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MedGen (Personal) > Structural Rearrangements > Flashcards

Structural Rearrangements Flashcards

1
Q

Percent of structural abnormalities in patients with ID or autism

A

15-20%

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2
Q

Incidence of structural abnormalities (livebirths and conceptions)

A

1:400 livebirths, 1:200 conceptions

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3
Q

Structural abnormalities more likely to occur in maternal or paternal meiosis

A

paternal

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4
Q

Interstitial deletions percent

A

84% paternal

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5
Q

Terminal deletions percent

A

70% paternal

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6
Q

Duplications percent

A

58% paternal

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7
Q

Translocations percent

A

62% paternal

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8
Q

Reciprocal translocations percent

A

96% paternal

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9
Q

Robertsonian translocations are mostly maternal or paternal in origin

A

maternal

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10
Q

Recurrence risk for numerical abnormalities

A

1% in mid 30s

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11
Q

Recurrence risk for structural abnormalities

A

1-50%

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12
Q

Incidence of robertsonian translocation

A

1:1,000

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13
Q

Acrocentric chromosomes

A

13, 14, 15, 21, 22

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14
Q

Most common robertsonian translocation and percent

A

13;14 75-85%

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15
Q

Second most common type of robertsonian translocation and percent

A

14:21 8-10%

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16
Q

least common type of robertsonian translocation and what type of inheritance event

A

homologous and de novo

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17
Q

21;21 rob translocation is what risk

A

100%

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18
Q

Reciprocal translocation incidence

A

1:700-1:1000

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19
Q

Reciprocal translocation

A

exchange of genetic material between non-homologous chromosomes or at non-homologous sites

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20
Q

Percent of balanced reciprocal translocations that are inherited

A

70%

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21
Q

If reciprocal translocation is inherited, what is the risk

A

no increased risk

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22
Q

If reciprocal translocation is de novo, risk is

A

6-7%

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23
Q

Percent of reciprocal translocations that are de novo

A

30%

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24
Q

small distal segments lead to

A

small imbalances and large risks for clinically affected live born children

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25
Q

Large distal segments lead to

A

large imbalances and low risks for having live born abnormal children (high risks for miscarriages and period of infertility)

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26
Q

Partial trisomies compatiable with life

A

8, 9, 13, 18, 21, x, y

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27
Q

Partial monosomies that are compatible with life

A

4p, 5p, x, y

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28
Q

Empiric risk of unbalanced liveborn child with previous child with unbalance

A

20-25%

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29
Q

Empiric risk of unbalanced liveborn child with multiple miscarriages and no liveborn unbalanced individuals

A

2-4%

30
Q

Empiric risk of unbalanced liveborn child who was accidentally ascertained (ex: through amnio)

A

4-5%

31
Q

Factors that help drive reproductive risk for translocation

A

mode of ascertainment, size of exchanged segment, and chromosome regions involved

32
Q

Inversions

A

two-break intrachromosomal rearrangement in which material flips over or reverses orientation

33
Q

Percent of inversions that are inherited

A

80-90%

34
Q

Pericentric inversions

A

centromere is included between the two breakpoints

35
Q

Paracentric inversion

A

centromere is not between two breakpoints

36
Q

Duplication-deficiency recombinant chromosomes

A

odd number of crossovers that leads to loss of material

37
Q

Normal recombinant chromosomes

A

even number of crossovers, no net gain or loss of material

38
Q

The larger the inversion

A

higher risk for live born abnormal child
- have small distal segments, which produce small imbalances
- farther apart the breakpoints, the more likely crossovers will occur between them and form recombinant duplication/deficiency chromosomes

39
Q

Small inversions

A

less likely to be associated with live born abnormal child

40
Q

Empiric risk of pericentric inversion through abnormal child

A

5-15%

41
Q

Empiric risk of pericentric inversion if ascertained fortuitously through prenatal diagnosis

A

1%

42
Q

Types of chromosomes formed from paracentric inversions

A

dicentric and acentric

43
Q

Empiric risk of unbalanced offspring with paracentric inversion is

A

.1-.5%

44
Q

Insertions

A

3 break rearrangements where a piece of chromosomal material is excised from one location and inserted at a new location

45
Q

Incidence of insertions

A

1:80,000-1:10,000

46
Q

Intrachromosomal insertions

A

all 3 breaks within the same chromosome

47
Q

Interchromsomal insertions

A

break points in different chromosomes

48
Q

Empiric risk of intrachromosomal insertion in abnormal child

A

50%

49
Q

Empiric risk of interchromosomal insertion abnormal child

A

32-36%

50
Q

Ring chromosome

A

when a chromosome undergoes 2 breaks and the broken ends reunite in ring structure

51
Q

result from a ring chromosome that replaces normal chromosome

A

partial monosomy

52
Q

Result of a supernumerary ring chromosome

A

partial trisomy

53
Q

How are ring chromosome usually passed down

A

de novo

54
Q

incidence of ring chromosomes

A

1:27,225

55
Q

Most common ring chromosomes

A

13 and 18

56
Q

Typical phenotype of ring syndrome

A

severe growth restriction without major malformations, mild-moderate ID, minor anomalies

57
Q

Ring chromosomes are _________ during mitosis

A

unstable

58
Q

Dynamic mosaicism seen more commonly in what kind of rings

A

larger

59
Q

Percent of non-supernumerary rings that are inherited and by who

A

1% and mother

60
Q

Empiric risk of transmission of ring chromosome

A

40%

61
Q

Number of ring chromosome cases with severe phenotype

A

1:3

62
Q

Probability that parent is balanced carrier when child is balanced carrier Trisomy 21

A

50-60%

63
Q

Reproductive risk for balanced carriers of Trisomy 21

A

unbalanced offspring, miscarriages, UPD

64
Q

How do balanced translocation chromosomes pair during meiosis and types

A

quadrivalent formation in meiosis, alternate, adjacent 1, adjacent 2

65
Q

alternate 2:2 segregation forms

A

balanced offspring

66
Q

adjacent 1 segregation

A

second most likely type of segregation

67
Q

Adjacent 2 segregation is typically

A

lethal

68
Q

Inverted homologues form

A

inversion loops during meiosis I

69
Q

Offspring of parents who have recombinant imbalanced chromosomes are more likely to inherit what type of structural rearrangement

A

a balanced inversion

70
Q

Which of the following statements are true about rings

A

Rings are responsible for dynamic mosaicism which can cause variation in skin
pigmentation and growth reduction.

71
Q

A mother with a 46, XX karyotype and a father with a 45, XY, rob(14;21)(q10;10) karyotype plan to have a child together. They are worried about having a child with Down Syndrome. Which of the following gametes produced from the father would the child not have Trisomy 21 but still be a carrier for a Robertsonian translocation after fertilization, given that the mother gives a gamete with an independent chromosome 14 and an independent chromosome 21

A

A gamete with a derivative 14, 21 chromosome only

72
Q

Which of the following situations could not produce a gamete that could lead to a child with a partial or full trisomy

A

anaphase lag

MedGen (Personal) (12 decks)

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