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Down syndrome is a genetic abnormality resulting in the birth of person with typical skeletal appearance resembling persons native to Mongolia and China, and being mentally challenged to a variable degree, with predisposition to certain diseases, and a slightly shorter than normal life span. (We must never refer to the disorder as Mongolism). Last updated November 11, 2013
The disability is named after a physician named John Langdon Down. In the year 1866, he gave the first description of this group of diseases, which therefore bears his name. He differentiated between mental retardation due to thyroid disease (Cretinism) and the genetic disorder, which he described as "Mongoloids" because these children looked like people from Mongolia. Later, due to ethnic protests, the term "Mongoloid" was dropped and the name Down Syndrome became established.
The cause of Down Syndrome was established in 1959 by Lejeune and Patricia Jacobs, working independently. They found that it was due to triplication (instead of duplication) of the Human Chromosome number 21. (The genetic code is composed of 46 chromosomes arranged as 23 pairs). This condition is called Trisomy 21, and may be due to:
The second and third conditions, where some cells have Trisomy while others have a normal duplication, is called Mosaicism.
For details on genetics, see our genetics page.
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