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Diseases

Genetic and Rare Diseases Information Center (GARD)

Trisomy 18


Other Names for this Disease
  • 18 trisomy
  • Chromosome 18 duplication
  • Chromosome 18 trisomy
  • Edwards syndrome
  • Trisomy 16-18 (formerly)
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.

Your Question

I lost a baby to Edwards syndrome. Are my surviving children at risk for any problems as a result?

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

What is Trisomy 18?

Trisomy 18 is a chromosome disorder characterized by having 3 copies of chromosome 18 instead of the usual 2 copies. Signs and symptoms include severe intellectual disability; low birth weight; a small, abnormally shaped head; a small jaw and mouth; clenched fists with overlapping fingers; congenital heart defects; and various abnormalities of other organs. Trisomy 18 is a life-threatening condition; many affected people die before birth or within the first month of life. Some children have survived to their teenage years, but with serious medical and developmental problems. Most cases are not inherited and occur sporadically (by chance).[1][2]
Last updated: 7/7/2015

What causes Trisomy 18?

In most cases, trisomy 18 is caused by having 3 copies of chromosome 18 in each cell in the body, instead of the usual 2 copies. The extra genetic material from the 3rd copy of the chromosome disrupts development, causing the characteristic signs and symptoms of the condition.

About 5% of people with trisomy 18 have 'mosaic trisomy 18' (when there is an extra copy of the chromosome in only some of the body's cells). The severity of mosaic trisomy 18 depends on the number and locations of cells with the extra copy.

Very rarely, an extra piece of chromosome 18 is attached to another chromosome; this is called translocation trisomy 18, or partial trisomy 18. If only part of the long (q) arm of chromosome 18 is present in 3 copies, the features may be less severe than in people with full trisomy 18.[1]
Last updated: 1/30/2012

Is trisomy 18 inherited?

Most cases of trisomy 18 are not inherited and occur randomly due to errors in the formation of eggs or sperm. If an egg or sperm gains an extra copy of chromosome 18 during cell division and contributes to a pregnancy, the embryo will have an extra chromosome 18 (trisomy) in each cell of the body.

Mosaic trisomy 18 (when some body cells have trisomy 18 and some have a normal chromosome make-up), is also typically not inherited. Mosaic trisomy 18 is also due to an error in cell division, but the error occurs early in embryonic development. About 5% of affected people have a mosaic form of trisomy 18.

Partial trisomy 18 (when only part of chromosome 18 is present in 3 copies) can be inherited. An unaffected parent 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 or missing genetic material. However, a person with a balanced translocation has an increased risk with each pregnancy to have a child with trisomy 18.[1]
Last updated: 7/7/2015

Are my children at risk for any problems as a result of our family history of Trisomy 18?

Most cases of trisomy 18 occur as random events during the formation of reproductive cells (eggs and sperm).[3] The risk of recurrence of trisomy (21, 13 or 18) in families of an individual with trisomy 18 is around 1%. However, in families in which trisomy 18 is caused by a translocation, the recurrence risk is higher if one of the parents is a carrier of a balanced translocation.[4] Parents who have a child with translocational trisomy 18 and want additional children are encouraged to have chromosome studies due to this increased risk.[2] The risk to siblings of individuals with trisomy 18 depends, in large part, on the genetic status of the parents, as translocation cases can be passed through families with carriers being asymptomatic. Genetic studies (chromosome analysis) can determine if translocations are present. 

We recommend that you discuss this information and your concerns with a genetics professional. The following online resources can help you find a genetics professional in your community:

 * GeneClinics - A searchable directory of US and international genetics and prenatal diagnosis clinics. To locate genetics clinics in the United States, go to the following link and click on 'Clinic Directory' to find a genetic service close to you. 

  * ResourceLink - A database of genetics counseling services, searchable by location, name, institution, type of practice, or specialty. Hosted by the National Society of Genetic Counselors.

Last updated: 1/30/2012

References
Other Names for this Disease
  • 18 trisomy
  • Chromosome 18 duplication
  • Chromosome 18 trisomy
  • Edwards syndrome
  • Trisomy 16-18 (formerly)
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.