National Center for Advancing and Translational Sciences Genetic and Rare Diseases Information Center, a program of the National Center for Advancing and Translational Sciences

Chromosome 20 trisomy

Información en español


Other Names:
Trisomy chromosome 20; Trisomy 20; Trisomy 20 mosaicism; Trisomy chromosome 20; Trisomy 20; Trisomy 20 mosaicism; Mosaic trisomy 20 See More
Categories:
Chromosome 20 trisomy, (also called trisomy 20) is a condition in which a fetus or individual has an extra full or partial copy of chromosome 20 in some or all of of his/her cells. An extra full copy of chromosome 20 in all of a person's cells is rare, and almost all fetuses with this do not survive past the first trimester of pregnancy.[1] The presence of an extra copy of only part of chromosome 20 is called partial trisomy 20; and an extra copy of chromosome 20 in only some of a person's cells is called mosaic trisomy 20. Mosaic trisomy 20 is the most common type of chromosome 20 trisomy and is one of the more common chromosomal abnormalities found during prenatal diagnostic testing. Studies have shown that the child is normal in the vast majority of prenatally diagnosed individuals. However, features that have been reported include spinal abnormalities (including spinal stenosis, vertebral fusion, and kyphosis), hypotonia (decreased muscle tone), lifelong constipation, sloped shoulders, and significant learning disabilities despite normal intelligence.[2] Trisomy 20 usually results from an error that occurs when an egg or sperm cell develops (before fertilization); mosaic trisomy 20 usually results from errors in cell division soon after fertilization.[3]
Last updated: 10/7/2016
Chromosomal abnormalities usually result from an error that occurs when an egg or sperm cell develops. It is not always known why these errors occur, but it is thought that nothing that a parent does or doesn’t do before or during pregnancy can cause a chromosomal abnormality in a fetus or child. Egg and sperm cells should each contain 23 chromosomes. When they join together, they form a fertilized egg with 46 chromosomes. Sometimes, something goes wrong before fertilization. An egg or sperm cell may divide incorrectly, resulting in an egg or sperm cell with too many or too few chromosomes. When this cell with the wrong number of chromosomes joins with a normal egg or sperm cell, the resulting embryo has a chromosomal abnormality. If an egg or sperm cell has 24 chromosomes because either has an extra copy of chromosome 20, this can cause trisomy 20 (the resulting embryo will have 3 copies of chromsome 20). In most cases, an embryo with 3 full copies of chromosome 20 in all cells does not survive and the pregnant woman has a miscarriage, often very early in pregnancy.

Other types of errors can alter the structure of one or more chromosomes. Individuals with structural chromosomal abnormalities usually have the normal number of chromosomes. However, small pieces of a chromosome (or chromosomes) may be duplicated, and in the case of part of chromosome 20 being duplicated, it would be called partial trisomy 20 (because there are 3 copies of only part of chromosome 20 in each cell).

Errors in cell division involving chromosome 20 can also occur soon after fertilization, which can cause mosaicism, a condition in which an individual has cells with different genetic makeups. Individuals with the mosaic form of trisomy 20 have an extra chromosome 20 in some, but not all, of their cells. Some individuals with chromosomal mosaicism may be mildly affected or apparently not affected at all, but the severity of the condition may depend on the number of abnormal cells that are present. Other individuals may be severely affected.[3]
Last updated: 10/7/2016
Most cases of chromosome 20 trisomy are not inherited and result from random events during the formation of eggs and sperm in healthy parents. An error in cell division, called nondisjunction, results in an egg or sperm cell with an abnormal number of chromosomes. If an egg or sperm cell gains an extra copy of chromosome 20, the embryo will have an extra chromosome 20 in each cell of the body. For more information about the causes of different types of chromosome 20 trisomy (full, partial or mosaic trisomy 20) click here.

Translocation trisomy 20 can be inherited. A  healthy person (that does not have trisomy 20) can carry a rearrangement of genetic material between chromosome 20 and another chromosome (called a translocation). These rearrangements are called balanced translocations because there is no extra material from chromosome 20. A person with a balanced translocation involving chromosome 20 has an increased chance of passing extra material from chromosome 20 to his/her child, which would result in a form of trisomy 20 in the child.[4]
Last updated: 10/7/2016

Research helps us better understand diseases and can lead to advances in diagnosis and treatment. This section provides resources to help you learn about medical research and ways to get involved.

Patient Registry

  • The Tracking Rare Incidence Syndromes (TRIS) project seeks to increase the knowledge base on rare incidence trisomy conditions, and to make this information available to families and interested educational, medical and therapeutic professionals.

    TRIS Project
    Deborah A. Bruns, Ph.D., Principal Investigator
    Counseling, Quantitative Methods, and Special Education
    Wham Building, Room 223 MC 4618
    Carbondale, IL 62901
    Phone: 618-453-2311
    E-mail: tris@siu.edu

Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Organizations Supporting this Disease

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

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.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Chromosome 20 trisomy. Click on the link to view a sample search on this topic.

Questions sent to GARD may be posted here if the information could be helpful to others. We remove all identifying information when posting a question to protect your privacy. If you do not want your question posted, please let us know. Submit a new question

  • What can happen if you have mosaic trisomy 20? See answer

  • Can a person with chromosome 20 trisomy pass this on to his/her children? See answer


  1. Mavromatidis G, Dinas K, Delkos D, Vosnakis C, Mamopoulos A, Rousso D. Case of prenatally diagnosed non-mosaic trisomy 20 with minor abnormalities. Journal of Obstetrics and Gynaecology Reearch. August 2010; 36(4):866-868. http://www.ncbi.nlm.nih.gov/pubmed/20666959.
  2. Willis MJ, Bird LM, Dell'Aquilla M, Jones MC. Expanding the phenotype of mosaic trisomy 20. American Journal of Medical Genetics. February 1, 2008; 146(3):330-336. http://www.ncbi.nlm.nih.gov/pubmed/18203170.
  3. Chromosome abnormalities. March of Dimes. February 2013; http://www.marchofdimes.com/Baby/birthdefects_chromosomal.html.
  4. Trisomy 13. Genetics Home Reference. November 2013; http://ghr.nlm.nih.gov/condition/trisomy-13. Accessed 11/27/2015.