Alternate Names : Trisomy 21
Down syndrome is a genetic condition in which a person has 47 chromosomes instead of the usual 46.
Overview, Causes, & Risk Factors
In most cases, Down syndrome occurs when there is an extra copy of chromosome 21. This form of Down syndrome is called Trisomy 21. The extra chromosome causes problems with the way the body and brain develop.
Down syndrome is the most common single cause of human birth defects.
Review Date : 5/12/2009
Reviewed By : Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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