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MFM > Cytogenetics and Chromosomal Basis of Disease > Flashcards

Cytogenetics and Chromosomal Basis of Disease Flashcards

1
Q

what is cytogenetics

A

study of chromosomes and their abnormalities

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2
Q

% occurrence of chromosomal abnormalities?

A

1/150 live births

50% of 1st trimester and 20% of 2nd semester spontaneous abortions

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3
Q

how to do karyotype?

A
  1. collect living tissue (blood)
  2. culture for 48-72 hours
  3. induce arrest at metaphase because the chromosomes are most condensed
  4. fix and stain
  5. photograph
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4
Q

what is metacentric

A

the chromosomal arms (p and q) are roughly the same length

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5
Q

what is submetacentraic

A

chromosome arms (centromere) is off center (skewed toward one end)

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6
Q

what is acrocentric

A

centromere is near end of chromosome

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7
Q

which arm is p arm

A

short arm (petite)

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8
Q

which arm is q arm

A

long arm

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9
Q

staining techniques for chromosome staining

A
  1. G banding
  2. Q banding
  3. R banding
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10
Q

how to G band

A

Giemsa stain, bands are determined on base composition of G-C base

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11
Q

how to Q band

A

quinacrine mustard, seen via fluoroscence microscopy, correspond to G banding

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12
Q

how to R band

A

chromosomes are heat treated before staining, the bands are reverse from G and Q banding

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13
Q

why are different techniques used for chromosome staining

A

to see different views of chromosomes

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14
Q

what exactly is stained in karyogram/karyotypes

A

T lymphocytes in metaphase are fixed and stained

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15
Q

how are karyotypes looked at

A

fluorescence in situ hybridization (FISH), where DNA probes/complementary DNA sequences labeled with fluorescent tags. the probe binds the sequence looking for on chromosome.

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16
Q

what is best seen in FISH?

A

chromosomal rearrangements, copy number, and how many alleles of that particular gene there are in a cell (deletions, duplications), fusions

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17
Q

what is spectral karyotype

A

expansion of FISH where each chromosome is labeled with a different colored probe (greater resolution and can see more details)

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18
Q

benefits of spectral karyotype

A

can detect small chromosome rearrangements

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19
Q

what is comparative genomic hybridization and array CG?

A
  1. DNA probes are bound to the array that represent portions of the genome (loci and telomeres)
  2. microarray is exposed to labeled patient and control DNA
  3. sample is analyzed for differences in copy number for each probe in comparison to the control
    * basically, 2 different samples with different dyes and mix them. ID the gene looking at, see if more or less or same amount.
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20
Q

what can you see with comparative genomic hybridization?

A

increased or decreased number of copies of gene of interest. (something absent or extra)

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21
Q

what can you NOT see with comparative genomic hybridization?

A

balanced abnormalities - aka balanced translocation because test relies on difference in genetic content in numbers between patient and normal

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22
Q

how many chromosomes for haploid

A

23

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23
Q

how many chromosomes diploid

A

46

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24
Q

what is polyploid??

A

multiples of 23 – 69 or 92 chromosomes

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25
Q

characterize triploidy

A

usually undergo spontaneous abortion, but can survive birth; fetus has problems associated with placenta

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26
Q

what causes triploidy?

A

2 sperm fertilizing 1 egg – dispermy

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27
Q

what causes tetraploidy?

A

failure to complete early mitotic divisions in zygote, don’t survive long after birth

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28
Q

what is aneuploidy?

A

abnormal amount of chromosomes but NOT a multiple of 23 – not a true set of chromosomes, can contain extra chromosome or missing a chromosome

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29
Q

what causes aneuploidy?

A

nondisjunction during anaphase I or II during meiosis or anaphase of mitosis

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30
Q

what is monosomy?

A

there is only 1 copy of a particular chromosome in the zygote

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31
Q

which is the ONLY VIABLE FORM OF MONOSOMY

A

X chromosome monosomy

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32
Q

what is trisomy

A

3 copies of a particular chromosome in the zygote, most nonviable

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33
Q

which are the only 3 trisomy conditions that are viable?

A

13, 18, 21

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34
Q

what is nondisjunction of chromosomes?

A

mis-segregation of chromosomes during anaphase

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35
Q

what causes nondisjunction ?

A

failure of chromosomes to separate or lack of microtubule connections to one kinetochore

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36
Q

result of nondisjunction?

A

aneuploidy in resulting daughter cells

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37
Q

when does nondisjunction usually occur?

A

meiosis I

less common in meiosis II

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38
Q

what is trisomy 21?

A

down syndrome, most common autosomal trisomy in live births

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39
Q

characteristics of downs syndrome

A
  1. intellectual disabilities
  2. GI tract obstruction
  3. congenital heart defects
  4. respiratory infections
  5. predisposition for leukemia and alzheimers
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40
Q

what is trisomy 18?

A

Edwards syndrome, 2nd most common autosomal trisomy

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41
Q

survival rate of Edwards syndrome?

A

50% die within the first few weeks of life, less than 10% survive past 1 year

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42
Q

characteristic of Edwards syndrome?

A
  1. prenatal growth deficiency
  2. congenital heart defects
  3. low survival rate
  4. intellectual disability
  5. low set ears, rotated backward
  6. small mouth and chin
  7. rounded plantar surface – rocker bottom feet
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43
Q

what is trisomy 13?

A

patau syndrome

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44
Q

survival rate of Patau syndrome?

A

very low, less than 10% survive 1st year of life

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45
Q

characteristics Patau syndrome

A
  1. cleft lip/palate
  2. micropthalmia (small, abnormally formed eyes)
  3. cardiac defects
  4. polydactyly
46
Q

diseases nondisjunction of sex chromosomes

A
  1. Turner syndrome
  2. trisomy X
  3. Klienefelter syndrome
  4. XYY syndrome
47
Q

what causes Turner syndrome?

A

monosomy of the X chromosome

48
Q

karyotype of Turner syndrome

A

45, X

49
Q

characteristic of Turner syndrome?

A
  1. short stature
  2. broad, shield like chest
  3. webbed neck
  4. gonadal dysgenesis (absence of normal ovaries)
  5. congenital heart defects
50
Q

who is affected with Turner syndrome?

A

ALL AFFECTED ARE FEMALE

51
Q

who is affected with Klinefelter syndrome?

A

males

52
Q

karyotype of Klinefelter syndrome?

A

47XXY

53
Q

what is the most frequent aneuploidy of sex chromosomes?

A

Klienefelter syndrome

54
Q

when is Klinefelter syndrome detected?

A

after puberty

55
Q

characteristics of Klinefelter syndrome?

A
  1. tall and thin stature, disproportionately long arms and legs
  2. hypogonadism and low Testosterone
  3. underdeveloped secondary sex characteristics
  4. gynecomastia
  5. infertility
56
Q

characteristics of trisomy of x chromosme?

A

XXX karyotype, affected by females but they usually don’t show abnormal phenotype.

57
Q

possible characteristics of trisomy of X?

A

sterility, menstrual irregularity, mild intellectual delay, taller than average

58
Q

characteristics of 47,XYY syndrome

A

affected are taller than average males with slightly lower than normal IQ, increased risk of minor behavior disorders, hyperactivity, ADD, and learning disabilities.

59
Q

types of chromosomal abnormalities?

A
  1. chromosomal translocations
  2. chromosome deletions
  3. chromosome duplication
  4. chromosome inversion
60
Q

what causes chromosomal translocations?

A

breakage of 2 nonhomologous chromosomes, and exchange of the broken fragments

61
Q

what are balanced chromosomal translocations?

A

rearrangement doesn’t produce a loss or gain of chromosome material,

62
Q

type of balanced translocation

A

reciprocal translocation, where genetic material of 2 difference chromosomes is mutually exchanged

63
Q

phenotype of reciprocal translocation

A

no phenotype associated, because no loss of gain of chromosomes; gametes from person with reciprocal translocation can yield offspring with unbalanced translocation

64
Q

what are unbalanced chromosomal translocations?

A

rearrangement causes a gain or loss of chromosome material.

65
Q

example of translocation that causes CML

A

BCR-ABL translocation, balanced translocation between 9 and 22

66
Q

impact of balanced translocation in BCR-ABL

A

makes philadelphia chromosome, where the fusion point of the chromosome makes a fusion protein made up of BCR with ABL tyrosine kinase, and is always active

67
Q

how does a Robertsonian translocation occur?

A

ONLY BETWEEN 2 ACROCENTRIC CHROMOSOMES

68
Q

mechanism of Robertsonian translocation?

A

short (p) arms of 2 non-homologous chromosomes are lost and the long arms fuse at the centromere to form a single chromosome

69
Q

effect on carrier of Robertsonian translocation

A

no effect, because short arms don’t contain essential genetic material

70
Q

karyotype of Robertsonian translocation carrier

A

45 chromosomes (bc 2 fused)

71
Q

what common condition could be caused by a Robertsonian translocation?

A

downs syndrome! 3 copies of 21 q arm, which mimics consequences of trisomy of the full chromosome 21

72
Q

example of chromosome translocation

A

Robertsonian translocation, downs syndrome

73
Q

example of chromosome deletions

A
  1. Cri-du-chat syndrome
  2. wolf-hirschhorn syndrome
  3. DiGeorge syndrome (22q11)
  4. williams syndrome
74
Q

characteristics of Cri-du-chat syndrome

A
  1. laryngeal defects that cause cat-like, high pitched cries.
  2. intellectual disability (IQ 35)
  3. microcephaly
  4. characteristic but not distinctive facial appearance
75
Q

deletion that causes Cri-du-chat?

A

deletion of distal end of short arm of chromosome 5 (contains genes important for development)

76
Q

deletion that causes Wolf-hirschhorn syndrome?

A

short arm 4p16 close to the centromere

77
Q

facial characteristics of Wolf-hirschhorn syndrome

A
  1. broad flat nasal bridge
  2. high forehead
  3. widely spaced eyes
  4. shortened distance between nose and lip
  5. downturned mouth
78
Q

characteristics of wolf-hirshhorn syndrome

A
  1. delayed growth and development
  2. failure to thrive
  3. hypotonia
  4. short stature
  5. skeletal and dental abnormalities
  6. cleft palate
  7. intellectual disability
  8. strong social skills with weak verbal skill
79
Q

what is most common microdeletion?

A

DiGeorge syndome! deletion in 22q11

80
Q

deletion in DiGeorge syndrome?

A

22q11

81
Q

effect of deletion of 22q11

A

defective embryonic migration of neural crest cells to developing structures of the neck, leading to functional defects of thymus, hypoparathyroidism and hypocalcemia

82
Q

characteristics of DiGeorge syndrome

A
  1. hypoparathyroidism
  2. hypocalcemia
  3. 80% heart defects
  4. cleft palate
  5. functional defects of the thymus
  6. developmental delay, ADD, anxiety, autism spectrum disorder
83
Q

2 of the microdeletion syndromes?

A
  1. Digeorge syndrome

2. williams syndrome

84
Q

deletion in Williams syndrome?

A

delted region contains elastin gene ELN and LIMK1

85
Q

what is the effect of the ELN deletion in Williams syndrome?

A

CV defects due to large amount of elastin in the blood vessels

86
Q

what is the effect of the LIMK1 deletion in Williams syndrome?

A

LIMK1 is kinase expressed in brain, so have visual spatial deficiencies

87
Q

characteristics of Williams syndrome

A
  1. CV defects
  2. poor visuospatial abilities
  3. mild intellectual disabilities
88
Q

facial features of williams syndrome

A
  1. broad forehead
  2. short palpebral fissure
  3. low nasal bridge
  4. full lips and cheeks
  5. relatively large mouth
89
Q

example of chromosome duplication

A

Charcot-Marie tooth disease

90
Q

how does chromosome duplication happen

A

uneven crossing over, making 2 copies of a specific region of DNA, less harmful than deletions and leads to partial trisomy

91
Q

what defect leads to partial trisomy?

A

chromosome duplication

92
Q

alternative name for charcot marie tooth

A

hereditary motor and sensory neuropathy (HMSN)

93
Q

what duplication causes CMT type 1A?

A

duplication on PMP22 gene on chromosome 17

94
Q

what results from duplication in PMP22 gene?

A

increased production of PMP22 protein, causing structure and function of myelin sheath to be abnormal

95
Q

what does PMP22 do?

A

integral membrane glycoprotein produced by Schwann Cells in the PNS

96
Q

what is the condition called with increased expression of PMP22?

A

demyelinating peripheral polyneuropathy

97
Q

characteristics of CMT?

A
  1. slow, progressive muscle weakness and atrophy
  2. upper extremity ataxia and tremor
  3. pes cavus (high arch)
98
Q

what is paracentric inversion?

A

inversion that does NOT include the region of the chromosome with the centromere

99
Q

what is pericentric inversion?

A

inversion that INCLUDES the centromere region of the chromosome

100
Q

what are chromosomal inversions considered?

A

balanced rearrangements, because they don’t lose any material

101
Q

what does inversions lead to?

A

difficulties with homologous recombination during meiosis

102
Q

diseases caused from chromosome inversions

A

HEMOPHILIA A

103
Q

explain hemophilia A

A

X linked recessive, mutations in gene for clotting factor VIII. hemarthroses, hemorrhages, bruising, intracranial hemorrhages

104
Q

what is a ring chromosome?

A

chromosome undergoes 2 breaks, which rearrange and fuses its own broken ends together to form a ring – super rare and unstable

105
Q

Ring chromosome 14 syndrome characteristics

A

seizures, intellectual disability, delayed cognitive and motor development, slow growth, short stature, microcephaly, lymphedema

106
Q

what is an isochromosome?

A

chromosome separates perpendicular to the axis of cell division, resulting in isochromosomes consisting soley of 2 copies of 1 arm (either p or q arms only)

107
Q

what does having an isochromosome lead to?

A

partial trisomy and partial monosomy

108
Q

what is the most common isochromosome?

A

long arm of chromosome X (turner syndrome)

109
Q

what is XP isochromosomes?

A

duplication of the long arm and no short arm (p), so it looks like a monosomy to the cell

110
Q

what does XP isochromosome lead to?

A

20% of the time, Turner syndrome

111
Q

what does 45XY, der(13;14) mean

A

a translocation has occurred (derivative)

MFM (39 decks)

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