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Edwards syndrome

Also known as: Trisomy 18, 18+ syndrome

Background

Edwards syndrome is a chromosome abnormality where the child has an extra chromosome 18 in every cell. It is a rare disorder, seen in about 1 in 4,400 live births.

There are three types of the syndrome:

  • Full form - in this form, every cell in the body has three chromosome 18s instead of two (94 per cent of cases).
  • Mosaic form - in this form, some cells have two chromosome 18s while others have three. The extent and severity of the condition will depend upon the ratio of normal to abnormal cells.
  • Partial form - in some cases there may be an extra copy of part of chromosome 18. This is referred to as 'partial trisomy 18'. The effects of this may be milder and would require further specialist advice.

Children with the full form do not often survive beyond infancy, with about 10 in 100 (10%) expected to live past one year of age. Those affected by the mosaic and partial forms may sometimes survive into adulthood.

Credits

Medical text written October 2010 by Dr Kate Baker, Specialty Registrar in Clinical Genetics, Addenbrookes Hospital, Cambridge, UK and Dr Nora Shannon. Last updated November 2016 by Dr Nora Shannon, Consultant Clinical Geneticist, Nottingham University Hospital, Nottingham, UK.

Although great care has been taken in the compilation and preparation of all entries to ensure accuracy, we cannot accept responsibility for any errors or omissions. Any medical information is provided is for education/information purposes and is not designed to replace medical advice by a qualified medical professional.

What are the symptoms?

Characteristic features can include:

  • feeding problems in infancy, leading to poor growth
  • structural heart defects, present in 90 per cent of individuals
  • abdominal wall defects and hernias (protrusion of organs and tissues through a gap in the abdominal wall)
  • low-set and simple ears
  • long fingers, small fingernails, clenched hands
  • smooth, rocker-bottom feet
  • pauses in breathing (apnoeas)
  • severe learning disability.

How is it diagnosed?

Edwards syndrome is often detected during pregnancy (see prenatal diagnosis) and some parents opt not to continue the pregnancy. In about 30 per cent of cases (higher for affected males than females), a spontaneous miscarriage occurs.

Sometimes a baby may be born with features of Edwards syndrome after normal scans in the pregnancy. In this situation, a blood sample from the baby will be sent for karyotype analysis to confirm the diagnosis.

How is it treated?

Parents should meet with the obstetric and neonatal teams to discuss the diagnosis and to prepare for delivery and the care of their baby. It is likely that the baby will be admitted to the special care baby unit, and will require supportive treatments over the first days of life.

Many babies with Edwards syndrome have a structural heart problem (see entry Heart Defects). Babies are likely to require long-term nasogastric tube feeding, and may be more comfortable if they are given medicine to prevent gastro-oesophageal reflux. In addition, these babies may also need help with breathing.

Sadly, about half of babies born with Edwards syndrome do not survive longer than one week, with about 10 in 100 expected to live past one year of age. If a baby is well enough to leave hospital, community support arrangements should be put in place, and follow-up plans made with the local paediatric team.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
Edwards syndrome usually occurs as a "one-off" (sporadic), and therefore it is extremely unlikely that parents will have more than one pregnancy affected by Edwards syndrome. In rare cases, a balanced translocation in a parent can give rise to an unbalanced translocation in their child leading to a higher risk in the next pregnancy. This situation is detected on the baby's karotype.

Prenatal diagnosis
Women are offered a combined blood test and scan between 12 to 14 weeks into a pregnancy to screen for Down's syndrome. These tests have recently been changed to report a risk for Edwards syndrome. If a high risk is detected a chorionic villous sample or amniocentesis is offered which can diagnose Edwards syndrome.

Routine ultrasound scanning at 18 to 20 weeks can detect physical features of Edwards syndrome in over 70 per cent of cases. If an ultrasound scan suggests a high risk of a chromosome problem, a definitive genetic test to look at the baby's chromosomes will be discussed.

Is there support?

SOFT UK

Tel: 0121 351 3122
Email: enquiries@soft.org.uk
www.soft.org.uk

The Organisation is a Registered Charity in England and Wales No. 1002918. It provides information and support for families affected by Trisomy 13 (Patau's Syndrome), Trisomy 18 (Edwards' Syndrome) and related disorders, including prenatal information and bereavement support. 

Group details last updated November 2016.

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