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CP2 Paeds - Genetics and syndromes > Syndromes > Flashcards

Syndromes Flashcards

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1
Q

What is down syndrome?

A

Trisomy 21, most common autosomal trisomy and most common genetic cause of severe learning difficulties.

Incidence in live-born infants is about 1 in 650 and increases with maternal age

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2
Q

Clinical features of down syndrome

A
  • round face and flat nasal bridge
  • upslanted palpebral fissures
  • epicanthic folds
  • pigmented spots in iris
  • small mouth and protruding tongue
  • small ears
  • flat occiput and third fontanelle
  • short neck
  • single palmar crease
  • incurved and short fifth finger
  • wide sandal gap between 1st and 2nd toes
  • hypotonia
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3
Q

Neonatal complications of down syndrome:

A
  • congenital heart disease is present in 40%
  • duodenal atresia
  • Hirschsprung disease <1%
  • learning difficulties - varies widely
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4
Q

Prognosis of down syndrome:

A
  • over 85% of infants survive to 1 year

- at least 50% of affected individuals live longer than 50 years

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5
Q

What should children with down syndrome be screened for?

A

Hearing/vision impairments, hypothyroidism, coeliac disease, atlantoaxial instability

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6
Q

Cytogenics of down syndrome?

A
  • meiotic nondisjunction - 94%
  • translocation - 5%
  • mosaicism - 1%
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7
Q

What is meiotic nondisjunction trisomy 21?

A
  • error at meiosis
  • the chromosome 21 pair fails to separate so one gamete has 2 cr21 and one has none
  • fertilisation of gamete with 2 cr21 gives rise to zygote with trisomy 21
  • parental chromosomes do not need to be examined
  • risk increases with increased maternal age, but more common in younger mothers as larger proprotion
  • can occur in spermatogenesis
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8
Q

What is translocation trisomy 21?

A
  • when the extra chromosome 21 is joined onto another chromosome (usually 14 but can be 15,21,22 - Robertsonian)
  • parental chromosome analysis is recommended
  • risk of recurrence is 10-15% if the mother is translocation carrier
  • risk of recurrence is 2.5% if father is carrier
  • if parent carries the rare 21:21 translocation all offspring will have down syndrome
  • if neither parent carries translocation (75%) the recurrence risk is <1%
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9
Q

What is mosaicism trisomy 21?

A

Some cells are normal and some have trisomy 21. Milder down syndrome

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10
Q

Diagnostic investigations for down syndrome?

A
  • rtPCR/FISH analysis of blood
  • antenatal screening tests measuring biochemical markers in blood samples and nuchal thickening on USS
  • amniocentesis if increased risk identified
  • non-invasive prenatal testing - maternal blood analysed, part of routine screening can opt out
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11
Q

Later medical problems in down syndrome:

A
  • delayed motor milestones
  • learning difficulties
  • short stature
  • increased susceptibility to infections
  • hearing impairment from secretory otitis media (75%)
  • visual impairment from cataracts (15%), squints, myopia (50%)
  • increased risk of leukaemia and solid tumours (1%)
  • acquired hip dislocation/atlantoaxial instaiblity
  • obstructive sleep apnoea (50%-75%)
  • increased risk of hypothyroidism (15%) and coeliac disease
  • epilepsy
  • early onset Alzheimer’s disease
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12
Q

What is Edwards syndrome?

Incidence?

A

Trisomy 18

1 in 8000 live births

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13
Q

Clinical features of Edwards syndrome?

A
  • low birthweight
  • prominent occiput
  • small mouth and chin
  • short sternum
  • flexed, overlapping fingers
  • ‘rocker bottom’ feet
  • cardiac and renal malformations
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14
Q

What is Patau syndrome?

Incidence?

A

Trisomy 13

1 in 14 000 live births

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15
Q

Clinical features of Patau syndrome?

A
  • structural defect of brain
  • scalp defects
  • small eyes and other eye defects
  • cleft lip and palate
  • polydactyly
  • cardiac and renal malformations
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16
Q

What is Turner syndrome?

Incidence?

A

Only occurs in females: 45, X
1 in 2500 live born females
>95% results in early miscarriage

17
Q

How can Turner syndrome be identified antenatally?

A

USS showing fetal oedema of neck, hands, or feet and cystic hygroma may be identifies

18
Q

Clinical features of Turner syndrome?

A
  • lymphoedema of hands and feet in neonate which may persist
  • spoon-shaped nails
  • short stature
  • neck webbing/thick neck
  • wide carrying angle
  • widely spaced nipples
  • congenital heart defects (particularly CoA)
  • delayed puberty
  • ovarian dysgenesis resulting in infertility, although pregnancy may be possible with IVF using donated ova
  • hypothyroidism
  • renal anomalies
  • pigmented moles
  • recurrent otitis media
  • normal intellectual function in most cases
19
Q

Cytogenetics of Turner syndrome?

A
  • 50% have 45, X
    Other cases:
  • deletion of short arm of one X chromosome
  • Isochromosome that has 2 long arms but on short arm
  • Variety of other structural defects of X chromosomes
  • Presence of Y chromosome sequence may increase risk of gonadoblastoma
  • incidence does not increase with maternal age and risk of recurrence is very low
20
Q

Treatment of Turner syndrome?

A
  • growth hormone therapy
  • oestrogen replacement for development of secondary sexual characteristics at time of puberty

infertility still persists

21
Q

What is fragile X syndrome?

A

Inherited X-linked disorder
A break in the distal part of the long arm of the X chromosome causing significant learning difficulties in males (1 in 4000)
- 2nd most common genetic cause of severe learning difficulties

22
Q

Characteristics of fragile X syndrome?

A
  • mod-severe learning difficulty
  • macrocephaly
  • macroorchidism - postpubertal
  • long face, large everted ears, prominent mandible, broad forehead
  • mitral valve prolapse, joint laxity, scoliosis, autism, hyperactivity
23
Q

What is Marfan syndrome?
Clinical features?
Later risks?

A

Autosomal dominant disorder of connected tissue

Tall stature, long thin digits, hyperextensible joints, high arched palate, dislocation of lenses, severe myopia. May be chest deformity and scoliosis.

Major probs - cardiovascular: mitral valve prolapse and regurg; aneurysms of aorta may dissect or rupture

24
Q

What is Rett syndrome?

A

Rare genetic neurological and developmental disorder that affects the way the brain develops, causing progressive inability to use muscles for eye and body movements and speech.
Occurs almost exclusively in girls

Seem to develop normally at first but after 6months lose skills they previously had - crawling, walking, communicating, using hands

25
Q

What is Duchenne muscular dystrophy?

A

X-linked recessive disorder affecting 1 in 3000-6000 male live births.
Inherited, although 1/3 have de novo mutations
Progressive muscle degeneration

26
Q

Clinical presentation of DMD:

A

Average age of diagnosis is 5y, although children often become symptomatic much earlier

  • waddling gait and/or language delay
  • +ve Gowers sign (need to turn prone to rise)
  • pseudohypertrophy of calves
  • boys tend to be slower and clumsier than their peers
27
Q

Initial screening tests for DMD:

A
  • elevated creatine kinase

- DNA analysis

28
Q

Management of DMD:

A
  • physiotherapy to help prevent contractures with aid of splints
  • Tendoachilles lengthening and scoliosis surgery
  • overnight CPAP for nocturnal hypoxia
  • corticosteroids to preserve mobility and prevent scoliosis
  • Ataluren (drug) allows production of small amount od dystrophin
29
Q

Prognosis of DMD:

A
  • Progressive so many no longer ambulant by 10-14 years
  • life expectancy reduced to late 20s from resp failure or associated cardiomyopathy
  • 1/3 have learning difficulties
  • scoliosis common problem
30
Q

What is neurofibromatosis type 1?

A

NF-1 affects 1 in 3000 live births
Autosomal dominant, highly penetrant condition with variable expression
Caused by mutation in NF-1 gene which arises in about 50% as de novo mutation

31
Q

Diagnostic criteria of NF-1

A

2 or more need to be present of:

  • 6 or more café-au-lait spots greater than 5mm in size before puberty, greater than 15mm after puterty
  • more than one neurofibroma
  • axillary freckling
  • optic glioma which may cause visual impairment
  • one Lisch module
  • bony lesions from sphenoid dysplasia
  • first degree relative with NF-1
32
Q

What is NF-2?

A

multiple inherited schwannomas, meningiomas and ependymomas
AD caused by mutation in NF2 gene, usually presenting in adolescence

Bilateral acoustic neuromata are the predominant feature and present with deafness and sometimes facial nerve paresis and cerebellar ataxia

33
Q

What can NF-1 and NF-2 be associated with?

A
  • endocrinological disorders
  • multiple endocrine neoplasia syndromes
  • phaeochromocytoma
  • pulmonary hypertension
  • renal artery stenosis with htn
34
Q

What is tuberous sclerosis

A

Neurocutaneous syndrome caused by mutation of TSC1 or TSC2 genes
AD, occurs in 1 in 9000 live births, up to 70% de novo

35
Q

Cutaneous features of tuberous sclerosis:

A
  • depigmented “ash-leaf” shaped patches or amelanotic naevi which fluoresce under uv light
  • roughened patches of skin usually over lumbar spine
  • angiofibromata in a butterfly distribution over bridge of nose and cheeks, unusual before 3y
36
Q

Neurological features of tuberous sclerosis:

A

seen in 50% including:

  • infantile spasms and developmental delay
  • epilepsy - often focal
  • intellectual disability, often with autism
37
Q

Clinical features of achondroplasia?

A

AD genetic skeletal condition

  • short stature from marked shortening of the limbs
  • large head
  • frontal bossing
  • depression of nasal bridge
  • hands are short and broad
  • marked lumbar lordosis develops
  • sometimes hydrocephalus
38
Q

What is phetylketonuria?
diagnosis?
presentation if not detected/treated?
management?

A

inherited disorder that increases phenylalanine in the blood

heel prick test 1-2 days after birth
learning difficulties, seizures, microcephaly
phenylalanine restricted diet

39
Q

clinical features of fetal alcohol syndrome?

A
  • growth restriction
  • developmental delay
  • cardiac defects (up to 70%)

characteristic faces:

  • saddle-shaped nose
  • maxillary hypoplasia
  • absent philtrum between nose and upper lip
  • short, thin upper lip

CP2 Paeds - Genetics and syndromes (1 decks)

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