Edwards syndrome (patient information)

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Assistant Editor-in-Chief: Ethan Leeman

Overview

Edwards syndrome, also known as Trisomy 18 is a genetic disorder in which a person has a third copy of genetic material from chromosome 18, instead of the usual two copies. The condition is associated with severe intellectual disability and abnormalities in many parts of the body. Individuals with trisomy 18 often have a low birth weight; a small, abnormally shaped head; a small jaw and mouth; clenched fists with overlapping fingers; heart defects; and abnormalities of other organs. Due to the presence of several life-threatening medical problems, many infants with trisomy 18 die within their first month. Five percent to 10 percent of children with this condition live past their first year.

Trisomy 18 occurs in about 1 in 5,000 newborns. Approximately 80 percent of newborns affected by this disorder are female. Although women of all ages can have a child with trisomy 18, the chance of having a child with this condition increases as a woman gets older.

What are the symptoms of Edwards syndrome?

• Clenched hands
• Crossed legs (preferred position)
• Feet with a rounded bottom (rocker-bottom feet)
• Low birth weight
• Low-set ears
• Mental deficiency
• Small jaw (micrognathia)
• Underdeveloped fingernails
• Undescended testicle
• Unusual shaped chest (pectus carinatum)

Genetics and Inheritance

Most cases of trisomy 18 result from having three copies of chromosome 18 in each cell in the body instead of the usual two copies. The extra genetic material disrupts the normal course of development, causing the characteristic features of trisomy 18.

Approximately 5 percent of people with trisomy 18 have an extra copy of chromosome 18 in only some of the body's cells. In these people, the condition is called mosaic trisomy 18. The severity of mosaic trisomy 18 depends on the type and number of cells that have the extra chromosome. The development of individuals with this form of trisomy 18 may range from normal to severely affected.

Very rarely, the long (q) arm of chromosome 18 becomes attached (translocated) to another chromosome during the formation of reproductive cells (eggs and sperm) or very early in embryonic development. Affected people have two copies of chromosome 18, plus extra material from chromosome 18 attached to another chromosome. If only part of the q arm is present in three copies, the physical signs of translocation trisomy 18 may be different from those typically seen in trisomy 18. If the entire q arm is present in three copies, individuals may be as severely affected as if they had three full copies of chromosome 18.

Most cases of trisomy 18 are not inherited, but occur as random events during the formation of eggs and sperm. An error in cell division called nondisjunction results in a reproductive cell with an abnormal number of chromosomes. For example, an egg or sperm cell may gain an extra copy of chromosome 18. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have an extra chromosome 18 in each of the body's cells.

Mosaic trisomy 18 is also not inherited. It occurs as a random event during cell division early in embryonic development. As a result, some of the body's cells have the usual two copies of chromosome 18, and other cells have three copies of this chromosome.

Translocation trisomy 18 can be inherited. An unaffected person can carry a rearrangement of genetic material between chromosome 18 and another chromosome. This rearrangement is called a balanced translocation because there is no extra material from chromosome 18. Although they do not have signs of trisomy 18, people who carry this type of balanced translocation are at an increased risk of having children with the condition.

When to seek medical care?

Call your health care provider and genetic counselor if you have had a child with Trisomy 18 and you plan to have another child. Genetic counseling can help families understand the condition, the risks of inheriting it, and how to care for the patient.

Diagnosis

Examination of the pregnant woman may show an unusually large uterus and extra amniotic fluid. An unusually small placenta may be seen when the baby is born.

Physical examination of the infant may show unusual fingerprint patterns. X-rays may show a short breast bone. Chromosome studies show trisomy 18, partial trisomy, or translocation.

Other signs include:

• Hole, split, or cleft in the iris (coloboma)
• Separation between the left and right side of the rectus abdominis muscle (diastasis recti)
• Umbilical hernia or inguinal hernia

There are often signs of congenital heart disease, such as:

• Atrial septal defect (ASD)
• Patent ductus arteriosus (PDA)
• Ventricular septal defect (VSD)

Tests may also show kidney problems, including:

• Horseshoe kidney
• Hydronephrosis
• Polycystic kidney

Treatment options

Treatment of children with Trisomy 18 is planned on a case-by-case basis. Which treatments are used depends on the patient's individual condition.

Where to find medical care for Edwards syndrome?

Directions to Hospitals Treating Edwards syndrome

Prevention

Prenatal diagnosis of trisomy 18 is possible with an amniocentesis or chorionic villus sampling and chromosome studies on amniotic cells. Parents who have a child with translocational Trisomy 18 and want additional children should have chromosome studies, because they are at increased risk of having another child with Trisomy 18.

What to expect (Outlook/Prognosis)?

Fifty percent of infants with this condition do not survive beyond the first week of life. Some children have survived to the teenage years, but with serious medical and developmental problems.

Sources

• Wikipedia
• Medline
• Genetics Home Reference