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WordNet Dictionary
[n]  a congenital disorder caused by having an extra 21st chromosome; results in a flat face and short stature and mental retardation
 Synonyms: Down's syndrome, mongolianism, mongolism, trisomy 21
 See Also: backwardness, birth defect, congenital abnormality, congenital anomaly, congenital defect, congenital disorder, mental retardation, retardation, slowness, subnormality, trisomy



Medical Dictionary
 Definition: A disorder caused by the presence of an extra chromosome 21 and characterized by mental retardation and distinguishing physical features.
Biology Dictionary
  1. An uncommon (1 in 1000 births) congenital disorder in which a person is born with three copies of chromosome 21. It is more common among children born to mothers over the age of 35. People with this disorder have physical and mental retardation to varying degrees and typically have facial defects, vision, respiratory and cardiac problems. This disorder was formerly known as mongolism.
  2. Physical characteristics of a person with Down's syndrome include small and short head, flat nasal bridge, reddish cheeks, dry lips, large, protruding tongue, small ears, epicanthal folds, and short neck. Mental retardation and hypotonia are also major symptoms, the degree of which varies with individuals. There is also a high incidence of congenital heart diseases and duodenal atresia. With good support, persons with this syndrome can develop their full potential. An Alzheimer-like dementia often occurs in the fourth and fifth decades and leads to a shortened life expectancy.

    The chromosomal abnormality is diagnostic. In 95% of cases, trisomy 21 is present (one extra chromosome 21), and in the rest which has the usual 46 chromosomes present, there is an abnormal translocation involving chromosome 21.