A CASE OF POSSIBLE TRISOMY 21

Dysmorphology is the study of human congenital malformations and dysmorphic features are abnormal body characteristics. Some are common in the general population and in isolation are not significant, e.g. single palmar crease. A syndrome is a well-characterized group of such abnormalities occurring together that often point to a single condition as the cause.

Characteristic dysmorphic features of trisomy 21

• Hypotonia

• Flat face

• Upward slanting palpebral fissures

• Epicanthic folds

• White speckles in the iris (Brushfield spots)

• Short broad hands

• Single palmar and plantar fissures (Simian crease)

There are several associated features, the commonest of which are low IQ (average IQ about 50), congenital heart disease, duodenal atresia and short stature. Chromosomes must be sent for urgent analysis. This is to confirm the clinical suspicions, look for mosaicism (1 per cent) that might alter the prognosis and to exclude a translocation. If a translocation is identified, parental chromosomes must be analysed in case one is a carrier with a high risk of recurrence. The incidence of cardiac anomalies is so high (35 per cent) that all children with trisomy 21 should have a cardiac echocardiogram even if no murmur is detected. An atrioventriculoseptal defect (AVSD) is the characteristic association with trisomy 21, but a ventriculoseptal defect is the commonest abnormality. Although the risk of Down’s syndrome rises with maternal age, most mothers of children with Down’s syndrome are 30 years as this is the group that has the greatest number of children. Breaking bad news is never easy but parents will always remember the first discussion. They should be seen by a senior paediatrician with the midwife who knows them well and other family members if they wish. If English is not their first language, an interpreter should be supplied – this should not be a family member as this person needs to be impartial. The discussion should take place in a private room with no phones or bleeps and plenty of time should be allowed. Avoid jargon and use diagrams to help explanations. It is worth exploring if they have noticed anything. Expect distress, anger, guilt, shame – in fact, any emotion. They are likely to ask how this could happen when they were given a negative screen result. There is a very common misconception amongst the public and professionals that a negative screen completely excludes the diagnosis. Antenatal screening programmes identify those at high risk to whom a definitive diagnostic test (e.g. amniocentesis) should be offered.

Acknowledge that it is normal to forget much of this first meeting. Arrange another meeting soon afterwards and suggest they write down any questions that arise in the meantime. Written material is available from Down’s syndrome charities and their websites.

KEY POINTS

• Negative antenatal screening does not mean zero risk.

• Chromosomes must always be analysed even if the clinical findings are absolutely characteristic of a syndrome.