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Chromosome 20 trisomy

Other Names for this Disease
  • Mosaic trisomy 20
  • Trisomy 20
  • Trisomy 20 mosaicism
  • Trisomy chromosome 20
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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: 12/17/2010


  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. Accessed 12/17/2010.
  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. Accessed 12/17/2010.
  3. Chromosome abnormalities. March of Dimes. December 2009; Accessed 12/17/2010.
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