- 18 trisomy
- Chromosome 18 duplication
- Chromosome 18 trisomy
- Edwards syndrome
- Trisomy 16-18 (formerly)
Your QuestionI lost a baby to Edwards syndrome. Are my surviving children at risk for any problems as a result?
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Trisomy 18 is a chromosomal condition associated with severe intellectual disability and abnormalities in many parts of the body. Affected individuals 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, fifty percent of infants with this condition do not survive beyond the first week of life. Some children have survived to teenage years, but with serious medical and developmental problems. 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. Most causes are not inherited and occur by chance.
People with Trisomy 18 have additional DNA from chromosome 18 in some or all of their cells. The extra material disrupts the normal course of development, causing the characteristic features of Trisomy 18.
Trisomy 18 results when each cell in the body has three copies of chromosome 18 instead of the usual two copies. A small percentage of cases occur when only some of the body's cells have an extra copy of chromosome 18, resulting in a mixed population of cells with a differing number of chromosomes. Such cases are sometimes called mosaic trisomy 18.
Very rarely, a piece of chromosome 18 becomes attached to another chromosome (translocated) before or after conception. Affected people have two copies of chromosome 18, plus extra material from chromosome 18 attached to another chromosome. With a translocation, the person has a partial trisomy for chromosome 18 and often the physical signs of the syndrome differ from those typically seen in full Trisomy 18.
The risk of having a child with trisomy 18 increases as a woman gets older.
Most cases of Trisomy 18 are not inherited, but occur as random events during the formation of reproductive cells (eggs and sperm). An error in cell division called nondisjunction results in reproductive cells 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 cell of the body.
Mosaic trisomy 18 is also not inherited. It occurs as a random error during cell division early in fetal 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 the 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.
Most cases of trisomy 18 occur as random events during the formation of reproductive cells (eggs and sperm). 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. Parents who have a child with translocational trisomy 18 and want additional children are encouraged to have chromosome studies due to this increased risk. 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
* 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.
- Trisomy 18. Genetics Home Reference (GHR). January 2009; http://ghr.nlm.nih.gov/condition/trisomy-18. Accessed 1/17/2012.
- Haldeman-Englert C. Trisomy 18. MedlinePlus. August 2011; http://www.nlm.nih.gov/medlineplus/ency/article/001661.htm. Accessed 1/17/2012.
- A. Verloes . Trisomy 18. Orphanet. May 2008; http://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=EN&Expert=3380. Accessed 12/16/2008.