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genetics testing Flashcards

1
Q

order of a normal p

A

Positive pregnancy test – no longer confirmed at GP

Book into antenatal care – see midwife

Nuchal scan – 10-14 weeks gestation. Different tests dependent upon NHS Trust e.g. nuchal translucency, combined test etc.

Mid-trimester anomaly scan

Ultrasound examination is
the main method for prenatal diagnosis of fetal abnormalities. All pregnant women should be offered routine ultrasound scans at 11-14 weeks and again at 20-22 weeks.

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2
Q

why is nuchal scan importnat

A

determine risk of genetic condition

hormone tested
measure back of baby neck
risk figure for down syndrome( 1 in 150 is higher is high risk)

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3
Q

Aims of the 12 week scan

A 
To date the pregnancy accurately. 
To diagnose multiple pregnancy.
To diagnose major fetal abnormalities. 
To diagnose early miscarriage. 
To assess the risks of Down Syndrome and other chromosomal abnormalities.
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4
Q

what do you take into account

A

Taking into account the maternal age, blood hormone levels, nuchal translucency thickness, nasal bone, blood flow through the fetal heart and fetal abnormalities.

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5
Q

Increased Nuchal Translucency (NT) of > 3mm can indicate:

A

Chromosome abnormalities
Birth defects: -
Skeletal dysplasias

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6
Q

what is Nuchal Translucency (NT)

A

Thickness of fluid at back of fetal neck

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7
Q

how is an increase in Thickness of fluid at back of fetal neck
shown

A

larger gap between surface and neck

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8
Q

When is prenatal testing arranged?

A

Following abnormal findings at nuchal scan or mid-trimester scan
Following results of combined test which give an increased risk of Down Syndrome
If previous pregnancy affected with a condition e.g. DS, CF
If parent(s) carrier of chromosome rearrangement or genetic condition, e.g. t(13;14), DMD, HD.
FH of genetic condition

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9
Q

Aims of Prenatal Testing

A

To inform and prepare parents for the birth of an affected baby
To allow in utero treatment
Manage the remainder of the pregnancy
To be prepared for complications at or after birth
To allow termination of an affected fetus

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10
Q

for a more detailed scan what can be offered

A

feotal mri

see organs more clearly

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11
Q

how to diagnose heart conditions

A

featol cradiac scan

look at baby blood flow through heart

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12
Q

can genetic testing be done through

A

Cell-free fetal DNA (cffDNA)

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13
Q

where is it

A

floughting aroound mother blood

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14
Q

why in blood

A

from the placenta

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15
Q

when is it first detectable

A

from about 4 -5 weeks’ gestation

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16
Q

when is it accuratyly detected

A

9 weeks

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17
Q

what is cfdna

A

short dna fragments

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18
Q

NIPD

A

non invasive pre nateal diagnoses

done through dna

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19
Q

what can it test NIPD for

A

Achondroplasia - testing is free
Thanatophoric dysplasia - testing is free
Apert syndrome- testing is free

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20
Q

what other catergy

and what it tests for

A

xing
Currently offered when there is a X-linked condition in the family
Test detects SRY gene on Y chromosome, enabling us to determine if male or female fetus

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21
Q

if male

A

prenatal testing

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22
Q

female

A

no invasive test

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23
Q

cffDNA testing for Aneuploidy

A

NIPT

non duagnistic but a test

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24
Q

Limitations of NIPD and NIPT

A

Multiple pregnancies - It is not possible to tell which fetus the DNA is from when carrying twins/triplets etc.

The relative proportion of cell-free fetal DNA is reduced in women with a high BMI as they have more of their own cell-free DNA.

Although it is just a blood test, it has the same implications as an invasive test.
Women may prepare themselves more for the implications of an invasive test result
Women must consider the consequences of the results. Do they want this information?

An invasive test may still be required to confirm an abnormal result.

25
Q

Benefits of NIPD and NIPT

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 an invasive test.

In many cases we can offer NIPD /NIPT earlier than traditional invasive testing, thereby getting a result much earlier.

26
Q

when is Invasive Tests

A

if a known risk

27
Q

what are teh Invasive Tests

A

Chorionic villus sampling (CVS)

Amniocentesis

28
Q

what is CVS

A

tissue from the placenta

29
Q

what is Amniocentesis

A

fluid from around developing baby

30
Q

when does CVS happen

A

11-14 weeks

31
Q

what is the risk of misccarige

A

1-2 percent

32
Q

how is it done

A

Transabdominal

or transv

33
Q

what sample do you take

A

Takes sample of chorionic villi – part of developing placenta – same DNA as fetus

34
Q

what is a good thing abourt cvs

A

Allows patient to have an earlier result than amnio - important for many patients re. TOP decision

35
Q

when is Amniocentesis done

A

From 16 weeks

36
Q

what sample is taken

A

Takes sample of amniotic fluid which contains fetal cells

37
Q

what is the risk of miscarriage

A

up to 1 percent

38
Q

other risks (2)

A

Infection

Rh sensitisation

39
Q

What tests are done with the DNA sample?

A

Test for the genetic disorder in question

Karyotype if chromosomal abnormality in family

40
Q

what happens to all the samples

A

QF-PCR for all:

41
Q

what does QF-PCR look for

A

for chromosmes 13, 18 & 21

maybe s chromosome if s chromosme disorder is suspected

42
Q

when is CGH array done

A

If there are concerns on 20 week scan the gold standard is to offer CGH array

43
Q

what does it look for

A

Looks for small/large imbalances in chromosomes (picks up microdeletions and duplications)

44
Q

are parents tested

A

If something found on array we standardly test parents to see if either is a carrier. This can help with interpretation

45
Q

what is teh function of trio exome

A

looks at exome of baby if there are significant anomalies

46
Q

what is an exome

A

is the coding region of the genome

47
Q

is dna taken from both fetis and parents

A

yes

48
Q

why parenst

A

to confirm whether they are carriers

49
Q

when would it happen

A

~20 weeks

50
Q

what are the options of if there is a known reeproduction 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)
51
Q

what is the 2 stages of adoption

A

Registration and checks

Assessment and approval

52
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
(termination of fetus)

53
Q

The process of PGD (8)

A 
Stimulation of the ovaries
Egg collection
Insemination
Fertilisation
5. Embryo biopsy
6. Embryo testing
7. Embryo transfer
8. Pregnancy test
54
Q

what is intracytoplasmic s injection ICSI

A

single s injected to the centre of each egg

55
Q

what stage is teh single cell taken away

for genetic condition testing

A

blastocysts

56
Q

You receive a referral for Becky, who is 17 and is 12 weeks pregnant. Her brother died two months ago from Duchenne Muscular Dystrophy.

  1. ) What information do you need?
  2. ) What are her options?
  3. ) What psychosocial issues might you anticipate?
A

1) if her brother had a confirmed genetic diagnosis
is it from the mother or from a new mutation
test becky for if she is a carrier for
2) tests preg, invasive test
do gender test, if boy then invasive
termination
3) guilt, if she wants a baby with same genetic condition as her borther

57
Q

You receive a referral for Madeleine. She is 41 and has had 2 previous terminations for Down Syndrome. She is 6 weeks pregnant.

  1. ) What information do you need?
  2. ) What are her options?
  3. ) What psychosocial issues might you anticipate?
A

1) confirm diagnosis
check that doen syndorme is casused by a full extra 21 chromosome- if yes then it may be age related risk

2) Invasive test or NIPT
3) nervous,

58
Q

You receive a referral for Mary. Mary’s husband carries a balanced translocation between chromosomes 1 and 12. This translocation has a 1% liveborn risk and an increased miscarriage risk. She has had 7 miscarriages and is now 11 weeks pregnant.

  1. ) What information do you need?
  2. ) What are her options?
  3. ) What psychosocial issues might you anticipate?
A

1) confrim partners translocatoin
2) tests
continue or invasive test
3) Maybe nerbous for invasive test

59
Q

Barbara has a son who has global developmental delay, ASD, dysmorphic features. He is age 4 and has no speech. She is 5 weeks pregnant

1) What information do you need?
2) What are her options?
3) What psychosocial issues do you anticipate?

A

1) son comes in for genetic review, may have a CDH array
see if genetic diagnosis
2) test in preg for conditions
3) guilt

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