Chromosome 21 (human)

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Chromosome 21 (human)
Human male karyotpe high resolution - Chromosome 21 cropped.png
Pair of human chromosome 21 (after G-banding).
One is from mother, one is from father.
Human male karyotpe high resolution - Chromosome 21.png
Chromosome 21 pair in human male karyogram.
Length (bp) 48,129,895
Number of genes 477[1]
Type Autosome
Centromere position Acrocentric[3]
RefSeq NC_000021
GenBank CM000683
Map of Chromosome 21
Ideogram of human chromosome 21. Mbp means mega base pair. See locus for other notation.

Chromosome 21 is one of the 23 pairs of chromosomes in humans. Chromosome 21 is the smallest human autosome, with 48 million nucleotides (the building material of DNA) representing about 1.5 percent of the total DNA in cells. People without Down's syndrome have two copies of chromosome 21, while those with three copies of chromosome 21 have Down syndrome, also called "trisomy 21".

Researchers working on the Human Genome Project announced that they had determined the sequence of base pairs that make up this chromosome. Chromosome 21 was the second human chromosome to be fully sequenced, after chromosome 22.

Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to genome annotation their predictions of the number of genes on each chromosome varies. In January 2017, two estimates differed by 33%, with one estimate giving 477[1] genes, and the other estimate giving 635[2] genes.


The following are some of the genes located on chromosome 21:

  • APP: amyloid beta (A4) precursor protein (peptidase nexin-II, Alzheimer disease)[4]
  • C21orf55/DNAJC28: encoding protein DnaJ homolog subfamily C member 28
  • C21orf56: encoding protein Uncharacterized protein C21orf56
  • C21orf59: Chromosome 21 open reading frame 59
  • C21orf66: encoding protein GC-rich sequence DNA-binding factor homolog
  • CBS: cystathionine-beta-synthase
  • CLDN14: claudin 14
  • HLCS: holocarboxylase synthetase (biotin-(propionyl-Coenzyme A-carboxylase (ATP-hydrolysing)) ligase)
  • KCNE1: potassium voltage-gated channel, Isk-related family, member 1
  • KCNE2: potassium voltage-gated channel, Isk-related family, member 2
  • LAD: leukocyte adhesion deficiency (symbols are ITGB2, CD18, LCAMB)
  • SOD1: superoxide dismutase 1, soluble (amyotrophic lateral sclerosis 1 (adult))
  • TMPRSS3: transmembrane protease, serine 3
  • PCNT: centrosomal pericentrin
  • DSCR1: Down Syndrome critical region 1[5]
  • DYRK1A: dual specificity tyrosine-(Y)-phosphorylation regulated kinase 1A
  • RRP1B: ribosomal RNA processing 1 homolog B
  • S100B: calcium binding protein
  • TTC3: Tetratricopeptide Repeat Domain 3

Diseases and disorders[edit]

The following diseases are some of those related to genes on chromosome 21:

Chromosomal conditions[edit]

Translocation Down's syndrome affecting Chromosome 21

The following conditions are caused by changes in the structure or number of copies of chromosome 21:

  • Cancers: Rearrangements (translocations) of genetic material between chromosome 21 and other chromosomes have been associated with several types of cancer. For example, acute lymphoblastic leukemia (a type of blood cancer most often diagnosed in childhood) has been associated with a translocation between chromosomes 12 and 21. Another form of leukemia, acute myeloid leukemia, has been associated with a translocation between chromosomes 8 and 21.
  • In a small percentage of cases, Down syndrome is caused by a rearrangement of chromosomal material between chromosome 21 and another chromosome. As a result, a person has the usual two copies of chromosome 21, plus extra material from chromosome 21 attached to another chromosome. These cases are called translocation Down syndrome. Researchers believe that extra copies of genes on chromosome 21 disrupt the course of normal development, causing the characteristic features of Down syndrome and the increased risk of medical problems associated with this disorder.
  • Other changes in the number or structure of chromosome 21 can have a variety of effects, including intellectual disability, delayed development, and characteristic facial features. In some cases, the signs and symptoms are similar to those of Down syndrome. Changes to chromosome 21 include a missing segment of the chromosome in each cell (partial monosomy 21) and a circular structure called ring chromosome 21. A ring chromosome occurs when both ends of a broken chromosome are reunited.
  • Duplication in Amyloid precursor protein (APP) locus (duplicated segment varies in length but includes APP) on Chromosome 21 was found to cause early onset familial Alzheimer's disease in a French family set (Rovelet-Lecrux et al.) and a Dutch family set.[4] Compared to Alzheimer's caused by missense mutations in APP, the frequency of the Alzheimer's caused by APP duplications is significant. All patients that have an extra copy of APP gene due to the locus duplication show Alzheimer's with severe cerebral amyloid angiopathy.


  1. ^ a b "Map Viewer". National Center for Biotechnology Information. Retrieved November 17, 2013. 
  2. ^ a b "Vega Genome Browser 54: Homo sapiens - Chromosome summary - Chromosome 21: 1-48,119,895". Wellcome Trust Sanger Institute. Retrieved November 17, 2013. 
  3. ^ "Table 2.3: Human chromosome groups". Human Molecular Genetics (2nd ed.). Garland Science. 1999. 
  4. ^ a b c Sleegers K, Brouwers N, Gijselinck I, Theuns J, Goossens D, Wauters J, Del-Favero J, Cruts M, van Duijn CM, Van Broeckhoven C (2006). "APP duplication is sufficient to cause early onset Alzheimer's dementia with cerebral amyloid angiopathy". Brain. 129 (Pt 11): 2977–83. doi:10.1093/brain/awl203. PMID 16921174. 
  5. ^ Gardiner K, Davisson M (2000). "The sequence of human chromosome 21 and implications for research into Down syndrome". Genome Biol. 1 (2): REVIEWS0002. doi:10.1186/gb-2000-1-2-reviews0002. PMC 138845Freely accessible. PMID 11178230. 
  • Antonarakis SE, Lyle R, Dermitzakis ET, Reymond A, Deutsch S (2004). "Chromosome 21 and down syndrome: from genomics to pathophysiology". Nat Rev Genet. 5 (10): 725–38. doi:10.1038/nrg1448. PMID 15510164. 
  • Antonarakis SE, Lyle R, Deutsch S, Reymond A (2002). "Chromosome 21: a small land of fascinating disorders with unknown pathophysiology". Int J Dev Biol. 46 (1): 89–96. PMID 11902692. 
  • Antonarakis SE (2001). "Chromosome 21: from sequence to applications". Curr Opin Genet Dev. 11 (3): 241–6. doi:10.1016/S0959-437X(00)00185-4. PMID 11377958. 
  • Gilbert F (1997). "Disease genes and chromosomes: disease maps of the human genome. Chromosome 21". Genet Test. 1 (4): 301–6. doi:10.1089/gte.1997.1.301. PMID 10464663. 
  • Hattori M, Fujiyama A, Taylor TD, Watanabe H, Yada T, Park HS, Toyoda A, Ishii K, Totoki Y, Choi DK, Groner Y, Soeda E, Ohki M, Takagi T, Sakaki Y, Taudien S, Blechschmidt K, Polley A, Menzel U, Delabar J, Kumpf K, Lehmann R, Patterson D, Reichwald K, Rump A, Schillhabel M, Schudy A, Zimmermann W, Rosenthal A, Kudoh J, Schibuya K, Kawasaki K, Asakawa S, Shintani A, Sasaki T, Nagamine K, Mitsuyama S, Antonarakis SE, Minoshima S, Shimizu N, Nordsiek G, Hornischer K, Brant P, Scharfe M, Schon O, Desario A, Reichelt J, Kauer G, Blocker H, Ramser J, Beck A, Klages S, Hennig S, Riesselmann L, Dagand E, Haaf T, Wehrmeyer S, Borzym K, Gardiner K, Nizetic D, Francis F, Lehrach H, Reinhardt R, Yaspo ML (2000). "The DNA sequence of human chromosome 21". Nature. 405 (6784): 311–9. doi:10.1038/35012518. PMID 10830953. 
  • Sawinska M, Ladon D (2004). "Mechanism, detection and clinical significance of the reciprocal translocation t(12;21)(p12;q22) in the children suffering from acute lymphoblastic leukaemia". Leuk Res. 28 (1): 35–42. doi:10.1016/S0145-2126(03)00160-7. PMID 14630078. 
  • Rovelet-Lecrux A, Hannequin D, Raux G, Le Meur N, Laquerriere A, Vital A, Dumanchin C, Feuillette S, Brice A, Vercelletto M, Dubas F, Frebourg T, Campion D (2005). "APP locus duplication causes autosomal dominant early-onset Alzheimer disease with cerebral amyloid angiopathy". Nature Genetics. 38 (1): 24–6. doi:10.1038/ng1718. PMID 16369530. 
  • Anita Rauch; Christian T. Thiel; Detlev Schindler; Ursula Wick; Yanick J. Crow; Arif B. Ekici; Anthonie J. van Essen; Timm O. Goecke; Lihadh Al-Gazali; Krystyna H. Chrzanowska; Christiane Zweier; Han G. Brunner; Kristin Becker; Cynthia J. Curry; Bruno Dallapiccola; Koenraad Devriendt; Arnd Dörfler; Esther Kinning; André Megarbane; Peter Meinecke; Robert K. Semple; Stephanie Spranger; Annick Toutain; Richard C. Trembath; Egbert Voss; Louise Wilson; Raoul Hennekam; Francis de Zegher; Helmut-Günther Dörr; André Reis (2008). "Mutations in the Pericentrin (PCNT) Gene Cause Primordial Dwarfism". Science Online: 7.