Synonym: trisomy 21
It 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.
- 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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- 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 (most common features first)
- Oblique palpebral fissures.
- Gap between hallux and second toes.
- Loose skin on nape of neck.
- Ears set low, folded or stenotic meatus.
- Protruding tongue (small narrow palate).
- Flat nasal bridge.
- Muscular hypotonia.
- Epicanthic folds.
- Ring of iris speckles - Brushfield's spots.
- Short little finger.
- In-curved little finger.
- Short broad hands.
- High arched palate.
- Single palmar crease.
- Congenital heart defects.
- Transient myelodysplasia of the newborn*.
- Duodenal atresia*.
Soon after birth all babies with Down's syndrome should be assessed for congenital heart disease by echocardiogram. They should also have auditory evoked potential testing (before age 6 months) to check for hearing loss and also be checked for congenital cataracts and glaucoma.
The most common cardiac abnormalities are:
- Atrioventricular canal defects.
- Ventricular septal defect.
- Isolated secundum atrial septal defects.
- Isolated persistent patent ductus arteriosus.
- Fallot's tetralogy.
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.
- They are more susceptible to otitis media, sinusitis and pharyngitis.
- Obstructive sleep apnoea may develop.
- Refractive errors
- Congenital glaucoma
- Oesophageal atresia or tracheo-oesophageal fistula.
- Duodenal atresia.
- Pyloric stenosis.
- Meckel's diverticulum.
- Hirschsprung's disease.
- Imperforate anus.
- Gastro-oesophageal reflux.
- Dental problems - delayed and unusual patterns of eruption, missing teeth.
- Coeliac disease occurs frequently enough for screening to be recommended.
- Atlanto-axial instability*.
- Hip dislocation after two years.
- Patellar subluxation or dislocation.
- Foot deformities.
*Few need treatment. 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.
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.
- Patients have approximately 12 x greater risk of infections, eg pneumonia due to impaired cellular immunity.
- They also have increased risk of acute myeloblastic leukaemia (AML), acute lymphoblastic leukaemia (ALL) and acute megakaryoblastic leukaemia (AMegL).
- Polycythaemia and transient myeloproliferative disorder (a self-limiting type of leukaemia which regresses spontaneously by the age of two months) may occur in newborns.
Prenatal screening and diagnosis
This is covered in detail in Antenatal Screening for Down's syndrome.
Further reading & references
- Antenatal care: routine care for the healthy pregnant woman, NICE Clinical Guideline (March 2008)
- Standards and Policies, NHS Fetal Anomaly Screening Programme
- Down Syndrome, Online Mendelian Inheritance in Man (OMIM)
- Chen H, Genetics of Down Syndrome, Medscape, Feb 2011
- Basic medical surveillance essentials for people with Down's Syndrome: cardiac disease - congenital and acquired, Down's Syndrome Medical Interest Group (2007)
- Basic medical surveillance essentials for people with Down's Syndrome: hearing impairment, Down's Syndrome Medical Interest Group (2007)
- Basic medical surveillance essentials for people with Down's syndrome: ophthalmic problems, Down's Syndrome Medical Interest Group (2006)
- 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.
- McKay SD, Al-Omari A, Tomlinson LA, et al; Review of Cervical Spine Anomalies in Genetic Syndromes. Spine (Phila Pa 1976). 2011 Oct 29.
- Basic medical surveillance for people with Down's Syndrome : thyroid disorder, Down's Syndrome Medical Interest Group (2001)
|Original Author: Dr Hayley Willacy||Current Version: Dr Hayley Willacy||Peer Reviewer: Dr Hannah Gronow|
|Last Checked: 14/12/2011||Document ID: 2071 Version: 22||© EMIS|
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