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Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with developmental delays, mild to moderate intellectual disability, and characteristic physical features.
Down syndrome is a chromosomal abnormality characterized by the presence of an extra copy of genetic material on chromosome 21, either in whole ( trisomy 21) or part (such as due to translocations ). The effects of the extra copy varies greatly from individual to individual, depending on the extent of the extra copy, genetic background ...
Turner syndrome ( TS ), also known as 45,X, or 45,X0, is a genetic disorder in which a person's cells have only one X chromosome or are partially missing an X chromosome ( sex chromosome monosomy ). [2] [6] Most people have two sex chromosomes (XX or XY).
There are 47 chromosomes, instead of the usual 46, giving a 47,XYY karyotype. [1] Treatment may include speech therapy or extra help with schoolwork, however outcomes are generally positive. [2] The condition occurs in about 1 in 1,000 male births. [1]
Down syndrome is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is typically associated with developmental delays, characteristic physical features, and mild to moderate intellectual disability . [2]
Jérôme Jean Louis Marie Lejeune (13 June 1926 – 3 April 1994) was a French pediatrician and geneticist, best known for his work on the link of diseases to chromosome abnormalities, most especially the link between Down Syndrome and trisomy-21 and cri du chat syndrome, amongst several others, and for his subsequent strong opposition to the ...
World Down Syndrome Day ( WDSD) is marked each year on March 21, [1] beginning in 2007. The 21st day of March (the 3rd month of the year) was selected to signify the uniqueness of the triplication ( trisomy) of the 21st chromosome which causes Down syndrome.
Recent research has identified a region of the chromosome that contains the main genes responsible for the pathogenesis of Down syndrome, located proximal to 21q22.3. The search for major genes involved in Down syndrome characteristics is normally in the region 21q21–21q22.3.
John Langdon Haydon Down (18 November 1828 – 7 October 1896) was a British physician best known for his description of the genetic condition now known as Down syndrome, which he originally classified in 1862.
Down syndrome, the most common trisomy, usually caused by an extra copy of chromosome 21 . Characteristics include decreased muscle tone, stockier build, asymmetrical skull, slanting eyes and mild to moderate developmental disability. Edwards syndrome, or trisomy-18, the second most common trisomy.
