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REPRODUCTION & GYNAECOLOGY > Genetics > Flashcards

Genetics Flashcards

1
Q

How is Down’s syndrome screened for?

A
  • Nuchal Translucency (skin fold thickness behind neck)

- Blood serum markers in mother

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2
Q

Why is the nuchal translucency increased in babies with Down’s Syndrome?

A
  • indication that lymphatics are developing too slowly

=> gap is too large

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3
Q

How is invasive genetic testing done whilst the foetus is in utero?

A
  • need to test tissue with same genetic makeup as the baby

i. e. chorionic villus sampling of placenta OR amniocentesis

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4
Q

When can chorionic villus sampling and amniocentesis take place?

A

CVS - 11.5 weeks

Amniocentesis - 15 weeks

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5
Q

What is Non Invasive Prenatal Testing?

A

Taking mothers blood and testing for free foetal DNA

- this can get into mothers circulation via placenta

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6
Q

What can non-invasive prenatal testing look for?

A
  • sex of baby
  • trisomy

OCCASIONALLY

  • chromosome deletions
  • single gene transfers
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7
Q

What is meant by confined placental mosaicism?

A
  • trophoblasts divide quickly => develop more abnormalities than cells that go on to become blastocyst
    => Placenta may have chromosome abnormalities that the baby does NOT have
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8
Q

If NT, serum markers in the mothers blood and NIPT indicate a high risk of Trisomy 21, what is the percenatge risk of the baby having this condition?

A

99%+

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9
Q

How do geneticists test mothers blood in NIPT and confirm a high suspicion of trisomy 21?

A
  • count number of each chromosome i.e. 1,2,3 etc
  • Count number of chromosome 21
    => if out of proportion to number of other chromosomes, this would indicate T21
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10
Q

NIPT can also be used for what other genetic conditions?

A

T18 (Edward’s)
T13 (Patau’s)

Also Turners 45X and Kleinfelters 47XXY

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11
Q

What does NIPT reduce the risk of?

A

Miscarriage due to amniocentesis

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12
Q

Describe the appearance of a baby with Down’s Syndrome ?

A
  • short fingers
  • round face
  • large tongue
  • epicanthic folds
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13
Q

What are the benefits of an antenatal genetic screening test?

A
  • identify and treat early

- identify if other family members are at risk

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14
Q

Why is there a debate surrounding screening for Down’s Syndrome in pregnancy?

A
  • there is not additional benefit to treating early

- HOWEVER people do say that early termination option for mother may be a benefit to the child

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15
Q

Up to what gestation can a mother choose to terminate her baby who is at risk of down’s syndrome?

A

NO LIMIT

- if risk of serious abnormality to child or to health of the mother

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16
Q

WHat is anencephaly, and why is early diagnosis significant?

A
  • no brain/head development
  • baby MAY progress to full term (may be stillborn due to labour)
  • parents need to psychologically prepare for appearance and limited survival of baby
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17
Q

If a family do not wish to proceed with a termination after a difficult genetic diagnosis in their baby, what other option do they have?

A
  • carry baby to term

- organ donation

18
Q

How does a baby with T18 (Edward’s) appear, and how long do babies with this condition survive?

A
  • small baby with smal facial features

- life limited => many don’t survive for long after birth (virtually none within 1 year)

19
Q

Is Down’s Syndrome considered a “severe” genetic disease?

A
  • Not necessarily due to variable presentation
  • parents may not be equipped do deal with any of these

They can have:

  • cardiovascular disease
  • behaviour issues
  • low IQ requiring lots of support
  • multiple surgeries -> time in ICU
  • increased incidence of some cancers
20
Q

If a US scan indicates a hand abnormality, what must you be aware of?

A
  • is this part of another condition/syndrome?

- e.g. DiGeorge, Thrombocytopaenic Absent Radius etc

21
Q

What criteria do patients make a Termination of Pregnancy decision upon?

A
  • social/religious views
  • previous experience
  • perception of disease
22
Q

What is NIPT eventually going to be able to analyse?

A

Chromosome Karyotype

23
Q

What invasive genetic testing is carried out on the chorionic villus sample of on an amniocentesis sample?

A
  • Chromosome Microarray (1st Line)
  • Single Gene changes
    => PCR
    => Next Generation Sequencing
24
Q

What is the problem with chromosome microarray?

A

Cannot pick up balanced translocations

- only identifies EXTRA or MISSING genetic material

25
Q

What can Chromosome Microarray be used to identify?

A
  • Trisomy
  • Foetal Abnormalities
  • Unbalanced Translocations
26
Q

What is the disadvantage of PCR?

A
  • you need to know where to look within 30,000 genes
  • cannot sequence ENTIRE genome

e.g. if baby is thought to display Myasthenia Gravis symptoms, then this is an NMJ problem and all genes encoding for ACh can be tested

27
Q

Prenatal genetic testing allows the obstetrics team to decide on a high or low risk pathway for a baby’s delivery. TRUE/FALSE?

A

TRUE

28
Q

What is meant by a “floppy baby”?

A
  • lack of head control
  • low tone
  • baby lying flat
  • no resistance to movement
  • easily moved and fall out of grasp
29
Q

Where in the nervous system can a lesion cause a floppy baby?

A
  • cortex
  • spinal cord
  • anterior horn cells/motor neuron
  • NMJ
  • Muscles
30
Q

What problems in a baby’s cortex can cause a “floppy baby”?

A
  • Hypoxic Ischaemic Encephalopathy
  • Intracranial Haemorrhage
  • Cerebral Malformation
  • Chromosomal (T21, Prader-Willi)
  • Congenital infection (TORCH)
  • Acquired Infection
  • Peroxisomal disorders
  • Drugs (e.g. Benzodiazepines)
31
Q

What common congenital infections are outlined by the acronym TORCH?

A

TO - Toxoplasmosis
R - Rubella
C - CMV
H - Herpes, HIV, Hepatitis

32
Q

What damages the spinal cord and can cause a “floppy baby”?

A
  • Birth trauma (Breech)

- Syringomyelia (cysts in spinal cord - often causes “mermaid” looking baby => legs stuck together)

33
Q

What conditions due to damage or lesion of the anterior horn cells can cause a baby to appear floppy

A

Spinal Muscular Atrophy

34
Q

How would you determine that the cause of “floppy baby” was central rather than peripheral?

A
  • normal strength
  • normal or increased reflexes
    +/- seizures, dysmorphic features or decreased alertness
35
Q

What investigations would you consider if a “floppy baby” was presented?

A

Bloods

  • genetic
  • metabolic
  • congenital infection screen
  • Creatinine Kinase (increases if muscle breakdown)

Imaging

  • US
  • MRI

Neuro

  • EEG
  • EMG (only after 6 months of age)
36
Q

What early intervention can be offered if the disease causing “floppy baby” is picked up early?

A
  • Respiratory support (if breathing muscles struggling)
  • Feeding Support
  • Physio
  • OT
  • Parental Involvement
37
Q

If a family history does not highlight a dominant, recessive or X Linked pattern of genetic disease, does this mean that a baby’s condition has no genetic cause?

A

No

- May be a de novo mutation

38
Q

Why does consanguinity increase recessiveness of genetic disease?

A
  • people reproducing are from same genetic lineage therefore both are more likely to be carriers
39
Q

What disorders can be offered rapid testing after a floppy baby is noticed on examination, yet no abnormalities on Chromosome Microarray?

A
  • Myotonic dystrophy
  • Spinal Muscular Atrophy
  • Prader-Willi Syndrome
40
Q

What part of the genetic materia is sequenced using next generation sequencing?

A
  • dont need to sequence whole genome
  • only sequence exons (2-3%)
  • beware of polymorphisms which may not actually cause disease
41
Q

Give an example of a condition which can cause floppy baby but can now be treated?

A

Spinal Muscular Atrophy

  • genetic treatment is targeted at RNA to modify damaged mRNA
  • NNT = 1 or 2 => VERY EFFECTIVE
  • However, very expensive!

REPRODUCTION & GYNAECOLOGY (58 decks)

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