The following information may help to address your question:
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.
Few cases of trisomy 17 mosaicism have been described, most having been detected during pregnancy through a test called amniocentesis
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 are the signs and symptoms of trisomy 17 mosaicism?
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)
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.
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.
Last updated: 8/30/2016
What causes trisomy 17 mosaicism?
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
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" 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 http://nnlm.gov/members/. You can also contact the NLM toll-free at 888-346-3656 to locate libraries in your area.
Last updated: 8/29/2016
What organizations support trisomy 17 mosaicism?
Last updated: 8/29/2016
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