Down syndrome was first described by Dr John Langdon Down in 1886. Despite the availability of improved antenatal diagnosis, the incidence of Down syndrome remains at around 1 in 1,100 births.
The risk of Down syndrome increases with maternal age, and this is the most important risk factor.
In Victoria women are offered maternal serum screening between nine and 13 weeks combined with ultrasound for Nuchal translucency at 11-13 weeks to establish their risk of Down syndrome with 80-90 per cent sensitivity (however, this means that 10-20 per cent of women with a 'negative' test may still have a baby with Down syndrome).
Despite these measures babies with Down syndrome are born unexpectedly and many of these are born to women under 35 years.
It is usually possible to make a confident clinical diagnosis in a term newborn on the basis of a combination of dysmorphic features.
A range of well-known physical findings, some less specific than others, are described; however, no single physical abnormality is 100 per cent specific for Down syndrome and the gold standard for diagnosis remains the banded karyotype.
The phenotype may not be appreciated in preterm infants. If suspected a thorough examination plus karyotype is required.
Image courtesy Stanford Medicine, Newborn Nursery.
Most frequent findings are:
- upslanting palpebral fissures
- ear abnormalities
- epicanthic folds
- flat facial profile
- sandal sign with increased space between first and second toes
- single palmar crease (simian crease).
Image courtesy Medical Genetics, Mosby, Jord, Carey, Bamshad, White.
- Protruding tongue
- those with mosaic Down syndrome (where some cells have Trisomy 21 and others a normal complement/number of chromosomes) may have no dysmorphic features, and go unrecognised. Mosaic Down syndrome accounts for only 2-4% of cases of Down syndrome.
Associated neonatal health issues
Associated health issues important to the early neonatal period include:
- cardiac defects (30-40 per cent) particularly atrioventricular septal defects
- tetralogy of Fallot
- gastroenterological (12 per cent)
- oesophageal atresia
- duodenal atresia
- imperforate anus
- Hirschsprung disease
- congenital optic lens opacities (3 per cent)
- congenital hip dysplasia spectrum
- thyroid problems, including athyrosis
- intellectual impairment
- feeding difficulties.
Investigations for Down syndrome:
- Chromosomal analysis should be performed whenever the diagnosis of Down syndrome is seriously suspected.
- The karyotype can be performed after birth on cultured lymphocytes from a blood sample (lithium heparin blood 2-5 mL). Routine blood karyotype takes 10-14 days to complete and an urgent karyotype result is unlikely to be available inside seven days.
- Fluorescent in-situ hybridisation (FISH) using a probe specific for the Down syndrome critical region can be processed in 48 hours when an urgent result is required. Direct communication with the on-call genetics fellow or the scientist in the cytogenetics laboratory will facilitate the laboratory confirmation of Down syndrome.
- Given the frequency of cardiac defects, an echocardiogram is recommended as a routine.
- Formal thyroid function tests should be requested to exclude congenital hypothyroidism.
- Other investigations may be required, depending on clinical concerns.
If a diagnosis of Down syndrome is suspected, discussion with both parents as to the likelihood of Down syndrome, on clinical grounds, should occur as soon as possible.
Sufficient time should be made available for what is often, initially, a distressing diagnosis. It is advisable that, if possible, a midwife and social worker be present.
If experienced staff consider that the diagnosis of Down syndrome is likely, an urgent T21 FISH should be obtained. A follow-up discussion with the family should occur once the FISH result is available.
The clinical genetics service is happy to be involved in counselling the parents. (Victorian Clinical Genetics Services (VCGS))
Once the diagnosis is made, repeated counselling will be required as this is a life-long condition and the impact of the diagnosis will result in a difficult time for parents and family. Parents often work through the diagnosis and its impact at different rates.
Life-threatening cardiac and gastrointestinal defects will require urgent management and consultation with the relevant on-call sub-specialist(s), and PIPER.
By comparison, when a newborn has significant dysmorphic features not typical of Down syndrome, it is advised that the parents be informed of the atypical physical features and that a karyotype will be requested to exclude a chromosomal abnormality.
Referral for an early cardiology and ophthalmology consultation should be organised prior to discharge as should early follow-up with a general paediatrician and the family's general practitioner. Early childhood intervention should also be arranged.
The Down Syndrome Association of Victoria offer considerable support and information, including a folder containing suitable information for parents of newly diagnosed children as well as a folder for health professionals.
Differential diagnosis for Down syndrome involves:
- Smith-Maginnis syndrome (deletion of chromosome material from chromosome 17)
- Zellweger syndrome (presents in newborn period with hypotonia and feeding problems, infants rarely survive beyond one year).
Areas of uncertainty
A range of non-mainstream therapies to assist with development have been recommended by various individuals and groups.
A discussion regarding these practices is outside the scope of this topic.
Clinical information and support services
- Down Syndrome Victoria
- Victorian Clinical Genetics Services
- Down Syndrome Australia
- Royal Children's Hospital - Screening for children with Down syndrome
- Down Syndrome Victoria - Referral form
- Devlin L, Morrison PJ. Accuracy of the clinical diagnosis of Down Syndrome; Ulster Med J. 2004 May: 73(1): 4-12
- Fried K. A score based on eight signs in the diagnosis of Down Syndrome in the Newborn; J Ment Defic Res. 1980 Sep; 24(3):181-5
- Gardner RJM and Sutherland GR: Chromosome Abnormalities and Genetic Counselling (3rd Edition). 2004 (Oxford University Press)
- Hall B. Mongolism in newborn Infants. An examination of the criteria for recognition and some speculations on the pathogenic activity of the chromosomal abnormality; Clin Pediatr (Phila). 1966 Jan 5(1): 4-12
- Hunter AGW: Down Syndrome in Management of Genetic Syndromes (2nd Edition), Edited by Cassidy SB and Allanson JE. 2005 (John Wiley and Sons)
- Kava MP, Tullu Ms, Muranjan MN, Girisha KM. Down Syndrome: Clinical profile from India; Arch Med Res. 2004 Jan- Feb; 35(1) 31-5
- Smith's Recognizable Patterns of Human Malformation 6th Ed. W.B Saunders Company 1977
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First published: November 2016
Last web update: October 2018
Review by: November 2019
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Page last updated: 12 Nov 2020