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TAS Genetics ✅ > Autosomal Aneuplodies ✅ > Flashcards

Autosomal Aneuplodies ✅ Flashcards

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Biology 101 flashcards
1
Q

What is true of most autosomal aneuploidies?

A

They are fatal in utero

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2
Q

Which autosomal aneuploidies are survivable to term?

A
  • Trisomy 13
  • Trisomy 18
  • Trisomy 21
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3
Q

What autosomal aneuploidy has the most favourable outcome?

A

21 (Down’s syndrome)

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4
Q

Why does trisomy 21 have the most favourable outcome?

A

Because chromosome 21 has fewer genes than other chromosomes

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5
Q

Why does chromosome 21 have fewer genes than other chromosomes?

A

It is short and has low gene density

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6
Q

What is trisomy 13 known as?

A

Patau syndrome

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7
Q

What % of babies with Patau syndrome die in the first month?

A

50%

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8
Q

What is the prognosis of babies that survive the first month with Patau syndrome?

A

Most die in the first year

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9
Q

What are the common features of Patau syndrome?

A
  • Polydactyly
  • Cardiac abnormalities
  • Midline abnormalities of the head and face
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10
Q

What midline abnormalities of the head and face are common in Patau syndrome?

A
  • Closely-spaced eyes, single central eye (cyclopia)
  • Midline cleft lip and palate
  • Holoprosencephaly
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11
Q

What is holoprosencephaly?

A

When brain does not divide properly into left and right hemispheres

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12
Q

What happens to most babies with Edwards syndrome?

A

They die within the first year of life

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13
Q

What happens to children who survive the first year of life with Edwards syndrome?

A

They make little developmental progress

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14
Q

What are the features of Edwards syndrome?

A
  • Dysmorphic features
  • Poor growth antenatally and postnatally
  • Small head
  • Cardiac and renal abnormalities
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15
Q

Describe the dysmorphic features of Edwards syndrome?

A

They may be subtle, and can include;

  • Ear anomalies
  • Clinodactyly
  • Overlapping fingers
  • Micrognathia
  • Rocker-bottom feet
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16
Q

Why is Downs syndrome an important condition?

A

It is the only autosomal trisomy frequently associated with survival into adulthood

17
Q

What is often a feature of Downs syndrome babies at birth?

A

They are often hypotonic

18
Q

What are the dysmorphic features of Downs syndrome?

A
  • Epicanthic folds
  • Upslanted palpebral fissures
  • Protruding tongue
  • Sandal gap
  • Brushfield’s spots in the iris
  • Single palmar crease
19
Q

What organ systems are often abnormal in Downs syndrome?

A
  • Cardiac

- Gastrointestinal

20
Q

What cardiac abnormalities are common in Downs syndrome?

A
  • Atrioventricular septal defect (AVSD)

- Ventricular septal defect (VSD)

21
Q

What GI abnormalities are common in Downs syndrome?

A
  • Duodenal atresia

- Hirschsprung’s disease

22
Q

How severe are the learning difficulties in Downs syndrome?

A

Mild to moderate

23
Q

Is behaviour problematic in Downs syndrome children?

A

Often is in older children

24
Q

What are the long-term problems associated with Downs syndrome?

A
  • Short stature
  • Obesity
  • Increased risk of leukaemia and solid tumours
  • Increased risk of Alzheimers
25
Q

What % of cases of Down’s syndrome is caused by non-disjunction?

A

95%

26
Q

What is the risk of recurrence of Down’s syndrome caused by non-disjunction?

A

1%, or the mother’s age related risk, whichever is higher

27
Q

What % of cases of Down’s syndrome are mosaic?

A

2%

28
Q

What is the recurrence rate of mosaic Down’s syndrome?

A

Low

29
Q

How does the presentation of mosaic Down’s syndrome differ from in other causes?

A

The phenotype is often milder

30
Q

What % of cases of Down’s syndrome are caused by an unbalanced Robertson translocation?

A

2%

31
Q

What are the types of Robertsonian translocations causing Down’s syndrome?

A
  • 14/21 or 21/22

- 21/21

32
Q

What is the risk of recurrence of Down’s syndrome in another child when the cause is a 14/21 or 21/22 Robertsonian translocation?

A

10% if the mother is carrying the translocation

2.5% if the father is carrying the translocation

33
Q

What is the risk of recurrence of Down’s syndrome in another child when the cause is a 21/21 translocation?

A

100%

34
Q

Why is there a higher risk of recurrence in another build when Down’s syndrome is caused by an unbalanced Robertsonian translocation?

A

Because parents may carry a balanced translocation, which can result in unbalanced transmission

35
Q

What it is important to differentiate between when determining the recurrence rate of Down’s syndrome?

A

Conventional trisomy 21 occurring as a result of non-disjunction from that caused by unbalanced Robertsonian translocation

36
Q

How can the genetic cause of Down’s syndrome be determined?

A

Karyotyping or FISH analysis

37
Q

How does karyotyping or FISH analysis determine the cause of Down’s syndrome?

A

By directly visualising the chromosomes

38
Q

What is not useful in determining the recurrence risk of Down’s syndrome?

A

Parental microarray
Ovarian function testing
Skin biopsy for chromosomal mosaicism
Clinical features

39
Q

Why is parental microarray not useful in determining the recurrence risk of Down’s syndrome?

A

It will not detect a balanced translocation

TAS Genetics ✅ (13 decks)

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