Trisomy 18

Definition

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

Syndactyly

Alternative Names

Edwards syndrome

Causes, incidence, and risk factors

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. It is caused by the presence of an extra number 18 chromosome, which leads to multiple abnormalities. Many of these abnormalities make it hard for infants to live longer than a few months.

Symptoms

• 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
• Pectus carinatum

Signs and tests

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

Life-sustaining measures are not recommended.

Support Groups

Contact the following organizations for more information:

• Support Organization for Trisomy 18, 13 and Related Disorders (SOFT):
• Trisomy 18 Foundation:

Expectations (prognosis)

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

Complications depend on the specific abnormalities that affect the infant.

Calling your health care provider

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

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 and want additional children should have chromosome studies, because they are at increased risk to have another child with trisomy 18.

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Review Date:4/20/2005
Reviewed By: Neal Sondheimer, M.D., PhD., Division of Genetics and Metabolism, Children's Hospital of Philadelphia, Philadelphia, PA. Review provided by VeriMed Healthcare Network.