Down Syndrome

Background

  • Trisomy 21 (90%), Translocation 21 (5%), Mosaic 21 (5%)
  • Incidence: 1/800 live births in USA, M=F
  • Life expectancy mildly decreased

Diagnosis

  • Prenatally
    • Amniocentesis
    • Percutaneous umbilical blood sampling (PUBS)
    • Chorionic villus sampling (CVS)
    • Extraction of fetal cells from the maternal circulation
  • Physical features
    • Growth: short for age
    • Head: brachycephaly, microcephaly, a sloping forehead, a flat occiput, large fontanels with late closure
    • Eyes: up-slanting palpebral fissures, bilateral epicanthal folds, Brushfield spots (speckled iris)
    • Nose: flat nasal bridge
    • Mouth: relative macroglossia, micrognathia, high arched palate, open mouth with a tendency of tongue protrusion, a fissured and furrowed tongue, mouth breathing with drooling
    • Ears: ears are small with an overfolded helix; chronic otitis media and hearing loss are common
    • Neck: ligamentous laxity (atlanto-axial instability), short neck
    • CVS: murmur 2o to cardiac defects
    • Hands: single palmar crease
    • CNS: hypotonia, developmental delay
  • Chromosomal karyotype

Management

  • Identification
  • TSH
  • Cardiac US
  • Abdominal US for fever NYD (urinary tract abnormalities)
  • Neck X-ray for trauma/pain
  • Hearing tests
  • Eye exams

Complications

  • Hearing loss 66-75%
  • Congenital heart disease 50%
  • Lens opacities 59%, strabismus 33-45%, nystagmus 15-35%
  • Bowel obstruction 10% (duodenal atresia), Hirschprung’s 3%
  • Thyroid 5-8%
  • Alzheimer’s, Seizures, Leukemia

Follow up

  • Growth and development
    • Specific growth charts, milestones differ, early intervention program for hypotonia and developmental delay
  • Genetics – counselling for parents
  • Cardiac
    • Early evaluation as newborn, SBE prophylaxis may be necessary for certain cardiac diseases
  • Ophthalmologic
    • Early evaluation for cataracts and glaucoma, q6mo, then q2yr
  • ENT
    • Annual audiologic evaluation in first 3 years, then qyearly
  • Orthopedic
    • Atlantoaxial instability screening with X-rays in preschool years, then qdecade, especially before sporting events
  • Endocrine
    • Thyroid testing as newborn, 6 mo, 12 mo, then qyearly
  • Schooling
    • Early intervention programs
    • Not all children will have mental retardation, but most will

Chromosomal abnormalities

  • Non-disjunction
  • Robertsonian translocation: Two breaks occur in separate chromosomes, usually the 14th and 21st chromosomes. There is rearrangement of the genetic material so that some of the 14th chromosome is replaced by extra 21st chromosome. So while the number of chromosomes remain normal, there is a triplication of the 21st chromosome material.
  • Any translocation can cause it

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