Main Entry: Down syndrome

Variant(s): or Down's syndrome

Function: noun

: a congenital condition characterized by moderate to severe mental retardation, upward slanting eyes usually with epicanthic folds, a broad short skull, broad hands with short fingers, decreased muscle tone, and by trisomy of the human chromosome numbered 21—called also trisomy 21

Down \ˈdau̇n\ , 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. His classification was invalid, but one kind of moderate to severe mental retardation came to be known as mongolism, although it is now called Down syndrome or Down's syndrome.