Edwards’ syndrome
Introduction
Edwards’ syndrome, also known as trisomy 18, is a serious genetic condition caused by an additional copy of chromosome 18 in some or all of the cells in the body.
Each cell normally contains 23 pairs of chromosomes, which carry the genes you inherit from your parents, but a baby with Edwards’ syndrome has three copies of chromosome number 18, instead of two.
This disrupts the baby’s normal development and, in many cases, causes them to be miscarried or stillborn.
Babies with Edwards’ syndrome will have grown slowly in the womb and will have a low birthweight, along with a number of other serious medical problems. Of those that survive to birth, around half will die within two weeks and only around one in every five will live at least three months.
Around one in every 12 babies born with Edwards’ syndrome survive beyond one year, and they will live with severe physical and mental disabilities. Some children do survive to early adulthood, but this is very rare.
Edwards’ syndrome affects around one in 3,000 to 6,000 live births.
What are the features and symptoms?
Babies with Edwards’ syndrome can have a wide range of different problems.
Physical signs of Edwards’ syndrome include:
a small, abnormally shaped head
a small jaw and mouth
long fingers that overlap, with underdeveloped thumbs and clenched fists
low-set ears
smooth “rocker bottom” feet (with a rounded base)
a cleft lip and palate (a gap or split in the upper lip and/or the roof of the mouth)
an exomphalos (where the intestines are held in a sac outside the tummy)
Babies with Edwards’ syndrome also typically have:
heart and kidney problems
feeding problems – leading to poor growth
breathing problems
hernias in the wall of their stomach (where internal tissues push through a weakness in the muscle wall)
bone abnormalities – such as a curved spine
frequent infections of the lungs and urinary system
a severe learning disability
How does Edwards’ syndrome happen?
Edwards’ syndrome is rarely inherited and the condition is not caused by anything the parents have done.
The development of three copies of chromosome 18 usually happens randomly during the formation of eggs and sperm. There is an error in the division of cells, and the extra chromosome is either in the egg cell produced by the mother or in the sperm cell produced by the father.
As this happens randomly, it’s extremely unlikely for parents to have more than one pregnancy affected by Edwards’ syndrome.
The chance of having a baby with Edwards’ syndrome increases with the mother’s age.
Types of Edwards’ syndrome
There are two main types of Edwards’ syndrome.
Full form
Approximately 94% of babies with Edwards’ syndrome will have the full form, where every cell in their body has three copies of chromosome 18, instead of two. Most babies with this form will die before infancy.
Mosaic trisomy 18
About 5% of babies with Edwards’ syndrome will have the extra copy of chromosome 18 in only some of their body cells. This less severe form of the disease is known as mosaic trisomy 18.
The severity of mosaic trisomy 18 depends on the type and number of cells that have the extra chromosome. Some babies may only be mildly affected, while some can be severely disabled.
Around seven in every 10 babies born with mosaic trisomy will live for at least a year and, in rare cases, babies with the condition may survive into early adulthood.
Testing for Edwards’ syndrome during pregnancy
Pregnant women are offered screening for Edwards’ syndrome between 10 and 14 weeks of pregnancy to assess the chances of their baby having the condition.
The screening test, known as the combined test, comprises a blood test plus a nuchal translucency ultrasound scan (nuchal translucency is a collection of fluid at the back of the baby’s neck). This test also screens for Down’s syndrome and Patau’s syndrome.
Read more about screening for Edwards’ syndrome at 10-14 weeks.
Later in pregnancy, usually when you are 18 to 21 weeks pregnant, you will also be offered a scan that looks for physical abnormalities and 11 rare conditions, including Edwards’ syndrome.
Read more about the mid-pregnancy scan.
If the screening tests show that you have a higher risk of having a baby with Edwards’ syndrome, you will be offered diagnostic tests to find out for certain if your baby has the condition.
The diagnosis can be confirmed by carrying out chorionic villus sampling or amniocentesis. These are invasive tests performed during pregnancy to remove a sample of tissue or fluid so it can be tested for the presence of the extra copy of chromosome 18.
A newer test has also been developed that can be performed by taking a sample of blood from the mother and testing the baby’s DNA that is found within it. This is known as “non-invasive prenatal diagnosis” and is only available privately.
Read more about screening tests in pregnancy.
Is there any treatment?
There is no cure for Edwards’ syndrome and the symptoms can be very difficult to manage. You are likely to need help from a wide range of health professionals.
Treatment will focus on immediately life-threatening issues, such as infections and heart problems. Your child may also need to be fed through a feeding tube, if feeding is a problem.
If limb abnormalities affect your child’s movements as they get older, they may benefit from supportive treatment, such as physiotherapy and occupational therapy.
Depending on your child’s specific problems, they may need specialist care in hospital or a hospice, or you may be able to look after them at home with appropriate support.
