Down syndrome

or Down's syndrome

  1. a genetic disorder, associated with the presence of an extra chromosome 21, characterized by mild to severe mental impairment, weak muscle tone, shorter stature, and a flattened facial profile.

Origin of Down syndrome

First recorded in 1960–65; after John L. H. Down (1828–96), British physician
  • Also called trisomy 21 .

usage note For Down syndrome

Down syndrome (or Down's syndrome ) has replaced earlier terms, such as mongolism to refer to the disease and Mongoloid or Mongol to refer to the affected person, all of which are now considered offensive.

Words Nearby Down syndrome Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use Down syndrome in a sentence

Scientific definitions for Down syndrome

Down syndrome

[ doun ]

  1. A congenital disorder caused by the presence of an extra 21st chromosome. People with Down syndrome have mild to moderate mental retardation, short stature, and a flattened facial profile. The syndrome is named after its discoverer, British physician John Langdon Haydon Down (1828-1896).

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.