What's the relationship between trisomy 21 and down syndrome?

Cause & effect: Trisomy 21 accounts for approximately 96% of down syndrome.

One and the same.: Down syndrome or mongolism is caused by an extra chromosome 21 (trisomy 21). Affected individuals have varying degrees of neurodevelopmental delay, other associated congenital defects (e.g. Duodenal atresia, vsd, hydrocephaly) and propensity for hematological disorders and dementia of early onset - however, they tend to live long lives and may be able to be fairly independent.

Name game: Dr.Langdon Down worked at a home for the retarded in Britain in the 1800's.He was credited for the first published description of the syndrome that would carry his name. After the human chromosomes were identified and numbered in the 1950's, DS was studied and trisomy 21 was identified in most. Later studies show an extra piece of a specific area of the 21 is all that is needed to have DS.