Edwards Syndrome (Trisomy 18)

What Edwards syndrome is

Each cell normally has 23 pairs of chromosomes. In trisomy 18 there are three copies of chromosome 18. The extra genetic material disrupts development of many organs before birth. It is the second most common autosomal trisomy at birth, after Down syndrome (trisomy 21), and is more common than Patau syndrome (trisomy 13).

More girls than boys are born with it, because male fetuses with trisomy 18 are more likely to be lost during pregnancy.

Types of trisomy 18

Symptoms and features

Signs often show up on pregnancy ultrasound:

• slow growth of the baby (intrauterine growth restriction)
• too much amniotic fluid (polyhydramnios)
• a small placenta and a single umbilical artery
• clenched hands, heart defects, choroid plexus cysts in the brain, or a strawberry-shaped skull

At birth, babies typically have:

• Low birth weight and weak cry
• Clenched fists with the index finger overlapping the middle finger and the little finger over the ring finger
• Rocker-bottom feet with a rounded sole
• Small jaw and mouth (micrognathia), low-set, unusually shaped ears, and a prominent back of the head
• Short breastbone and small pelvis
• Heart defects in about 90 in 100, most commonly holes between chambers (VSD, ASD) and a persistent ductus arteriosus. See congenital heart defects.
• Other organ differences: an omphalocele (bowel outside the belly wall), kidney malformations, esophageal atresia, cleft lip or palate, eye abnormalities
• Feeding and breathing problems, including weak sucking and pauses in breathing (apnea)

Children who survive infancy have severe intellectual disability and developmental delay. Many learn to smile, recognize family, and respond to their surroundings. Some learn to sit with support or use simple communication. Mosaic forms can have much milder effects.

Causes

In most cases, the extra chromosome comes from an error in cell division (nondisjunction) when the egg or, less often, the sperm forms. This happens by chance. The parents did nothing to cause it.

• The chance rises with the mother's age, as with other trisomies.
• Mosaic trisomy 18 comes from an error after conception, so only some cells are affected.
• Partial trisomy 18 can occur when a parent carries a balanced translocation, a harmless rearrangement of their own chromosomes. In this situation, the recurrence risk is higher, so parents' chromosomes are tested.

For full trisomy 18, the chance of it happening again in a later pregnancy is low, often quoted as about 1 in 100.

Diagnosis

During pregnancy

• Screening: cell-free DNA testing (NIPT) of the mother's blood from 10 weeks is the most accurate screening test. The first-trimester combined test and the second-trimester quad screen also estimate the chance.
• Ultrasound: the detailed anatomy scan at 18 to 22 weeks often shows features of trisomy 18.
• Diagnostic tests: chorionic villus sampling (CVS) at 10 to 13 weeks or amniocentesis from 15 weeks confirm the diagnosis by testing fetal cells. Screening alone cannot confirm it.

After birth

A blood test for chromosome analysis (karyotype) confirms the diagnosis, usually within days. A rapid test (FISH) can give a preliminary result within 1 to 2 days. Babies then have an echocardiogram, abdominal ultrasound and other checks to find associated problems.

Treatment and care

There is no cure. Care is planned around each baby's needs and the family's values, with a team that often includes neonatologists, cardiologists, geneticists, palliative care and social workers.

Care options

• Comfort-focused (palliative) care: keeping the baby warm, fed and comfortable, and supporting time together as a family.
• Medical support: feeding by tube, oxygen or breathing support, medicines for heart failure and reflux, and treatment of infections.
• Surgery: some centers offer heart surgery or other operations. Studies show that selected children who have heart surgery live longer, though they still have significant disability. Decisions are made case by case.

Ongoing needs for children who survive

• Feeding support, often a gastrostomy tube
• Physical, occupational and speech therapy
• Monitoring for scoliosis, hearing and vision problems, and certain childhood kidney and liver tumors (ultrasound screening is often advised)
• Respite care and family support

Outlook and life expectancy

Trisomy 18 has a serious outlook:

• Many affected pregnancies end in miscarriage or stillbirth.
• Of babies born alive, about half live longer than 1 to 2 weeks.
• About 5 to 10 in 100 live past their first birthday, and a small number reach their teens or adulthood.
• Survival is longer with mosaic and partial forms, in girls, and in babies who receive active treatment including heart surgery.

The main causes of death are heart failure, breathing problems such as central apnea, and infections.

Genetic counseling helps families understand the diagnosis, test results, recurrence risks and options in future pregnancies. Parent support groups such as SOFT connect families facing the same diagnosis.

Frequently asked questions

What are the symptoms of Edwards syndrome?

Babies with Edwards syndrome typically have low birth weight, clenched hands with overlapping fingers, rocker-bottom feet, a small jaw, heart defects, feeding and breathing difficulties, and severe developmental delay. Many features are seen on pregnancy ultrasound before birth.

What is the life expectancy of a baby with trisomy 18?

Many babies with full trisomy 18 live only days to weeks. About half survive beyond the first week or two, and about 5 to 10 in 100 live past their first birthday. Some with mosaic or partial trisomy 18, or who receive active treatment, live much longer.

Is trisomy 18 inherited?

Usually not. Most cases result from a random error in egg or sperm formation. Rarely, a parent carries a balanced chromosome rearrangement that raises the risk, which is why parents may be offered a chromosome test after a diagnosis.

Can trisomy 18 be detected before birth?

Yes. Cell-free DNA screening and ultrasound can show a high chance of trisomy 18 during pregnancy. A diagnostic test, CVS or amniocentesis, confirms it. Many cases are found at the 18 to 22 week anatomy scan.

What is the difference between Edwards syndrome and Down syndrome?

Both are trisomies. Down syndrome is an extra chromosome 21, causes milder physical effects, and most people live into adulthood. Edwards syndrome is an extra chromosome 18, causes more severe organ problems, and most babies have a short life.