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Down Syndrome

Down Syndrome

Down syndrome is a congenital disorder resulting from an extra copy (trisomy) of chromosome 21. 

The mechanisms by which increased dosage of genes on chromosome 21 leads to Down syndrome are as yet unknown.  However, neuropathological changes associated with dementia in Down syndrome are typical of Alzheimer’s disease.

Epidemiology

  • Incidence: 1/650-1/1000
  • All ethnic groups
  • Male = Female

Clinical Presentation

Clinical features are variable. Trisomy 21 may present pre- or post-natally.

Pre-natal:

  • Miscarriage
  • Abnormal maternal serum screening, increased hCG, inhibin-A.
  • Ultrasound scanning: increased nuchal translucency, nasal bone hypoplasia, cardiac defect, double stomach bubble (secondary to duodenal atresia).

Post-natal:

  • Hypotonia and feeding problems in infancy
  • Dysmorphism
  • Congenital anomalies, particularly congenital heart defects

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Physical Signs

  • Dysmorphism
  • Upslanting palpebral fissures, epicanthic folds, Brushfield spots
  • Protruding tongue
  • Brachycephaly
  • Single palmar creases, clinodactyly, sandal gap
  • Evidence of congenital heart defect
  • Evidence of gastrointestinal obstruction

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Complications

  • Congenital heart defects (40-50%), VSD is the most common, followed by AVSD, ASD, PDA and Tetralogy of Fallot.
  • Short stature
  • Hypothyroidism (20-40%)
  • Diabetes mellitus (1%)
  • Leukaemia, especially ALL (2%)
  • Obstructive sleep apnoea
  • Duodenal atresia/ stenosis, hirschsprung disease
  • Behavioural problems (10%)
  • Seizures (8%)
  • Dementia, mean age 50yrs+
  • Atlantoaxial subluxation (15% on X-ray, few symptomatic)
  • Eyes (refractive errors)
  • Learning difficulties, average IQ 45-48, adults will require daily supervision.

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