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MedGen > Common Aneuploidies, Microdeletions, and Duplication Syndromes > Flashcards

Common Aneuploidies, Microdeletions, and Duplication Syndromes Flashcards

1
Q

Which aneuploidies have a 100% rate of spontaneous abortions?

A

Trisomy 16
Triploid or Tetraploid
Other trisomies that are not T13,18, or 21 have a 99.5% rate

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2
Q

Phenotypic features of trisomy 21

A

FACE: epicanthal folds, upslanting palpebral fissues, Brushfield spots, flat nasal bridge, small mouth, small ears, protruding tongue
HEAD/NECK: flat facial profile, flat occiput, excessive skin on nap of neck, short neck
EXTREMITIES: single transverse palmar crease, clinodactyly, short broad hands, sandal gap toes
short stature
hypotonia

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3
Q

Trisomy 21:

  • Incidence
  • Life expectancy
  • chromosomes
A

INCIDENCE: 1/850
- 20-25% of T21 conceptuses survive to birth
- risk increases with maternal age
LIFE EXPECTANCY: 55 yrs old
- most common cause of early mortality is congenital heart disease
CHROMOSOMES
- 95% have T21 (recurrence risk is 1%)
- 4% have Robertsonian translocation (recurrence risk is 10%)
- ~2% are mosaic –> maybe milder phenotype

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4
Q

Trisomy 18:

  • Incidence
  • Life expectancy
  • Chromosomes
A 
INCIDENCE: 1:6,000-8,000 (live births)
- risk increases with maternal age
- 3:1 female-to-male ratio
LIFE EXPECTANCY:
- 50% die within the first 2 weeks of life
- 5-10% survive the first year of life
- Major causes of death: central apnea, cardiac failure (due to malformations), respiratory insufficiency (due to hypoventilation, aspiration, or upper airway obstruction
CHROMOSOMES:
-T18
- translocation including chr 18
- mosaicism
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5
Q

Phenotypic feature of Trisomy 18

A 
FACE: micrognathia, pointy low set ears
HEAD/NECK: prominent occiput
EXTREMITIES: clenched fist with overlapping fingers
CARDIOVASCULAR: (affects 50%); VSD, PDA
GASTRIONTESTINAL: (affects 75%); Meckel diverticulum, malrotation
OTHER:
- short sternum
- hypertonia
- IUGR
- Feeding difficulties
- severe intellectual disability
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6
Q

Trisomy 13:

  • incidence
  • life expectaqncy
  • chromosomes
A 
INCIDENCE: 1:12,000-20,000
LIFE EXPECTANCY: 
- 50% die within first month
- >90% die within first year
CHROMOSOMES:
- T13
- Unbalanced Robertsonian Translocation
- Mosaicism
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7
Q

Phenotypic features of Trisomy 13

A

FACE: sloping forehead, cleft lip/palate, micro/anophthalmia, colobomata
HEAD/NECK: microcephaly
EXTREMITIES: postaxial polydactyly, rocker-bottom feet
CARDIOVASCULAR: (affects 80%); VSD, ASD, PDA, dextrocardia
CNS: holoprosencephaly
OTHER:
- severe intellectual disability

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8
Q

Sex chromosome aneuploidies

  • incidence
  • indications for testing
  • why is phenotypic expression of sex chromosome abnormalities generally less severe than those of autosomal disorders?
A

incidence: 1/400 live births
- most common are trisomies, less frequent are monosomies

indications for testing:
- delay in onset of puberty, primary or secondary amenorrhea, infertility, ambiguous genitalia

phenotypic expression of sex chromosome abnormalities is generally less severe than those associated with autosomal disorders because of:

  • X-chromosome inactivation
  • low gene content on Y chromosome
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9
Q

Klinefelter Syndrome

  • incidence
  • chromosomes
  • causes
A

INCIDENCE: 1:600 live male births

  • underdiagnosed: only 25-50% diagnosed
  • mean age of diagnosis: 30 years old

CHROMOSOMES:

  • 47,XXY (1:600)
  • 48, XXXY (1:25,000)
  • 15% are mosaic

CAUSES:
- half of cases result from nondisjunction in paternal meiosis I, other half from nondisjunction in maternal meiosis I

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10
Q

Symptoms of Klinefelter syndrome

  • physical
  • cognitive
  • fertility
A

PHYSICAL:

  • gynecomastia
  • narrow shoulder
  • long legs
  • small testes
  • Underdeveloped secondary sexual characteristics

COGNITION:

  • low-normal verbal IQ
  • learning difficulties
  • behavior: poor social adjustments

FERTILITY:

  • infertility due to progressive destruction of seminiferous tubules and Leydig cells –> decreased sperm and testosterone production
  • hypogonadism
  • azoospermia in 10%
  • puberty at normal age
  • androgen deficiency –> loss of libido, decreased bone deficiency
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11
Q

47, XYY

  • incidence
  • management
A

INCIDENCE: 1:1000 live male births
- underdiagnosed

MANAGEMENT: neurodevelopmental evaluation and special education

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12
Q

Trisomy X

  • incidence
  • phenotype
  • cognition and behavior
  • fertility
  • management
A

INCIDENCE: 1:1000 live female births
- most common sex chromosome abnormality in females
- usually diagnosed incidentally on prenatal screening, but most never diagnosed
PHENOTYPE: taller than average, hypotonia
COGNITION:
- delayed milestones
- language and learning difficulties
- verbal and performance IQ decreased
BEHAVIOR: may have reduced social skills
FERTILITY: may have premature ovarian failure
- not at increased risk of having chromosomally abnormal offspring
MANAGEMENT: monitor for developmental delays

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13
Q

Turner Syndrome

  • Incidence
  • Chromosomes
  • Management
A

INCIDENCE: 1:2500-4000 live female births
CHROMOSOMES:
- 45, X –> 45% of cases; usually derived from mother
- mosaic (45,X/46,XX) –> 50% of cases
- X-chrom abnormalities –> ring chrom or isochromosome or p/q deletion

MANAGEMENT: monitor for developmental delays

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14
Q

Symptoms of Turner Syndrome

- phenotype

A

PHENOTYPE:

  • short stature
  • webbed neck
  • low set, posteriorly rotated ears
  • low posterior hairline
  • Broad chest and wide spaced nipples
  • lymphedema in newborns
  • Cubitus valgus
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15
Q

Features of Turner syndrome

  • cardiac
  • renal
A 
Recurrent otis media in 50-70% of patients
Increased risk of autoimmune disorders
CARDIAC
- up to 50% of patients
- coarctation of aorta
- bicuspid aortic valve
RENAL
- 20-30% of patients
- horseshoe kidney
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16
Q

Turner syndrome management

A

Cardiovascular evaluation

  • MRI to monitor for aortic dilation at least every 5 years
  • aggressive BP control

Growth hormome therapy

estrogen replacement therapy, starting at puberty

17
Q

What is the mechanism for deletion or duplication products in Microdeletion and Duplication syndromes?

A

unequal crossing over between misaligned sistids or homologous chromosomes containing highly homologous copies of segmentally duplicated sequences

  • -> results either in haploinsufficiency or overexpression of 1+ genes
  • occurs mostly in pericentromeric and subtelomeric regions
18
Q

22q11. 2 deletion syndrome
- what is it?
- cause
- incidence

A 
WHAT IS DIGEORGE SYNDROME?
defective development of the pharyngeal pouch syndrome
- thymus, thyroid, parathyroids
- maxilla, mandible
- Aortic arch, cardiac outflow tract
- external/middle ear

CAUSED BY: heterozygous del of 3 Mb (includes TBX1)

INCIDENCE: 1:4000 births

  • most prevalant microdeletion syndrome
  • underdiagnosed (phenotype can be mild)
  • 90% of cases are de Novo
19
Q

22q11. 2 syndrome features
- phenotype
- cardiovascular
- “other”

A

PHENOTYPE:

  • low set, posteriorly rotated ears
  • hypertelorism
  • bulbous nasal lip
  • palate abnormalities

CARDIO:
-80% of patients have congenital heart disease, including interrupted aortic arch, truncus arteriosus, ToF, ASD, VSD

OTHER:

  • developmental delay
  • T-cell deficits
20
Q

Williams syndrome

  • incidence
  • cause
A

incidence: 1:7500
cause: heterozygous del of 1.5 to 1.8 Mb at 7q11.23 (includes elastin gene)

21
Q

Williams syndrome features

A 
PHENOTYPE:
- broad forehead, periorbital fullness, hypertelorism, stellate pattern of iris, long philtrum, thick vermillon border of lips, wide mouth, small jaw
Mild to moderate intellectual disability
Renal artery stenosis
constipation
failure to thrive
SN or conductive hearing loss
22
Q

Prader Willi syndrome

  • causes
  • incidence
A 
most common cause of obesity
CAUSES
- 15q11.2-q13 del: 70% (pat)
- uniparental disomy: 20-30% (mat)
-Imprinting center mutation - 2.5%
- gene mutations - rare
- unknown: <1%

INCIDENCE: 1:10,000

23
Q

PWS phenotype

A 
FACE: narrow, bifrontal diameter, almond-shaped eyes, narrow nasal bridge, thin upper lip, small hands and feet
neonatal hypotonia, poor suck
Hyperphagia
Obesity  and concern of diabetes
small hands and feet
Short stature
hypogonadism
ID
24
Q

Angelman syndrome

  • causes
  • incidence
A

CAUSES:

  • 15q11.2-q13 del: 70% (mat)
  • uniparental disomy: 7% (pat)
  • Imprinting center mutation - 3%
  • gene mutations - 10% (UBE3A mut)
  • unknown: 10%

INCIDENCE: 1:12,000

25
Q

Angelman Syndrome features

  • phenotype
  • neurodevelopment
  • behavior
A

FACE: large jaw and widely spaced teeth, strabismus
HEAD: PROGRESSIVE microcephaly

NEURO: jerky movements, gait ataxia, absence of speech, seizures
Scoliosis
short stature
severe ID
drooling

*unique clinical features usually manifest after 1 yr

BEHAVIOR:

  • very happy
  • inappropriate laughter
  • excitable
  • sleep disturbances
26
Q

XYY features

  • phenotype
  • cognition
  • behavior
  • fertility
A 
PHENOTYPE: tall, otherwise typical
COGNITION: 
- reduced verbal IQ to low-normal range
- mild motor and language delay
- reading difficulties
BEHAVIOR:
- higher rates of ADD and ASD
FERTILITY:
- normal
27
Q

22q11.2 deletion syndrome: classic triad

A
  • conotruncal cardiac abnormalities
  • hypoplastic thymus
  • hypocalcemia
28
Q

Cri-du-Chat syndrome

  • cause
  • incidence
A

CAUSE:
- interstitial or terminal deletion of part of short arm of chr 15

INCIDENCE:

  • 1:15,000
    • 85% of cases are de novo
    • 10-15% of carriers are offspring of translocation carriers involving 5p
29
Q

Wolf-Hirschorn syndrome

  • incidence
  • cause
A

INCIDENCE: 1/50,000

CAUSE: partial deletion of 4p16.3

  • de novo in 87% of cases
  • 80% involve paternal chromosome
30
Q

Wolf-Hirschorn syndrome features

A

PHENOTYPE:

  • microcephaly, “Greek warrior helmet”, hypertelorism, glabella, high arched eyebrows, downturned corners of mouth
  • intellectual disability

OTHER FEATURES:

  • pre and postnatal growth restriction
  • congenital heart disease (ASD, VSD, PS)
  • antibody deficiencies
  • feeding difficulties
31
Q

Charcot-Marie-Tooth disease

  • cause
  • management
A

a demyelinating motor-sensory neuropathy characterized by progressive distal neuromuscular weakness with onset in 1st or 2nd decade of life

CAUSE: 1.5 Mb duplication of 17p11.2, including PMPP2 gene

MANAGEMENT:

  • rehab (stretching and strengthening)
  • avoid drugs that can worsen neuropathy
32
Q

Cri-du-Chat syndrome phenotype

A

PHENOTYPE:

  • cry sounds like cat at birth
  • FACE: round face, hypertelorism, epicanthal folds, low set ears, broad nasal bridge
  • HEAD/NECK : microcephaly
  • severe developmental delay and intellectual disability
  • hypotonia
  • low birth weight, failure to thrive
33
Q

Charcot-Marie-Tooth disease

- clinical presentation

A

frequent sprained ankle due to distal muscle weakness
foot drop
pes carvus
distal muscle wasting - “stork leg deformity’
paresthesias

34
Q

Turner Syndrome

  • cognition
  • behavior
  • fertility/reproductive health
A

COGNITION:
- Typically normal; Decreased spatial perception

BEHAVIOR:
- typically normal, may have impaired social adjustment

FERTILITY:

  • gonadal dysgenesis
  • primary amenorrhea
  • infertility

MedGen (3 decks)

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