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Clinical Genetics > Cytogenetics > Flashcards

Cytogenetics Flashcards

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1
Q

There are 10 indications for a blood karyotype. Name as many as you can

A 
primary amenorrhea
infertility
recurrent pregnancy loss/stillbirth
ambiguous genitalia
small testes, delayed puberty in males
short stature
dysmorphic features, growth impaired
mental retardation
family history of chromo. rearrangement
hematological malignancy
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2
Q

when would you do a skin biopsy?

A

chromosomal mosaicism suspected

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3
Q

give 5 steps of a karyotype

A
  1. culture tissues/cells
  2. stimulation cell division with PHA
  3. mitotic block with colcemid
  4. treat w/ trypsin to release proteins
  5. stain with Giemsa
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4
Q

what changes does a karyotype detect?

A

> 5 Mb changes

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5
Q

what chromo changes can be balanced rearrangment (4)

A

inversions
insertions
translocations
robertsonian translocation

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6
Q

what is the recurrence issue w/ balanced?

A

offspring of carrier at risk to unbalanced

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7
Q

phenotypic consequences of translocation?

A

rarely any at all bc between non homologous

offspring at risk of being unbalanced

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8
Q

pericentric vs. paracentric

A

peri - includes centromere. can have unbalanced children

para - doesn’t include centromere. only balanced offspring

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9
Q

what chromo changes can happen in unbalanced rearrangements

A

deletions
duplications
isochromosomes
unbalanced translocations

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10
Q

deletions and duplications can occur by what mechanisms? (4)

A

abnormal segregation from inversion, insertion
translocation

NAHR

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11
Q

what happens in confined placental mosaicism?

A

nondisjunction post-zygotically
zygote is trisomic
trisomy rescue - one chromosome is removed giving disomy

placental tissue from CVS is abnormal, but fetus turns out to be normal

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12
Q

what are the relevant aneuploidys?

A

trisomy 13, 18, 21, Klinefelter (XXY), Turner (monosomy X)

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13
Q

what are the three causes of Downs

A

freestanding trisomy 21
RT (spontaneous)
RT (parental carrier)

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14
Q

List some of the clinical features of Downs in neonates

A

congenital HD
hypotonia
duodenal atresia
hematologic issues

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15
Q

list some of the childhood clinical features of Downs

A 
developmental delay
mental R
strabismus
alantoaxial instability
slow growth
hearing loss
hypothyroidism
leukemia
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16
Q

list some of the adult issues in downs

A

premature aging
alzheimers
shortened life expectancy

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17
Q

what is down recurrence risk?

A

1-4% for any nondisjunction

downs responsible for half that

18
Q

clinical features of trisomy 18?

A 
clenched hands
congenital HD
small for gestational age
abnormal facial features
feeding problems
failure to thrive
19
Q

prognosis for trisomy 18?

A

30% survive one month
10% one year
Death secondary to apnea, aspiration, seizures
Survivors profoundly MR

20
Q

clinical features of trisomy 13?

A 
polydactyl
microcephaly
holoprosencephaly
scalp defects
hypotelorism, micropthalmia, midline facial clef
21
Q

prognosis for trisomy 13?

A

40-50% survive one month
10% one year
Death secondary to apnea, aspiration, seizures
Survivors profoundly MR

22
Q

turner syndrome genetics?

A

45,X (50%)
mosaic (40%) (45,X/46XY or XX)
others from strxal X aberrations, translocations, isochromosome Xq

23
Q

clinical features of newborn with turner syndrome?

A 
nuchal skin redundancy
low posterior hairline
upturned earlobes 
puffy hands and feet
inverted nails
broad chest
24
Q

birth defects in turner syndrome?

A 
congenital heart disease
kidney strxal abnormalities
lympedema
cystic hygroma
nuchal redundancy
25
Q

natural history of turner syndrome?

A 
small stature (secondary to SHOX hemizygosity)
ovarian failure --> primary amenorrhea, infertility
no mental R but some mild disability in visuo-spatial
26
Q

genetics of klinefelter syndroms?

A

47,XXY or more X chromosomes (less severe)
meiotic nondisjunction
maternal > paternal
weak maternal age effect

27
Q

clinical features of klinefelter

A

normal in childhood then get tall stature
most develop normal cognitively
some get malignancy, CV issues, immunogenic

28
Q

why are microdeletions and microduplications important in clinical genetics?

A

important cause of cognitive disability, congenital anomalies, genetic variation

29
Q

what are some uses of FISH

A

delineate translocations
identify marker chromosomes
detect deletions or duplications
can use in dead/nondividing cells

30
Q

what are some uses/nonuses for array CGH

A

can’t see low level mosaicism or balanced rearrangements

autism or pt with unexplained MR
CNV analysis

31
Q

what is the williams syndrome deletion?

A

7q11.23

32
Q

what is the williams syndrome phenotype?

A 
overlyfriendly behavior
unusual facial features
growth impairment
congenital HD (SVAS, elastin arteriopathy)
urinary tract abnormalities
endocrine issues
33
Q

genotype-phenotype correlation?

A

ELN deletion - elastin. SVAS

LIMK1 deletion - lim kinase. visuospatial cognition

34
Q

what is the deletion in DiGeorge syndrome?

A

22q11

35
Q

what is the DiGeorge phenotype?

A 
congenital HD
cleft palate
hypocalcemia from hypoparathyroidism
immune deficincy
developmental delay
behavioral issues
36
Q

how common is DiGeorge?

A

most common microdeletion

37
Q

What is the Cri du Chat phenotype?

A

high pitched cry
microcephaly
MR
characteristic facial features

38
Q

Cri du Chat phenotype?

A

terminal deletion on chromosome 5p

39
Q

Cri du Chat genotype-phenotype

A

fine positional mapping allows for delineation of what deletions lead to what phenotype

40
Q

what is worse – a large or small pericentric inversion and why

A

Large inversions are less severe
Crossing over gives less loss of chromosomal material

Small inversions are more severe
Crossing over gives more loss of chromosomal material

Clinical Genetics (6 decks)

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