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Medical Genetics > Karyotypic Abnormalities > Flashcards

Karyotypic Abnormalities Flashcards

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1
Q

How many cells does a karyotype typically analyze?

A

so it looks at living, dividing cells that are stopped in the middle of cell division

looks at chromo of 20 cells, deeply analyzing 5

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2
Q

What is the range for good band counts? poor band counts?

A

good = 550-650
poor = 350-450

(can dep on cell type, so like amniocytes will have weaker band count)

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3
Q

What ype of FISH can use cells that are not dividing?

A

Interphase FISH

(3-5 day turnaround time)

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4
Q

When is chromosomal disorder our first thought that comes to mind?

A

when you see a disorder that involved multiple unrelated systems + mult congenital anomalies

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5
Q

What is the suspected critical region os chr21?

A

21q21.22

but multiple regions are suspected; this is not quite known yet

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6
Q

What are 3 major anomalies in Tri21 taht we want to look for right away?

A
  • heart defect
  • duodenal atresia
  • Hirshsprung disease
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7
Q

What are some abnormal labs taht are associated with Tri21?

A
  • transient myelopoiesis (20-30% risk leukemia)
  • hypothyroidism
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8
Q

What are common cardiac findings in Tri21?

A

50% have heart anomalies:

40% AVSD
32% VSD
10% ASD
TOF 6%

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9
Q

Describe duodenal atresia and prevalence in Tri21

A

this is when the duodenum (C curve) has a blockage or discontinuity so that nothing can move through it –> baby cannot eat and stomach blows up w gas –> double bubble

25-40% kids w duo atresia have Tri21

5% kids w Tri21 have duo atresia

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10
Q

Describe Hirschsprung and its prevalence in Tri21

A

the ganglion cells (resp for squeezing + forward movement of stool) do not migrate to the rectum —> means absense of ganglion cells –> that area is small and v tight

leads to vomit + repeat –> baby needs surgical repair

this is V dangerous to send a child home w this

  • present in 2% Tri21
  • 12% w Hirsch have Tri21
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11
Q

What are some major physical findings in Tri21?

A

low tone (noticable right away)
microcephaly
brachycephaly
upslanting palpebral fissures
epicanthal folds
flat nasal bridge
tongue thrusting
small cupped ears
redundant nuchal skin
single palmar crease + clinodactyly 5th finger
sandal gap

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12
Q

What are some ENT + Vision problems we see in Tri21?

A

82% w frequent ear infections w conductive hearing loss (due to abnorm of eustachian tube bc absent nasal bone does not allow that pressure to equalize between the nose + the ear)

56% visual problems, usu near sighted

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13
Q

What are some autoimmune findings in Tri21?

A

risk of autoimmune disorders w thyroid + Celiac (bc have problems w absorption)

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14
Q

If patients w Tri21 are particularly active, what is something we want to look for?

A

they can have Atlanto-axial instability (base of skull to spine), so want to look at flexion and extension x-rays to make sure neck is ok

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15
Q

What is the avg age of development for Tri21?

A

2nd grader

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16
Q

Why is premature Alzheimer’s in adults common in Tri21?

A

the precursor protein in on Tri 21 (APP (amyloid precursor protein))

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17
Q

What are the fertility risks assoc w Tri21?

A

males = usu infertile
females = subfertile (15030% fertile)

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18
Q

What is risk for someone w Tri21 to have an affected child?

A

empirical data says 35-50%

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19
Q

What is approximate risk for woman age 40 to have child w Tri21?

A

1/100

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20
Q

What are the most common to least common causes for Tri21?

A

95% nondisjunction
- 90% maternal, 10% paternal
- 77% Mei I, 23% Mei II
- Mei I - usu maternal
- Mei II - usu paternal

4% Rob translocation
1% mosaicism
<1% partial dup

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21
Q

What are the recurrence risks of Tri21 w respect to the genetic cause?

A
  • Nondisjunction –> ~1-4% if <30y (then age related risk for >30y)
  • Rob trans –> empirically derived:
    — t(14:21) 10-15% maternal, <5% paternal
    —21q21a isochromosome: 100%
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22
Q

Causes of Tri18?

A
  • 94% maternal nondisjunction (usu Mei II) + association w mat age
  • 5% mosaicism
  • ~1% transloc or partial dup
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23
Q

What is the general prognosis for Tri18?

A

50% died w/in 1w birth

90% die by 1y (even w intervention) –> usu bc heart defect, primary apnea (stop breathing)

if they survive past 1y, then they are more likely to live longer

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24
Q

What are common physical findings in Tri18?

A

remember that everything is v small

  • char craniofacial features
  • overriding fingers
  • nail hypoplasia
  • short hallux
  • rocker bottom feet
  • short sternum
  • prominent occiput
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25
Q

What % of babies w Tri18 die in labor?

A

38%

also, 1/3 = premature

26
Q

What is the most common major congenital anomaly we see in Tri18?

A

90% heart defects (VSD, mult valve anomalies)

27
Q

What are major anomalies we see in Tri18 when thinking of Cardiac, Pulm, Opthalm, and ENT?

A
  • heart defects
  • respiratory problems (laryngomalacia, trachoebronchomalacia, apnea, pulm HTN)
  • opthalmology (10% cataract, corneal opacities, photophobia)
  • ENT (mod-severe sensorineural hearing loss bc v small ears)
28
Q

What are major anomalies we see in Tri18 when thinking of limbs, skeletal, renal, CNS?

A
  • Limb anom (5-10%, radial aplasia, club foot)
  • Skeletal (scoliosis - more when older)
  • Renal (2/3 w horseshoe kidney, UTI more common)
  • CNS (5% brain anom; 25-50% seizures)
    Also
  • inc risk for neoplasia: Wilms tumor (1% risk), hepatoblastoma
29
Q

What is the avg age for Tri18 developmentally?

A

older kids function at 6-8mo

30
Q

What are some speech + motor skills that are lacking in Tri18?

A

most have no expressive language

most cannot walk indep

CAN recognize fam + smile at them

older kids can maybe understand words, crawl, follow command, interact a bit w others

31
Q

Can parents always opt for surgical intervention for Tri18?

A
  • dep on institution
  • some will not provide surg intervention, some will for VSD for ex
  • want to respect parents wishes + also being realistic
32
Q

Why do those w Tri18 need an abdominal US every 6 months?

A
  • want to check for renal malformation + Wilms tumor + hepatoblastoma
33
Q

3rd most common trisomy?

A

Tri13 (Patau syndrome)

34
Q

What are 2 big features that you want to think about when thinking of Tri13?

A

holoprosencephaly
cutis aplasia (think of that region on scalp that has no skin closure)

35
Q

What are other main physical features of Tri13 other than holoprosencephaly + cutis aplasia?

A
  • polydactyly
  • renal anomalies
  • eye anomalies (anophthalmia, microphthalmia)
36
Q

What are som congenital anom assoc w Tri13?

A

CNS: holoprosencephaly, Dandy Walker (cerebellum)

Heart: VSD, ASD, TOF, transposition of the great arteries

GU: polycystic kidneys, uterine agenesis

37
Q

What is the prognosis for Tri13?

A
  • 50% die w/in 1month
  • 90% die w/in 1year (recent studies say maybe survival of 20%)
38
Q

What are genetic causes of Tri13?

A

91% nondisjunction, usu Mei I

39
Q

What are 3 prenatal indications for Turner syndrome?

A

hydrops, cystic hygroma, heart defect

40
Q

What are some findings that might present in childhood/puberty to make the dx of Turner syndrome?

A

childhood
- isolated short stature
puberty
- primary amenorrhea
- lack of secondary sex char

also, hypothyroidism

41
Q

What are some birth anomalies associated with Turner syndrome?

A
  • webbed neck
  • downslanting eyes
  • low set ears, posteriorly rotated
  • wide chest (w widely spacednipples)
  • puffy hands and feet (edema)
  • hyperconvex nails
42
Q

What explains the short stature in Turner syndrome?

A

SHOX deficiency
- can also see Madelung deformity (radius shortened w curvature of the arm)

of note, can be responsive to growth hormone bc can overcome the signaling pathway

43
Q

What explains the amenorrhea in Turner syndrome?

A

streak gonads –> since they are resp for providing estrogen for secondary sex devel

subfertility to infertility = typical
POF

44
Q

Why might we see weight gain in Turner syndrome?

A

if they have hypothyroidism, then there may be poor metabolism in the muscles

45
Q

What are common endocrine disorders associated with Turner syndrome?

A

95-100% w growth failure + red adult ht

90-95% w hypergonadotropic hypogonadism (gonads not resp well to the gonadotropins (FHS, LH) –> then they tell ovaries to release hormones, which cannot happen in this case)

15-50% glucose intolerance

Type I diabetes
10% Type II diabetes

46
Q

What are some main features of Klinefelter syndrome (47,XXY)?

A

hypergonadotropic hypogonadism (pituitary is great, then testes do not respond)

male factor infertility

tall stature

low tone

difficulties in school (w ELA)

trouble regulating emotions

47
Q

Why do those w Klinefelter syndrome (47,XXY) have tall stature?

A

they have an extra copy of SHOX

48
Q

How are Klinefelter and Triple X simialr in presentation?

A
  • speech dev delays
  • motor dev delays
  • mild reduction in IQ, usu more so bc of immaturity
  • tall stature
  • low tone
49
Q

What trisomy had been historically ties to inc risk of imprisonment?

A

XYY Jacob’s syndrome

those were biased though, we know now that they usu have inc risk of autism, ADHD, emotional control

50
Q

What causes Wolf-Hirschhorn?

A

4p-

55% w terminal del
Ring 4 chromo
4p- mosaicism
unbalanced transloc

51
Q

What was a historical way to describe Wolf-Hirschhorn?

A

Greek warrior helmet facies

52
Q

What are the most common findings in Wolf-Hirschhorn? (>75%)

A
  • IUGR/postnatal growth def
  • ID
  • hypotonia
  • muscle hypertrophy (become small and skinny)
  • seizures
  • feeding difficulties
  • abnormal ears
53
Q

What are the less common findings in Wolf-Hirschhorn? (<75%)

A

50-75%:
- EEG abnorm
- skeletal anom
- craniofacial asymm
- abnormal teething
- ptosis
- antibody def

25-50%:
- heart defects
- hearing defects
- eye/optic nerve defects (like coloboma)
- cleft/lip palate
- structural brain anom
- GU tract defects
- renal anom

54
Q

What causes cri du chat?

A

5p-

80-90% paternal in origin
10-15% due to unbal parental transloc
80-90% term del
3-5% bc interstitial del

uncommon=mosaicism, inversions, ring chromo

55
Q

What are the main findings associated with cri du chat?

A

laryngeal malformation resulting in high pitched monotone cry (hear meowing sound in nursery)

dev delay/ID

craniofacial findings

other congen anom

56
Q

What are some facial features associated with cri du chat?

A
  • round face
  • prominent metopic bossing
  • broad nasal bridge, lateral downslanting palpebral fissures
  • hypertelorism
  • epicanthal folds
  • strabismus divergent/convergent
  • short philtrum
  • down turned corners of mouth
  • low-set ears

of note, high arched palate is a big one

dysm feat are not a dead giveaway for this one

57
Q

What are some medical features associated with cri du chat?

A

35% congenital heart disease

30% abnormal MRI
- absense corpus callosum
- small cerebellum

18% renal abnorm
- small kidneys, ectopic

gential abnorm
- cryptorchidism
- inguinal hernia

dev delay
- mod to sev (dep on the del)

58
Q

What is the cause of cat-eye syndrome?

A

isodicentric marker 22q11 –> tetrasomy

q region gets dup around centromere

59
Q

What are main findings in cat-eye syndrome?

A
  • coloboma = “cat eye” (due to the defect in dev of the optic nerve)
  • preauricular anom (pits, tags)
  • hearing loss
  • heart defect
  • renal anom
  • anal atresia
  • ID (mild)
60
Q

What are the causes of Turner syndrome?

A

40-50% = 45,X
15-25% = mosaicism 45,X/46,XX
20% = isochromosome

ring X = present in a few women
10-12% women have some Y material
(~3% present 45,X/46,XY)

Medical Genetics (14 decks)

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