MedlinePlus Medical Encyclopedia: Trisomy 18

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Trisomy 18

Contents of this page:
Illustrations Alternative names Definition Causes, incidence, and risk factors Symptoms Signs and tests	Treatment Support Groups Expectations (prognosis) Complications Calling your health care provider Prevention

Illustrations

Syndactyly

Alternative names Return to top

Edwards syndrome

Definition Return to top

Trisomy 18 is a syndrome associated with the presence of a third (extra) number 18 chromosome.

Causes, incidence, and risk factors Return to top

Trisomy 18 is a relatively common syndrome affecting approximately 1 out of 3,000 live births and affecting girls more than three times as often as boys. Multiple abnormalities are associated with the presence of an extra number 18 chromosome. Many of these abnormalities are not compatible with more than a few months of life. Few infants survive beyond the first year.

Common findings include low birth weight, mental retardation, low-set ears, malformed ears, small jaw (micrognathia), hand abnormalities, congenital heart disease, hernias, and undescended testicle (cryptorchidism). There may be many other abnormalities noted.

Symptoms Return to top

Unusually large uterus during pregnancy
Low birth weight infant
Mental deficiency
Low-set ears
Small jaw (micrognathia)
Clenched hands
Hypoplastic (underdeveloped) fingernails
Umbilical hernia or inguinal hernia
Diastasis recti
Cryptorchidism
Crossed legs (preferred position)
Congenital heart disease
- VSD (ventricular septal defect)
- ASD (atrial septal defect)
- PDA (patent ductus arteriosus)
Congenital kidney abnormalities
- Horseshoe kidney
- Hydronephrosis
- Polycystic kidney
Coloboma of iris
Microcephaly
Motormental retardation
Pectus carinatum

Signs and tests Return to top

Examination of the pregnant woman may show polyhydramnios (extra amniotic fluid). At the birth of the child, an unusually small placenta may be noted.

Physical examination may show an excess of arched type finger print patterns. X-rays may reveal a short breast bone (sternum). Chromosome studies show trisomy 18, partial trisomy, or translocation.

Treatment Return to top

Treatment is supportive, but life-sustaining measures are not recommended.

Support Groups Return to top

Support Organization for Trisomy 18, 13 and Related Disorders (SOFT)
2982 S Union St
Rochester, NY 14624
716-594-4621
800-716-7638
www.trisomy.org

Trisomy 18 Support Foundation, Inc.
4301 Connecticut Ave. N.W. Suite 404
Washington, D.C. 20008-2369
757-464-5905
www.trisomy18support.org

Expectations (prognosis) Return to top

The abnormalities of trisomy 18 are generally not compatible with more than a few months of life. Fifty percent of the affected infants do not survive beyond the first week of life. More than 10 children have survived to teenage years, but usually with marked handicaps.

Complications Return to top

Complications depend on the specific abnormalities that affect the infant.

Calling your health care provider Return to top

Call your health care provider and genetic counselor if you have had a child with Trisomy 18 and you plan to have another child.

Prevention Return to top

Prenatal diagnosis of trisomy 18 is possible with an amniocentesis and chromosome studies on amniotic cells. Parents who have a child with translocational trisomy 18 should have chromosome studies, because they are at increased risk for another child with trisomy 18.

Update Date: 8/19/2003

Updated by: Douglas R. Stewart, M.D., Division of Medical Genetics, Hospital of the University of Pennsylvania, Philadelphia, PA. Review provided by VeriMed Healthcare Network.

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