Medically Fit For Exams
Medically Fit For Exams

Down's Syndrome

Definition

  • Trisomy 21

 

Risk factors

  • Advanced maternal age: >45 = 1/50, <29 = 1/1500
  • Parents have Down’s syndrome, females with Down’s syndrome have 50% chance of having an affected child
  • A screening-generated risk of 1 in 150 or greater is considered ‘high risk’

 

Differential diagnosis

  • None relevant

 

Epidemiology

  • Most common autosomal abnormality – 1 in 800 live births
  • Incidence is decreasing
  • No difference in incidence between races

 

Aetiology

  • Can be result of a non-disjunction event in meiosis (1st division or second division) – 94%
  • Can be translocation – part of 21 becomes attached to another chromosome – 4%
  • Moaicism – only some cells have trisomy 21 – 2%
  • Advances maternal age increases risk because the egg cells remain ‘paused’ halfway through meiosis until just before release at ovulation. The longer the pause, the higher the risk.

 

Clinical features

  • Facial
    • Epicanthal folds
    • Brushfield’s spots (white spots in eyes)
    • Large tongue, small mouth
    • Small nose, flat bridge
  • Head
    • Excess skin at the back of the neck (nuchal fold)
    • Brachycephaly (broad, flat back of head)
  • Hands
    • Broad, short fingers
    • Single palmar crease
    • Curved little finger
  • Feet
    • Sandal gap (large gap between hallux and second toe)
  • General physical
    • Low muscle tone
    • Hyperflexibility
    • Low birth weight and length
  • Heart – abnormality in 50%
    • Atrioventricular septal defect
    • Ventricular septal defect
    • Persistent ductus arteriosus
    • Tetralogy of Fallot
      • Overriding aorta (misaligned aorta)
      • Ventricular septal defect
      • Pulmonary artery stenosis
      • Right ventricular hypertrophy
  • Intellectual/cognitive
    • Reduced IQ – 20-85, 50% have IQ above 50 (70-85 and above is considered ‘low normal’)
    • Learning disability
  • Hearing problems – 75%
  • Eyesight problems – 60%
  • Thyroid problems – 15-20%
  • Leukaemia -1%

 

Pathophysiology

  • See aetiology

 

Investigations

  • Screening
    • Combined test 10-14 weeks – blood test for pregnancy hormones and nuchal translucency ultrasound (about 2-2.5mm is normal), also factors in mothers age
    • Quadruple test 14-20 weeks– 4 pregnancy hormones, also mothers age, weight and ethnicity
    • Harmony blood test – not available on the NHS, about £500, but highly accurate, about 99%, tests for foetal DNA
  • Diagnostic tests
    • Amniocentesis – needle sample of amniotic fluid, carries 1% risk of miscarriage, tests foetal DNA
    • Chorionic villus sampling – needle sample of placenta, carries 1-2% risk of miscarriage, tests foetal DNA

 

Management

  • Paediatrician
  • Cardiologist
  • Physiotherapist
  • Speech and language therapist
  • Portage worker (developmental play)
  • Special education school

 

Prognosis

  • Life expectancy is about 60
  • 40% have dementia at ages 50-59
Down's syndrome.docx
Microsoft Word document [14.9 KB]

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