Down syndrome
Overview
Down syndrome, or Down's syndrome, trisomy 21, is a chromosomal condition caused by the presence of all or part of an extra 21st chromosome
Chromosome 21 (human)
Chromosome 21 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. The trisomy of the 21st chromosome causes Down Syndrome...

. It is named after John Langdon Down
John Langdon Down
John Langdon Haydon Down was a British doctor best known for his description of a relatively common genetic disorder that is now called Down syndrome.-Education:...

, the British
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 physician
Physician
A physician is a health care provider who practices the profession of medicine, which is concerned with promoting, maintaining or restoring human health through the study, diagnosis, and treatment of disease, injury and other physical and mental impairments...

 who described the syndrome
Syndrome
In medicine and psychology, a syndrome is the association of several clinically recognizable features, signs , symptoms , phenomena or characteristics that often occur together, so that the presence of one or more features alerts the physician to the possible presence of the others...

 in 1866. The condition was clinically described earlier in the 19th century by Jean Etienne Dominique Esquirol in 1838 and Edouard Seguin
Edouard Seguin
Édouard Séguin was a physician and educationist who was born in Clamecy, Nièvre. He is remembered for his work with children having cognitive impairments in France and the United States....

 in 1844. Down syndrome was identified as a chromosome 21 trisomy
Trisomy
A trisomy is a type of polysomy in which there are three copies, instead of the normal two, of a particular chromosome. A trisomy is a type of aneuploidy .-Description and causes:...

 by Dr.
 
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