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Trisomy 17 mosaicism


Other Names:
Chromosome 17 duplication; Trisomy 17; Chromosome 17 trisomy; Chromosome 17 duplication; Trisomy 17; Chromosome 17 trisomy; Chromosome 17, trisomy; Chromosome 17, trisomy mosaicism See More
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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
While trisomy 17 mosaicism is rare, there are a few cases that have been reported in the medical literature as well as a few reviews. Most cases of trisomy 17 mosaicism reported in the medical literature that were detected during pregnancy via chorionic villus sampling (CVS) or amniocentesis have not been confirmed in the baby after birth. In those cases, the babies appeared to be in good health at birth and it is suspected that in those cases, trisomy 17 was confined to extra-embryonic (placental) cells and tissues.[3][4]

Some cases of trisomy 17 mosaicism detected during pregnancy have been confirmed in the baby after birth. The symptoms reported include: developmental delays, body asymmetry, slow growth, and cerebellar hypoplasia. Again, signs and symptoms may vary in these individuals depending on which cells and how many cells contain an extra chromosome 17.[3][4]
Last updated: 8/30/2016
Trisomy 17 mosaicism occurs due to a random event during the formation of the reproductive cells (egg and sperm) or after fertilization has taken place. An error in cell division (called nondisjunction) may cause some eggs or sperm to have an abnormal number of chromosomes. If an egg or sperm with an extra chromosome 17 contributes to the genetic makeup of an embryo, the embryo will have an extra copy of chromosome 17 in each cell. As the embryo grows and divides, an attempt may be made to correct the mistake by eliminating one extra chromosome 17. In individuals with trisomy 17 mosaicism, this attempt may be partly successful, leaving some cells with an extra chromosome 17 and some cells with the extra chromosome deleted (the usual chromosome number). This correction process is called trisomy rescue.

In other cases, the egg and sperm may have a normal number of chromosomes, but an error of cell division (nondisjunction) occurs when the fertilized egg is growing and dividing. If an error occurs during one of the divisions, it can cause some cells to have an abnormal number of chromosomes. In people affected by trisomy 17 mosaicism, some of the body's cells have the usual two copies of chromosome 17, and other cells have three copies of this chromosome (trisomy). The percentage of cells with trisomy 17 and which parts of the body are affected vary from person to person. This leads to variability in the range and severity of symptoms.

MedlinePlus, a resource through the National Library of Medicine, offers general information on mosaicism.

Last updated: 8/30/2016

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These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

Where to Start

  • The National Human Genome Research Institute, part of the National Institutes of Health (NIH), has developed a fact sheet on chromosome abnormalities, which may be helpful to you. To read this information, visit the link.

    MedlinePlus, the National Library of Medicine Web site designed to direct you to information and resources that help you research your health questions, provides further information about chromosomes. Click on the link.

In-Depth Information

  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Trisomy 17 mosaicism. Click on the link to view a sample search on this topic.

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  • 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. See answer


  1. Hassold T. Mosaic trisomies in human spontaneous abortions. Hum Genet. 1982;
  2. 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;
  3. Robert D. Daber, Kimberly A. Chapman, Eduardo Ruchelli, Stefanie Kasperski, Surabhi Mulchandani, Brian D. Thiel, Hakon Hakonarson, Elaine H. Zackai, Laura K. Conlin, Nancy B. Spinner. Mosaic Trisomy 17: Variable Clinical and Cytogenetic Presentation. Am J Med Genet A. October 2011; 155A(10):2489-2495. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3197730/.
  4. Witters IW, Fryns J. Follow-up of a child with trisomy 17 mosaicism. Prenat Diagn. 2008;
  5. Robert L. Nussbaum, Roderick R. McInnes, Huntington F. Willard. Thompson & Thompson Genetics In Medicine. Philadelphia, PA: Saunders Elsevier; 2007; 7:75-95.