maternal blood for foetal DNA

=> Karyotype (trisomy 21)

27
Q

What is NIPT?

A

Non-invasive pre-natal testing

The use of foetal DNA from a maternal blood sample to diagnose genetic disorders

28
Q

What percentage of maternal blood contains some foetal DNA?

A

10%

So not a huge amount to sample

29
Q

What is an advantage of chorionic villus biopsy or amniocentesis over NIPT?

A

Can test for a greater number of disorders

NIPT is currently limited to Down’s syndrome

30
Q

Which genetic disorder is commonly diagnosed using NIPT?

A

Down’s syndrome

Occasionally you can use it for other stuff like DMD

31
Q

Apart from diagnosing genetic disorders, what else can you use NIPT for?

A

Sex determination

Is it a boy or a girl?

32
Q

___ chromosome translocations are better than ___ ones.

A

Balanced is better than unbalanced

33
Q

In which case is an unbalanced translocation not as bad?

A

If it affects sex chromosomes

e.g Turner’s 45 XO, Klinefelter’s 47 XXY

These children are definitely symptomatic but not devastatingly so

34
Q

What is a Robertsonian translocation?

A

Some chromosomes are acrocentric i.e they only have one side, nothing after the centrosome

In a Robertsonian translocation, an acrocentric chromosome binds to the end of a normal chromosome

Producing an unbalanced translocation

35
Q

Robertsonian translocations increase your chances of inheriting what type of genetic disorder?

A

Trisomy

Three copies of the same chromosome (even with an acrocentric chromosome stuck on the end)

This is bad

36
Q

What does aneuploidy mean?

A

Too few chromosomes

Too many chromosomes

37
Q

How would array CGH appear in a patient with a balanced translocation?

A

Normal

Array CGH only detects unbalanced translocations

38
Q

What do

a) large

b) small

unbalanced translocations cause in a foetus?

A

a) Miscarriage

b) Developmental delay (severity ranging from mild to severe)

Reproduction Week 2 2018/19 (9 decks)

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