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Down syndrome or Down's syndrome, [12] also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. [3] It is usually associated with developmental delays, mild to moderate intellectual disability, and characteristic physical features.
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.
The average IQ of a young adult with Down syndrome is 50, equivalent to the mental age of an 8- or 9-year-old child, but this number varies widely. [3] At the same time, they enjoy a rich social and emotional awareness. [4] Down syndrome is the most common chromosome abnormality in humans, [3] occurring in about one per 1000 babies born each ...
An anaphase lag of a chromosome 21 in a Down syndrome embryo leads to a fraction of euploid cells (2n cells), phenomenon described as "aneuploidy rescue". There is considerable variability in the fraction of cells with trisomy 21, both as a whole and tissue-by-tissue. This is the cause of 1–2% of the observed Down syndromes. [4]
Down syndrome is a genetic condition in which people are born with an extra copy of chromosome 21. This extra copy affects the development of the body and brain, causing a range of physical and mental impairments for the individual. Fragile X syndrome, most frequent among males, is thought to cause autism and intellectual disability.
Down Syndrome is a genetic disorder that was first described in 1866 by British doctor John L. Down. [2] It was discovered to be caused by an extra chromosome by French pediatrician Jérôme Lejeune in July 1958, less than two years before Tricia was born. [3] Medical advice in 1960 was typically to institutionalize children with Down Syndrome.
Some of the undersigned are inclined to replace the term Mongolism by such designations as 'Langdon Down Anomaly', or 'Down's Syndrome or Anomaly', or 'Congenital Acromicria'. Several of us believe that this is an appropriate time to introduce the term 'Trisomy 21 Anomaly', which would include cases of simple Trisomy as well as translocations.
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