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Molecular Foundations of Medicine > Chromosomal Disorders > Flashcards

Chromosomal Disorders Flashcards

1
Q

aneuploidy

A

any chromosome number that is not an exact multiple of the haploid number (23)

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2
Q

leading genetic cause of intellectual disability

A
  • aneuploidy

* common forms: trisomy and monosomy

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3
Q

trisomy statistics

A
  • autosomal trisomies make up about 30% of aneuploidy

* trisomy 16 is the most common (~15%), but never seen in liveborns

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4
Q

monsomy x statistics

A
  • make up about 10% of aneuploidy

* 99% abort

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5
Q

monsomies of autosomes

A

complete monosomies = lethal

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6
Q

most common parental origin of 45,X

A

mainly paternal NDJ

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7
Q

parental contributions to XXY

A

maternal and paternal NDJ roughly equal

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8
Q

parental origins of trisomies 21, 18, 13 and XXX

A

primarily maternal, and primarily MI NDJ

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9
Q

dysmorphology of down syndrome (trisomy 21)

A
  • upslanting palpebral fissure
  • overfolded helices
  • single palmar transverse crease
  • short, bent 5th fingers
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10
Q

other problems associated with down syndrome

A
  • congenital heart disease (40-50%)
  • hearing loss due to otisis media
  • strabismus and refractive errors
  • hypothyroidism
  • moderate intellectual disability
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11
Q

statistics of causes of down syndrome

A
  • 95% due to NDJ
    • 75% meiosis I
    • 25% meiosis II
  • 4% robertsonian translocation 21;14 or 21;22
  • ~1% mosaic trisomy 21
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12
Q

Presentation of Trisomy 18 (edwards syndrome)

A
  • low frontal hairline
  • short palpebral fissures
  • bluntanasal tip with small nostrils
  • small chin
  • “fawn-like” ears
  • high nasal bridge
  • short sternum
  • overlapping fingers w/ clenched fists
  • genital anomaly
  • possible missing digits
  • rockerbottom feet
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13
Q

other problems associated with trisomy 18

A
  • cardiac defect
  • renal anomaly
  • severe intellectual disability
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14
Q

Presentation of Trisomy 13 (patau syndrome)

A
  • holoprosencephaly with premaxillary agenesis (atypical median cleft lip/palate)
  • micropthalmia
  • short, prominent sternum
  • flexed fingers
  • polydactyly
  • “rocker-bottom feet”
  • abnormal scrotum/micropenis
  • normal birthweight
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15
Q

other problems associated with trisomy 13

A
  • cryptorchidism
  • cardiac defects (VSD common)
  • cystic dysplastic kidneys
  • omphalocele
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16
Q

5p- syndrome presentation

A
  • aka cri du chat syndrome
  • cat like cry due to hypotonia and laryngeal abnormality
  • growth restriction
  • microcephaly
  • round face, widely spaced eyes
  • single palmar crease
  • moderate to severe intellectual disability
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17
Q

microdeletion syndromes

A
  • sometimes called contiguous gene deletion syndromes

* may not be detected on karyotype; FISH and microarray allow more detail

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18
Q

22q11.2 deletion syndrome presentation

A
  • previously DiGeorge or Velocardiofacial syndrome
  • Autosomal dominant!
  • mild facial dysmorphology
  • cleft palate
  • slow growth
  • others associated with 4th pharyngeal arch, and 3rd/4th pouches
19
Q

other problems associated with 22q11.2 deletion syndrom

A
  • thymus and parathyroid
  • cardiac defects (interrupted aortic arch, tetralogy of fallot)
  • also VSD
20
Q

Mechanisms of 22q11.2 deletion

A
  • non-allelic homologous recombination (NAHR)

* LCRs thought to be involved in crossover and may be implicated with the deletion

21
Q

a good test for 22q11.2 deletion syndrome

A

FISH

Autosomal dominant

22
Q

WAGR syndrome

A
  • microdeletion on 11p13
  • W=wilms tumor of kidney -> WT1 gene at 11p13
  • A=Aniridia (no iris) -> del of PAX6 gene at 11p13
  • G=genital anomalies -> del of WT1 at 11p13
  • R=retardation of growth and dev
23
Q

Williams syndrome presentation

A
  • a contiguous gene deletion; microdeletion of 7q (elastin gene)
  • depressed nasal bridge
  • blue eyes, stellate pattern
  • long philtrum, wide mouth
  • delayed development, cocktail personality
24
Q

Klinefelter syndrome presentation

A
  • 47, XXY (one or more extra X)
  • small firm testes
  • hyalinization of seminiferous tubules with azospermia
  • long limbs
  • gynecomastia: breast cancer risk = with that of women
  • variant: 48, XXXY mental retardation and dysmorphology
  • may need testosterone therapy
25
Q

key points of XXX, XXY, and XYY

A
  • ~10 IQ deficit compared with family
  • most employed and married
  • reported over-representation in psych hospitals
  • generally good outcome if low stress home
26
Q

47, XYY and 47, XXX

A
  • not syndromes -> no abnormal phenotype, generally normal fertility
  • offspring usually chromosomally normal
27
Q

turner syndrome

A
  • absence of a normal second sex chromosome in females
  • phenotypically female
  • absence of all or part of an X chromosome
  • 50% 45, X
  • 25% mosaic (may include Y)
  • various X deletions, rings, isochromosomes
28
Q

diagnosis of turner syndrome

A
  • newborns: edema of hands and feet, web neck
  • adolescents: lack of puberty and short stature
  • suspect in any girl with short stature
  • can have coarctation of aorta
  • 80% due to absence of father’s X or Y
29
Q

46, XY female

A
  • SRY gene on Y chromosome has been deleted -> no development of male sex organs
  • 2nd X is needed in females for ovarian maintenance -> streak gonads in 46, XY female
30
Q

What is deletion of WT1 gene at 11p13 associated with

A

wilms tumor of kidney
AND genital anomalies
WAGR syndrome

31
Q

what is deletion of PAX6 gene at 11p13 associated with

A

aniridia (no iris)

WAGR syndrome

32
Q

Other problems associated with Williams syndrome

A
  • supravalvular aortic stenosis (75%) (ELN gene may be involved)
  • hyperalcemia (33%)
33
Q

deletion involved in williams syndrome

A

7q (elastin or ELN gene)

34
Q

Key presentation of turner syndrome in newborns

A

edema of hands and feet, web neck

35
Q

key presentation of turner syndrome in adolescents

A

lack of puberty and short stature

36
Q

other problems associated with turner syndrome

A

can have coarctation of aorta

37
Q

what should be suspected in any female with short stature?

A

turner syndrome

38
Q

most of turner syndrome is caused by

A

80% due to absence of father’s X or Y

39
Q

common presentations of turner syndrome

uworld

A
  • narrow, high-arched palate
  • low posterior hairline
  • broad chest, widely spaced nipples (shield chest)
  • cubitus valbus (forearm angled away from body to a greater degree than normal)
  • short stature
40
Q

common associated problems with turner syndrome

uworld

A
  • coarctation of aorta
  • bicuspid aortic valve (most common cardiac abnormality in TS)
  • horseshoe kidney
  • streak ovaries, amenorrhea, infertility
41
Q

Abnormalities of lymphatic outflow in turner syndrome can cause:

A
  • cystic hygroma (posterior neck mass)

* lympedema (can be described as bilateral extremity swelling)

42
Q

diminished femoral pulses could be suggestive of

A

coarctation of the aorta

43
Q

most common gastrointestinal complication in down syndrome babies

A

duodenal atresia

Molecular Foundations of Medicine (21 decks)

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