Down's Syndrome (Trisomy 21)

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PatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.

See also: Prenatal Screening and Diagnosis of Down's Syndrome written for patients

Down's syndrome is a common genetic disorder characterised by learning difficulty, dysmorphic facial features and a host of structural abnormalities. It is named after John Langdon Haydon Down - an English physician, 1828-1896.


One of the most common genetic disorders, affecting 1 in 650-1,000.[1]

  • The underlying genetic defect is trisomy 21 in 94% of cases.
  • Mosaicism (2.4%) and translocations (3.3%) also occur.
  • 75% of these translocations are de novo errors.

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Risk factors

  • Family history.
  • Age of mother:
    • 1:385 risk at 35 years
    • 1:106 at 40 years
    • 1:30 at 45 years

At birth there is a wide range of associated physical features. Not all babies have typical facies. Frequently the first feature noticed is hypotonia.

Neonatal features of Down's syndrome

  • General:
    • Hyperflexibility.
    • Muscular hypotonia.
    • Transient myelodysplasia of the newborn.
  • Head:
    • Brachycephaly.
    • Oblique palpebral fissures.
    • Epicanthic folds.
    • Ring of iris speckles - Brushfield's spots.
    • Ears set low, folded or stenotic meatus.
    • Flat nasal bridge.
  • Mouth:
    • Protruding tongue (small narrow palate).
    • High arched palate.
  • Neck:
    • Loose skin on nape of neck.
  • Hands:
    • Single palmar crease.
    • Short little finger.
    • In-curved little finger.
    • Short broad hands.
  • Feet:
    • Gap between hallux and second toes.
  • Congenital heart defects.
  • Duodenal atresia.

Soon after birth all babies with Down's syndrome should be assessed for congenital heart disease by echocardiogram.[2] They should also have auditory evoked potential testing (before age 6 months) to check for hearing loss[3] and also be checked for congenital cataracts and glaucoma.[4]

Both children and adults with Down's syndrome will often need regular reviews with regard to specific associated conditions (see below). People with Down's syndrome should also have an annual review to include an assessment of feeding, bowel and bladder function, any behavioural disturbance, vision and hearing, and any other health concern.

Cardiological disorders

The most common cardiac abnormalities are:

Adult patients, without known congenital heart disease, may develop mitral valve prolapse or aortic regurgitation. A second assessment in early adulthood may be appropriate.

Ear, nose and throat disorders

  • 90% of patients with Down's syndrome may have conductive, sensorineural, or mixed hearing loss.[1]
  • They are more susceptible to otitis media, sinusitis and pharyngitis.
  • Obstructive sleep apnoea may develop.

Ophthalmological disorders

Most commonly:

Gastrointestinal disorders

Orthopaedic disorders

  • Atlanto-axial instability*.
  • Hyperflexibility.
  • Scoliosis.
  • Hip dislocation after two years.
  • Patellar subluxation or dislocation.
  • Foot deformities.

*Few need treatment.[7] They present with neck pain, limited movements or symptoms/signs suggestive of cord compression. Less specific symptoms - eg, bladder problems, gait abnormalities or clumsiness - may also indicate need for further investigation.

Endocrine disorders

These are common, particularly hypothyroidism. Annual TFTs are indicated.[8]

Neurological and psychiatric disorders

  • Learning difficulties (these range from severe, to those with 'low normal' IQ).
  • Behavioural problems.
  • Seizures occur in 5-10%.
  • In older patients an Alzheimer's-type picture develops in >60% of those over 60 years of age.

Haematological disorders

  • The prognosis for people with Down's syndrome depends on the nature and severity of any associated conditions.
  • Life expectancy is improving, especially because of improved diagnosis and management of those people with Down's syndrome who also have congenital heart defects.[1] 
  • At least half of people with Down's syndrome now live into their 50s and 60s.

This is covered in detail in the separate article on Antenatal Screening for Down's Syndrome.

Further reading & references

  1. Down Syndrome; Online Mendelian Inheritance in Man (OMIM)
  2. Basic medical surveillance essentials for people with Down's Syndrome: cardiac disease - congenital and acquired; Down's Syndrome Medical Interest Group (2007)
  3. Basic medical surveillance essentials for people with Down's Syndrome: hearing impairment; Down's Syndrome Medical Interest Group (2007)
  4. Basic medical surveillance essentials for people with Down's syndrome: ophthalmic problems; Down's Syndrome Medical Interest Group (2006 - Ophthalmic problems revised 2012)
  5. A Step by Step Guide for GP Practices: Annual health checks for people with a learning disability; Royal College of General Practitioners (2010)
  6. Weijerman ME, de Winter JP; Clinical practice. The care of children with Down syndrome. Eur J Pediatr. 2010 Dec;169(12):1445-52. Epub 2010 Jul 15.
  7. McKay SD, Al-Omari A, Tomlinson LA, et al; Review of Cervical Spine Anomalies in Genetic Syndromes. Spine (Phila Pa 1976). 2011 Oct 29.
  8. Basic medical surveillance for people with Down's Syndrome: thyroid disorder; Down's Syndrome Medical Interest Group (2001)

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Dr Hayley Willacy
Current Version:
Peer Reviewer:
Dr Adrian Bonsall
Document ID:
2071 (v23)
Last Checked:
Next Review:

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