Down syndrome causes
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Syed Hassan A. Kazmi BSc, MD [2]
Overview
Down's syndrome (DS) is caused due to the presence of an extra 21st chromosome (triplication of chromosome 21). 95 percent of DS cases are due to meiotic non-disjunction during meiosis I. 4 percent of DS cases arise due to Robertsonian translocation and very rarely DS may be caused a post-fertilization mitotic error (mosaicism).
Causes
Down's syndrome is caused by triplication of chromosome 21 (trisomy 21). The aneuploidy may occur in three possible ways:
- Meiotic nondisjunction of homologous chromosomes
- From improper division of chromosomes during meiosis I or meiosis II. One gamete will end up with extra 21st chromosome.[1][2]
- Robertsonian translocation
- Individuals with normal number of chromosomes but an extra portion of 21st chromosome.[3][4][5]
- Mosaicism
- Post-fertilization mitotic error[6][7]
For a detailed description on the mechanisms leading to Down's syndrome, click here
References
- ↑ Antonarakis SE (March 1991). "Parental origin of the extra chromosome in trisomy 21 as indicated by analysis of DNA polymorphisms. Down Syndrome Collaborative Group". N. Engl. J. Med. 324 (13): 872–6. doi:10.1056/NEJM199103283241302. PMID 1825697.
- ↑ Antonarakis SE, Petersen MB, McInnis MG, Adelsberger PA, Schinzel AA, Binkert F, Pangalos C, Raoul O, Slaugenhaupt SA, Hafez M (March 1992). "The meiotic stage of nondisjunction in trisomy 21: determination by using DNA polymorphisms". Am. J. Hum. Genet. 50 (3): 544–50. PMC 1684265. PMID 1347192.
- ↑ Hook EB (October 1984). "Parental age and unbalanced Robertsonian translocations associated with Down syndrome and Patau syndrome: comparison with maternal and paternal age effects for 47, +21 and 47, +13". Ann. Hum. Genet. 48 (Pt 4): 313–25. PMID 6238567.
- ↑ Zhao WW, Wu M, Chen F, Jiang S, Su H, Liang J, Deng C, Hu C, Yu S (2015). "Robertsonian translocations: an overview of 872 Robertsonian translocations identified in a diagnostic laboratory in China". PLoS ONE. 10 (5): e0122647. doi:10.1371/journal.pone.0122647. PMC 4416705. PMID 25932913.
- ↑ Petersen MB, Adelsberger PA, Schinzel AA, Binkert F, Hinkel GK, Antonarakis SE (September 1991). "Down syndrome due to de novo Robertsonian translocation t(14q;21q): DNA polymorphism analysis suggests that the origin of the extra 21q is maternal". Am. J. Hum. Genet. 49 (3): 529–36. PMC 1683126. PMID 1831959.
- ↑ Hsu LY, Gertner M, Leiter E, Hirschhorn K (November 1971). "Paternal trisomy 21 mosaicism and Down's syndrome". Am. J. Hum. Genet. 23 (6): 592–601. PMC 1706744. PMID 4257130.
- ↑ Modi D, Berde P, Bhartiya D (June 2003). "Down syndrome: a study of chromosomal mosaicism". Reprod. Biomed. Online. 6 (4): 499–503. PMID 12831601.