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Genetic and Rare Diseases Information Center (GARD)

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Trisomy 17 mosaicism

Other Names for this Disease
  • Chromosome 17 duplication
  • Chromosome 17 trisomy
  • Chromosome 17, trisomy
  • Chromosome 17, trisomy mosaicism
  • Trisomy 17
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Your Question

My wife and I had a child born with trisomy 17 mosaicism. Since then, we have had two healthy children. What is known about this chromosomal abnormality? I can't seem to find any information that is easy to read or find. When our child was born about 20 years ago, we where told that there had only been 7 live births and none had lived past 4 years of age.

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 17 mosaicism?

Trisomy 17 mosaicism is a chromosomal abnormality in which there are three copies of chromosome 17 in some cells of the body, rather than the usual two copies. Trisomy 17 mosaicism is one of the rarest trisomies in humans. It is often incorrectly called trisomy 17 (also referred to as full trisomy 17), which is when three copies of chromosome 17 are present in all cells of the body. Full trisomy 17 has never been reported in a living individual in the medical literature.[1] Few cases of trisomy 17 mosaicism have been described, most having been detected during pregnancy through a test called amniocentesis.[2] Only a few individuals have had a confirmed diagnosis of trisomy 17 mosaicism after birth. Because the proportion and location of cells with trisomy 17 differs from case to case, the presence and severity of signs and symptoms may vary significantly from person to person.
Last updated: 5/8/2013

What signs and symptoms have been observed in individuals diagnosed with trisomy 17 mosaicism?

A review of the medical literature shows that most cases of trisomy 17 mosaicism detected during pregnancy via chorionic villus sampling (CVS) or amniocentesis are not confirmed in the baby after birth; those babies appeared to be in good health at birth. Seven cases of trisomy 17 mosaicism detected during pregnancy have been confirmed in the baby after birth and the clinical symptoms for those children have included developmental delays, body asymmetry, slow growth, and cerebellar hypoplasia. Again, signs and symptoms may vary in these patients depending on which cells and how many cells contain an extra chromosome 17.[1179]
Last updated: 5/21/2009

What causes trisomy 17 mosaicism?

Trisomy 17 mosaicism can arise due to errors in cell division that occur after conception. For example, at the time of conception, the fetus may actually have trisomy 17 in all of its cells; however, during cell division, some of the cells lose the extra chromosome 17. Alternatively, the fetus may initially have had only two copies of chromosome 17, but due to errors in cell division some of the cells end up with an extra copy of chromosome 17. Either of these two scenarios result in trisomy 17 mosaicism.

To read more about trisomy mosaicism, visit the following links from the Medical Genetics Department at the University of British Columbia in Canada.

Last updated: 5/21/2009

How can I locate additional cases of trisomy 17 mosaicism that have been documented in the medical literature?

You can find relevant journal articles on trisomy 17 mosaicism through a service called PubMed, a searchable database of medical literature. Information on finding an article and its title, authors, and publishing details is listed here.  Some articles are available as a complete document, while information on other studies is available as a summary abstract.  To obtain the full article, contact a medical/university library (or your local library for interlibrary loan), or order it online using the following link. Using "trisomy 17 mosaicism[ti]" as your search term should locate articles. To narrow your search, click on the “Limits” tab under the search box and specify your criteria for locating more relevant articles.  Click here to view a search.

The National Library of Medicine (NLM) Web site has a page for locating libraries in your area that can provide direct access to these journals (print or online). The Web page also describes how you can get these articles through interlibrary loan and Loansome Doc (an NLM document-ordering service). You can access this page at the following link You can also contact the NLM toll-free at 888-346-3656 to locate libraries in your area.

Last updated: 5/21/2009

How might be able to locate additional information as well as support resources for trisomy 17 mosaicism?

Click here to view resources related to trisomy 17 mosaicism.
Last updated: 5/21/2009

  • Hassold T. Mosaic trisomies in human spontaneous abortions. Hum Genet. 1982;
  • Utermann B, Riegel M, Leistritz D, Karall T, Wisser J, Meisner L et al. Pre- and Postnatal Findings in Trisomy 17 Mosaicism. Am J Med Genet Part A. 2006;