Chromosome Structural Abnormalities Flashcards

1
Q

Pallister Killian syndrome is caused by ?

A

Isochromosome 12p (tetrasomy 12p mosaicism)

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2
Q

_______ rearrangements/breakpoints occur in unrelated families

A

Recurrent

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3
Q

__________rearrangements/breakpoints occur in families

A

random

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4
Q

The ___________ is the first person in the family to have the rearrangement (balanced or unbalanced)

A

proband

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5
Q

Of all rearrangements, ______________ are the most common

A

translocations (txl)

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6
Q

________% of the population has a translocation

A

0.1% (to 0.14%)

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7
Q

Balanced de novo translocations have a ______% risk of symptoms

A

6-9%

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8
Q

Balanced de novo translocations (1 in 500) occur in meiosis ___________ of _____________ (gamete)

A

meiosis I
sperm

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9
Q

Three tests for translocations

A

karyotype (3-5 MB)
FISH
CMA (200 KB to 20 KB)

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10
Q

Chromosomes for Robertsonian translocations

A

13, 14, 15, 21, 22 and Y

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11
Q

There are two types of translocations.
1. ____________ in which two ends of chromosomes exchange segments.
2. ____________ exchange of p arms of acrocentric chromosomes.

A
  1. Reciprocal
  2. Robertsonian
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12
Q

___________ structure is where the homologs of the translocated chromosomes all try to pair in meiosis I

A

Tetravalent

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13
Q

In translocations and quadrivalent structures during meiosis I, __________ segregation leads to balanced chromosomes while ______________ segregation leads to unbalanced chromosomes

A

alternate
adjacent

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14
Q

First recognized recurrent translocation in humans

A

t(11;22)(q23.3;q11.2) -

47 chroms, 3:1 segregation = Emmanuel syndrome

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15
Q

t(11;22)(q23.3;q11.2) with 3:1 segregation (Chr 11, Chr 22, der(22))

A

Emmanuel syndrome

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16
Q

Emmanuel syndrome phenotype

A

ID
Heart defects
Failure to thrive
Malformations

17
Q

Two types of inversions

A
  1. Pericentric (with centromere)
  2. Paracentric (same chromosome arm)
18
Q

A _________ inversion involves the centromere

A

Pericentric

19
Q

Pericentric inversions occur in ____________

A

meiosis I

20
Q

Risk of having viable unbalanced embryo with pericentric inversion: ______ to ______%

A

5-15%

21
Q

Chromosomes which tolerate pericentric inversion

A

13, 18, 21

21
Q

Name for syndrome with pericentric, inv(8)(p23.1q22.1)?
rec(8)dup(8q)inv(8)(p23.1q22.1)

A

San Luis Valley syndrome
Dup(q)/Del(p)

22
Q

San Luis Valley syndrome phenotype?

A

*Heart defects
Tetralogy of Fallot, conotruncal defects, septal defects
*Dysmorphic facial features
Hypertelorism, abnormal dentition, abnormal hair whorl, wide face
*Intellectual disability

23
Q

Paracentric inversions have a risk of livebirth with recombinant of 0.1-0.5% due to ___________ segregation and recombination issues

A

meiosis I (U-loop better than than classic inversion loop crossover)

24
Q

Ring chromosomes usually occur__ _______ and are supernumerary chromosomes (47) but can be stable and inherited

A

de novo

25
Q

Ring chromosome phenotype (generic)

A

Growth restriction
Mild-Moderate Intellectual Disabilities
Minor dysmorphic features
Infertility

26
Q

Ring chromosome formation mechanism

A

Both ends of chromosome are deleted

27
Q

Incidence of ring chromosomes in live birth

A

1 in 30,000-60,000

28
Q

Isochromosomes form with loss of 2p arms and formation of two linked q arms. Name two examples.

A
  1. Pallister Killian (mosaic 12p tetrasomy)
  2. Variant Turner syndrome (Xq)
29
Q

_____% of protein-coding genes are dosage sensitive (haploinsufficient or triplosensistive)

A

17%

30
Q

Most reciprocal translocations, inversions, rings, etc. are unique (__________) to the proband/family in which it was found

A

random

31
Q

The mechanism for rearrangements involves _________ sequences

A

repetitive
(Alu, LINES, SINES, low copy repeats, dups etc.)

32
Q

______________ is the mechanism underlying most RECURRENT structural rearrangements

A

NAHR = non-allelic homologous recombination (repetitive sequences between genes)

33
Q

______________ is the mechanism underlying most NON-RECURRENT structural rearrangements

A

Non-homologous end joining (NHEJ)
*method for repairing double strands breaks