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CSF block 6 > clinical cytogenetics > Flashcards

clinical cytogenetics Flashcards

1
Q

what are the subtelomeric regions?

A

gene rich areas just proximal to the telomere

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2
Q

define metacentric/sub-metacentric/acrocentric

A

metacentric- centromere in the middle
sub-metacentric- centromere closer to one end
acrocentric- centromere at the end

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3
Q

when is the best time in the “cell cycle” to view and analyze chromosomes?

A

better when chromosomes are longer and less condensed (like mitotic cells)

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4
Q

what are some prenatal reasons to perform cytogenetics? (4)

A

risk for aneuploidy
abnormal US
FHx of chromosomal anomaly
advanced maternal age

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5
Q

what are some reasons to perform postal natal cytogenetics? (6)

A 
multiple congenital anomalies 
MR/growth delay
ambiguous genitalia
infertility/SAbs
leukemia/solid tumor 
FHx of chromosomal anomaly
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6
Q

what are two tissue types that are appropriate for chromosome analysis?

A

lymphocytes and fibroblasts

need dividing cells

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7
Q

from where are lymphocytes derived?

A

peripheral blood, cord blood, bone marrow

place in sodium heparin preservative

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8
Q

from where are fibroblasts derived?

A

solid tissue bx, amniotic fluid, chorionic villi

place in sterile saline media

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9
Q

what are the steps in chromosome analysis? (7)

A
  • obtain sample
  • grow cells in media (time varies)
  • harvest cells
  • make/band slides
  • scan slides to look for cells in metaphase
  • analyze/capture/karyotype cells
  • review/sign out results
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10
Q

what is a normal female? normal male?

A

female 46, XX

male 46, XY

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11
Q

what is aneuploidy?

A

having a chromosome number that is not equal to a multiple of haploid number (n = 23)

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12
Q

how is trisomy 21 denoted? monosomy 22?

A

47, XX, +21 (most common aneuploidy)

45, XY, -22

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13
Q

what are the 2 mechanisms of triploidy?

A

dispermy, disomic egg

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14
Q

describe dispermy

A

normal egg fertilized by 2 sperm
most lost at 10-20 weeks after conception
abnormal placenta with growth-retarded fetus

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15
Q

describe disomic egg

A

disomic egg had error in meiosis II or retention of polar body
severely growth retarded fetus, small placenta, large head
some survive to birth

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16
Q

what is mosaicism?

A

presence of 2 or more cell lines in an individual or tissue sample

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17
Q

what yield a larger abnormality with mosaicism?

A

error that occurs earlier in fetal life

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18
Q

when do oogonia begin to develop in fetal life?

A

12th week

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19
Q

when does oogonia development arrest?

A

arrests in prophase I around 20 weeks (dichtyotene stage)

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20
Q

why is it proposed that more non-disjunction events occur in females with advanced maternal age?

A

because of oogenesis as an embryo vs. males who continually produce sperm throughout life

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21
Q

what is nondisjunction?

A

improper separation of chromosomes during meiosis, can happen in meiosis I or II

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22
Q

what happens when nondisjunction occurs in meiosis I?

A

homologs do not separate

23
Q

what happens when nondisjunction occurs in meiosis I?

A

sister chromatids fail to separate

24
Q

what is the m/c cause of trisomy 21?

A

maternal meiosis I erros

25
Q

what are all the possible causes of trisomy 21?

A

maternal meiosis errors (I/II)- 85-90%
paternal meiosis erros (I/II)- 3-5%
mitotic errors (mosaicism)- 3-5%
robertsonian translocation/other - 5%

26
Q

does the presence on mosaic T21 help to predict severity?

A

No

27
Q

where is the translocation tha causes T21?

A

robertsonian translocation of chromosome 21 to chromosome 14, unbalanced
46, XY, der(14;21)(q10;q10),+21

28
Q

what is T18?

A

Edward’s syndrome

fist clenching, rocker bottom feet, prominent occiput, low set ears

29
Q

was is T13?

A

Patau syndrome

midline defects, clefting, polydactyly

30
Q

what is turner syndrome?

A

45,X

can be mosaic with 46,XX or 46,XY cells

31
Q

what is Kleinfelter Syndrome?

A 
47, XXY males
delayed puberty
mall stature, long legs
gynceomastia
decreased IQ
32
Q

what is 47,XXX?

A

females

reduced IQ, learning disabilities, increased vulnerability to stress

33
Q

what is 47,XYY?

A

males
tall stature
?behavioral problems, decreased IQ

34
Q

what is the SYR?

A

sex-determining region ont he Y chromosome
conserved sequences is DNA binding domain that is believed to be a transcription factor
found in all mammals

35
Q

what is the germinal ridge?

A

testes determining factor

36
Q

which chromosomes can be involved with robertsonian translocations?

A

acrocentric chromosomes

13, 14, 15, 21, 22

37
Q

what defines “robertsonian translocation”?

A

involves the fusion of 2 long arms and loss of the short arms, if the short arms contain only repetitive DNA, can have a balances translocation and normal phenotype

38
Q

what can robertsonian translocations increase the risk of?

A

infertility or trisomic conception (esp females)

39
Q

contrast balanced vs. unbalanced translocations

A

balanced- no material lost/gained, just rearranged- normal phenotype
unbalanced- abnormal phenotype

40
Q

what is the risk of mental or physical abnormalities in people with inherited translocations vs de novo?

A

inherited ~2%
de novo 10-15%
can lead to increased pregnancy loss/infertility

41
Q

define terminal vs interstitial deletion

A

loss of material
terminal- one break, at the end
interstitial- 2 breaks

42
Q

define paracentric vs. pericentric inversions

A

paracentric- avoid the centromere (same arm)

pericentric- include the centromere (both arms)

43
Q

what is FISH?

A

florescence in situ hybridization
detects chromosomal abnormalities in interphase cells
various probes

44
Q

what are the uses of different FISH probes?

A

microdeletion syndromes- unique probes
centromere- repetitive probes
libraries- painting probes

45
Q

what are the pros of FISH? (3)

A
  • used in non-dividing cells (like SAb)
  • detect subtle rearrangements
  • quick turnaround
46
Q

what are the cons of FISH? (3)

A
  • must know target
  • may not reliably detect tandem duplications
  • may not detect mosaicism reliably
47
Q

what are the 2 types of microarray analysis?

A

Comparative genetic hybridization (CGH)

Single nucleotide polymorphism (SNP)

48
Q

what is the basis of CGH?

A

patient and control DNA are labelled with different colors and analyzed for gains/losses

49
Q

what are the minimum sizes of gains/losses that can be detected by CGH?

A

gains- 500 kb

losses- 200 kb

50
Q

what is the basis of SNP?

A

patient DNA is hybridized to a slide with DNA probes that are differentially labelled according to whether they are AA, AB, BB at many SNPs across the genome; computer calculates if there is gain/loss/loss of heterozygosity

51
Q

how is SNP analysis interpreted?

A

deletion- decreased intensity
gain- increased intensity
ROH- neutral intensity

52
Q

what are the pros of chromosome analysis? (4)

A
  • view of entire genome
  • detect balanced rearrangements
  • detect polyploidy
  • provide insight to etiology
53
Q

what are the cons of chromosome analysis? (3)

A
  • must have actively dividing cells
  • lower resolution of detection
  • longer turnaround time

CSF block 6 (5 decks)

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