History of Down syndrome
English physician John Langdon Down first characterized Down syndrome as a distinct form of mental retardation in 1862, and in a more widely published report in 1866 entitled "Observations on an ethnic classification of idiots". Due to his perception that children with Down syndrome shared physical facial similarities (epicanthal folds) with those of Blumenbach's Mongolian race, Down used the terms mongolism and mongolian idiocy. Idiocy was a medical term used at that time to refer to a severe degree of intellectual impairment. Down wrote that monoglism represented "retrogression," the appearance of Mongoloid traits in the children of allegedly more advanced Caucasian parents.

# Down syndrome and society in the early 20th century
By the 20th century, "mongolian idiocy" had become the most recognizable form of mental disease. Most people with it were institutionalized. Few of the associated medical problems were treated, and most died in infancy or early adult life. With the rise of the eugenics movement, a number of states (33 of the 48 United States) and countries began programs of involuntary sterilization of individuals with Down syndrome and comparable degrees of disability. The ultimate expression of this type of public policy was the German euthanasia program "Aktion T-4" begun in 1940. Court challenges and public revulsion at the nature of these programs led to discontinuation or repeal of such programs during the decades after World War II. Even voluntary institutionalization of children with Down syndrome has become rare in Western countries.
Until the middle of the 20th century, the cause of Down syndrome remained unknown, although the presence in all races, the association with older maternal age, and the rarity of recurrence had been noticed. Standard medical texts assumed it was due to a combination of inheritable factors which had not been identified. There was some expert opinion that it might result from trauma occurring during pregnancy.
With the discovery of karyotype techniques in the 1950s it became possible to identify the obvious abnormalities of chromosomal number or shape. In 1959, Professor Jerome Lejeune discovered that Down's syndrome resulted from an extra chromosome.  The extra chromosome was subsequently labeled as the 21st, and the condition as trisomy 21. The labeling of chromosome 21 represented an unintentional deviation from the genetic convention by which the 22 pairs of autosomes comprising the human karyotype were numbered from largest to smallest (excluding the sex chromosomes). Lejeune identified the extra chromosome in mongolism as the second smallest, hence 21. Although it was later determined that chromosome 22 is actually slightly larger than 21, it was deemed too confusing to change either the numbering of the two chromosomes or name of the trisomy.

# Naming
In 1961, a group of nineteen geneticists wrote to the editor of The Lancet suggesting that mongolian idiocy had "misleading connotations," had become "an embarrassing term" and should be changed.  The Lancet supported Down's Syndrome.  The World Health Organization (WHO) officially dropped references to mongolism in 1965 after a request by the Mongolian delegate. However, almost 40 years later, the term mongolism still appears in some medical texts.
In 1975, the United States National Institute of Health convened a conference to standardize the nomenclature of malformations.  They recommended eliminating the possessive form: "The possessive use of an eponym should be discontinued, since the author neither had nor owned the disorder."  While both the possessive and non-possessive forms are used in the general population, Down syndrome is the accepted term among professionals in the USA, Canada and other countries, while Down's syndrome continues to be used in the United Kingdom and other areas.

# Notes
-  Down, J.L.H. (1866). "Observations on an ethnic classification of idiots". Clinical Lecture Reports, London Hospital. 3: 259262. Retrieved 2006-07-14..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"\"""\"""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{display:none;font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em} For a history of the disorder, see Conor, Ward. "John Langdon Down and Down's syndrome (1828 - 1896)". Retrieved 2006-06-02.
-  "John Langdon Down: The Man and the Message". Down Syndrome Research and Practice. 6 (1): 1924. 1999. Retrieved 2006-06-02. Unknown parameter |Author= ignored (|author= suggested) (help)
-  Warkany, J. (1971). Congenital Malformations. Chicago: Year Book Medical Publishers, Inc. pp. 313314. ISBN 0-8151-9098-0.
-  "Jerome Lejeune Foundation". Retrieved 2006-06-02.
-  Allen, Gordon, C.E. Benda, J.A. Book, C.O. Carter, C.E. Ford, E.H.Y. Chu, E. Hanhart, George Jervis, W. Langdon-Down, J. Lejeune, H. Nishimura, J. Oster, L.S. Penrose, P.E. Polani, Edith L. Potter, Curt Stern, R. Turpin, J. Warkany, and Herman Yannet (1961). "Mongolism (Correspondence)". The Lancet. 1 (7180): 775.CS1 maint: Multiple names: authors list (link)
-  Howard-Jones, Norman (1979). "On the diagnostic term "Down's disease"". Medical History. 23 (1): 102104. PMID 153994.
-  See Review of Medical Physiology, 2005, by Professor William Ganong and General and Systematic Pathology, 2004, edited by Professor Sir James Underwood
-  A planning meeting was held on 20 March 1974, resulting in a letter to The Lancet."Classification and nomenclature of malformation (Discussion)". The Lancet. 303 (7861): 798. 1974. The conference was held 10-11 February 1975, and reported to The Lancet shortly afterward, "Classification and nomenclature of morphological defects (Discussion)". The Lancet. 305 (7905): 513. 1975.
-  Leshin, Len (2003). "What's in a name". Retrieved 2006-05-12.