or  Down syndrome  n :  a congenital condition characterized by moderate to severe mental retardation, slanting eyes, a broad short skull, broad hands with short fingers, and by trisomy of the human chromosome numbered 21 - called also Down's , trisomy 21 
 
Down, John Langdon Haydon (1828-1896), British physician. Down published in 1866 a treatise on the degeneration of race as a result of marriages of consanguinity. He classified individuals exhibiting mental retardation according to the supposed physiognomic features of various races including the American Indian, Caucasian, Ethiopian, and Mongolian. Although his classification is invalid, one kind of moderate to severe mental retardation was known until recently as mongolism and is now called Down's syndrome or Down syndrome.
 
 
 
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