Paediatrics: Down syndrome

Down syndrome

Incidence 

71 in 600–700 live births (incidence increases with advancing maternal age).

Cause

The great majority (795%) of babies with Down syndrome have trisomy 21, usually due to non-disjunction during maternal oogenesis. 72% are the result of a Robertsonian translocation. 72% are mosaic, with a normal cell line as well as the trisomy 21 cell line.

Clinical features

•   Usually presents at birth.

•   Generalized hypotonia and marked head lag.

•   Facial features: small low-set ears, up-slanting eyes, prominent epicanthic folds, a flat facial profile, protruding tongue. Later Brushfield’s spots apparent in the iris (whitish spots).

•   Flat occiput (brachycephaly) and short neck.

•   Typical limb features: short broad hands (brachydactyly), short incurved little fingers (clinodactyly), single transverse palmar crease, and a wide ‘sandal’ gap between the first and second toes.

•   Mildly short stature.

•   Intellectual impairment becomes apparent. IQ scores range from 25 to 70.

•   Social skills often exceed other intellectual skills.

Associated conditions

•   740–50% have congenital heart disease, most commonly atrio-ventricular septal defect (AVSD), ASD, VSD, Fallot tetralogy.

•   GI problems include: duodenal atresia, anal atresia, HSD.

•   Increased risk of infection.

•   Developmental hip dysplasia.

•   Eczema.

•   Deafness: both sensorineural and conductive.

•   Cataracts.

•   Leukaemia (1%).

•   Acquired hypothyroidism.

Diagnosis

If there is clinical suspicion of Down syndrome, a senior paediatrician should discuss their concerns with the parents. The diagnosis is confirmed by a chromosome analysis showing an additional chromosome 21. Most cytogenetics laboratories are able to offer a rapid analysis, e.g. interphase FISH, in order to establish the diagnosis quickly.

Management

·Refer for a detailed cardiac assessment, hip US, and audiology.

• Genetic counselling by a clinical geneticist should be offered. It is not necessary to undertake parental chromosome analysis if the cause is non-disjunctional trisomy 21 or mosaic trisomy 21, but this is very important if the karyotype shows a translocation.

• Putting the parents in contact with a support organization, such as the Down Association, is often helpful (M www.downs-syndrome.org.uk and M www.ndss.org).

• Long-term follow-up should ideally be by a multidisciplinary team led by a paediatrician with special expertise, such as a developmental paediatrician, working in a child development centre. Physiotherapy to improve tone and posture is often required.

• Routinely test TFT annually.

• Refer for audiology and ophthalmic assessment 1–2-yearly.

• Almost all children with Down syndrome are now educated in mainstream schools with appropriate educational support.

Prognosis

If deaths from congenital cardiac disease are excluded, life expectancy is well into adult life, although somewhat shortened as almost all develop Alzheimer disease by age 40yrs. Majority of adults can live semi-indepen-dently with supervision.