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Chromosome 20


Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 20, one copy inherited from each parent, form one of the pairs. Chromosome 20 spans about 63 million DNA building blocks (base pairs) and represents approximately 2 percent of the total DNA in cells.

Identifying the genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 20 likely contains 500 to 600 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.

Health Conditions Related to Chromosomal Changes

The following chromosomal conditions are associated with changes in the structure or number of copies of chromosome 20.

Alagille syndrome

Approximately 7 percent of individuals with Alagille syndrome have small deletions of genetic material on chromosome 20, in a region known as 20p12. This region includes the JAG1 gene, which is involved in signaling between neighboring cells during embryonic development. This signaling influences how the cells are used to build body structures in the developing embryo. Loss of the JAG1 gene probably disrupts the signaling pathway. As a result, errors may occur during development, and these errors can affect the heart, bile ducts in the liver, the spinal column, and certain facial features.

More About This Health Condition

Ring chromosome 20 syndrome

Ring chromosome 20 syndrome is caused by a chromosomal abnormality known as a ring chromosome 20 or r(20). A ring chromosome is a circular structure that occurs when a chromosome breaks in two places and its broken ends fuse together. People with ring chromosome 20 syndrome have one copy of this abnormal chromosome in some or all of their cells.

It is not well understood how the ring chromosome causes the signs and symptoms of this syndrome. In some affected individuals, genes near the ends of chromosome 20 are deleted when the ring chromosome forms. Researchers suspect that the loss of these genes may be responsible for epilepsy and other health problems. However, most affected individuals do not have these gene deletions. In these people, the ring chromosome may change the activity of certain genes on chromosome 20, or the chromosome may be unable to copy (replicate) itself normally during cell division. Researchers are still working to determine the precise relationship between the ring chromosome 20 and the characteristic features of the syndrome.

More About This Health Condition


Changes in chromosome 20 are associated with several types of cancer. These chromosome abnormalities are somatic, which means they are acquired during a person's lifetime and are present only in certain cells. Deletions involving the long (q) arm of chromosome 20 appear to be common in blood-related cancers such as leukemia and lymphoma. Deletions of this chromosomal region have also been associated with other disorders of the blood and bone marrow, including polycythemia vera (which causes an overproduction of red blood cells) and myelodysplastic syndrome (which leads to a shortage of healthy blood cells).

Researchers are working to determine which genes on chromosome 20 are disrupted in people with these conditions. Studies suggest that some genes on the long arm of the chromosome may play critical roles in controlling the growth and division of cells.

Other chromosomal conditions

Deletions or duplications of genetic material from chromosome 20 can have a variety of effects, including intellectual disabilities, delayed development, distinctive facial features, skeletal abnormalities, and heart defects. Several different changes in the structure of chromosome 20 have been reported. These include an extra segment of the short (p) or long (q) arm of the chromosome in each cell (partial trisomy 20p or 20q) or a missing segment of the short or long arm of the chromosome in each cell (partial monosomy 20p or 20q).

Additional Information & Resources

Scientific Articles on PubMed


  • Alpman A, Serdaroglu G, Cogulu O, Tekgul H, Gokben S, Ozkinay F. Ring chromosome 20 syndrome with intractable epilepsy. Dev Med Child Neurol. 2005 May;47(5):343-6. doi: 10.1017/s0012162205000642. Citation on PubMed
  • Bench AJ, Nacheva EP, Hood TL, Holden JL, French L, Swanton S, Champion KM, Li J, Whittaker P, Stavrides G, Hunt AR, Huntly BJ, Campbell LJ, Bentley DR, Deloukas P, Green AR. Chromosome 20 deletions in myeloid malignancies: reduction of the common deleted region, generation of a PAC/BAC contig and identification of candidate genes. UK Cancer Cytogenetics Group (UKCCG). Oncogene. 2000 Aug 10;19(34):3902-13. doi: 10.1038/sj.onc.1203728. Citation on PubMed
  • Blanc P, Gouas L, Francannet C, Giollant M, Vago P, Goumy C. Trisomy 20q caused by interstitial duplication 20q13.2: clinical report and literature review. Am J Med Genet A. 2008 May 15;146A(10):1307-11. doi: 10.1002/ajmg.a.32278. Citation on PubMed
  • Canevini MP, Sgro V, Zuffardi O, Canger R, Carrozzo R, Rossi E, Ledbetter D, Minicucci F, Vignoli A, Piazzini A, Guidolin L, Saltarelli A, dalla Bernardina B. Chromosome 20 ring: a chromosomal disorder associated with a particular electroclinical pattern. Epilepsia. 1998 Sep;39(9):942-51. doi: 10.1111/j.1528-1157.1998.tb01443.x. Citation on PubMed
  • Chaabouni M, Turleau C, Karboul L, Jemaa LB, Maazoul F, Attie-Bitach T, Romana S, Chaabouni H. De novo trisomy 20p of paternal origin. Am J Med Genet A. 2007 May 15;143A(10):1100-3. doi: 10.1002/ajmg.a.31704. Citation on PubMed
  • Deloukas P, Matthews LH, Ashurst J, Burton J, Gilbert JG, Jones M, Stavrides G, Almeida JP, Babbage AK, Bagguley CL, Bailey J, Barlow KF, Bates KN, Beard LM, Beare DM, Beasley OP, Bird CP, Blakey SE, Bridgeman AM, Brown AJ, Buck D, Burrill W, Butler AP, Carder C, Carter NP, Chapman JC, Clamp M, Clark G, Clark LN, Clark SY, Clee CM, Clegg S, Cobley VE, Collier RE, Connor R, Corby NR, Coulson A, Coville GJ, Deadman R, Dhami P, Dunn M, Ellington AG, Frankland JA, Fraser A, French L, Garner P, Grafham DV, Griffiths C, Griffiths MN, Gwilliam R, Hall RE, Hammond S, Harley JL, Heath PD, Ho S, Holden JL, Howden PJ, Huckle E, Hunt AR, Hunt SE, Jekosch K, Johnson CM, Johnson D, Kay MP, Kimberley AM, King A, Knights A, Laird GK, Lawlor S, Lehvaslaiho MH, Leversha M, Lloyd C, Lloyd DM, Lovell JD, Marsh VL, Martin SL, McConnachie LJ, McLay K, McMurray AA, Milne S, Mistry D, Moore MJ, Mullikin JC, Nickerson T, Oliver K, Parker A, Patel R, Pearce TA, Peck AI, Phillimore BJ, Prathalingam SR, Plumb RW, Ramsay H, Rice CM, Ross MT, Scott CE, Sehra HK, Shownkeen R, Sims S, Skuce CD, Smith ML, Soderlund C, Steward CA, Sulston JE, Swann M, Sycamore N, Taylor R, Tee L, Thomas DW, Thorpe A, Tracey A, Tromans AC, Vaudin M, Wall M, Wallis JM, Whitehead SL, Whittaker P, Willey DL, Williams L, Williams SA, Wilming L, Wray PW, Hubbard T, Durbin RM, Bentley DR, Beck S, Rogers J. The DNA sequence and comparative analysis of human chromosome 20. Nature. 2001 Dec 20-27;414(6866):865-71. doi: 10.1038/414865a. Citation on PubMed
  • Ensembl Human Map View
  • Galanopoulos AG, Symeonidis A, Kourakli A, Papadaki EA, Tsaftaridis P, Terpos E, Aktipi A, Roussou P, Protopappa M, Pappaioannou M, Zikos P, Speletas M, Parcharidou A, Laoutaris N, Anagnostopoulos NI, Meletis J, Pangalis GA, Zoumbos N, Viniou N; Hellenic MDS Study Group. Prognostic significance of deletion of the long arm of chromosome 20 in patients with myelodysplastic syndrome (MDS): a study of the Greek MDS Study Group. Eur J Haematol. 2007 Jan;78(1):89-90. doi: 10.1111/j.1600-0609.2006.00764.x. No abstract available. Citation on PubMed
  • Gilbert F. Disease genes and chromosomes: disease maps of the human genome. Genet Test. 1997-1998;1(3):225-9. doi: 10.1089/gte.1997.1.225. No abstract available. Citation on PubMed
  • Grange DK, Garcia-Heras J, Kilani RA, Lamp S. Trisomy 20q13 --> 20qter in a girl with multiple congenital malformations and a recombinant chromosome 20 inherited from a paternal inversion (20)(p13q13.1): clinical report and review of the trisomy 20q phenotype. Am J Med Genet A. 2005 Sep 1;137A(3):308-12. doi: 10.1002/ajmg.a.30877. Citation on PubMed
  • Inoue Y, Fujiwara T, Matsuda K, Kubota H, Tanaka M, Yagi K, Yamamori K, Takahashi Y. Ring chromosome 20 and nonconvulsive status epilepticus. A new epileptic syndrome. Brain. 1997 Jun;120 ( Pt 6):939-53. doi: 10.1093/brain/120.6.939. Citation on PubMed
  • Kamath BM, Thiel BD, Gai X, Conlin LK, Munoz PS, Glessner J, Clark D, Warthen DM, Shaikh TH, Mihci E, Piccoli DA, Grant SF, Hakonarson H, Krantz ID, Spinner NB. SNP array mapping of chromosome 20p deletions: genotypes, phenotypes, and copy number variation. Hum Mutat. 2009 Mar;30(3):371-8. doi: 10.1002/humu.20863. Citation on PubMed or Free article on PubMed Central
  • Nishiwaki T, Hirano M, Kumazawa M, Ueno S. Mosaicism and phenotype in ring chromosome 20 syndrome. Acta Neurol Scand. 2005 Mar;111(3):205-8. doi: 10.1111/j.1600-0404.2005.00298.x. Citation on PubMed
  • Oppenheimer S, Dignan P, Soukup S. Partial trisomy 20p: familial occurrence. Am J Med Genet. 2000 Dec 11;95(4):316-9. Citation on PubMed
  • UCSC Genome Browser: Statistics

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.