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Down syndrome - Overview

Alternative Names

Trisomy 21

Definition of Down syndrome:

Down syndrome is a genetic condition in which a person has 47 chromosomes instead of the usual 46.

Causes, incidence, and 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.

Reviewed last on: 10/18/2010
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.

References

ACOG Committee on Practice Bulletins. ACOG Practice Bulletin No. 77: screening for fetal chromosomal abnormalities. Obstet Gynecol. 2007 Jan;109(1):217-227.

AAP Committee on Genetics. Health supervision for children with Down syndrome. Pediatrics. 2001 Feb;107(2):442-449.

Davidson MA. Primary care for children and adolescents with Down syndrome. Pediatr Clin North Am. 2008;55:1099-1111.

Simpson JL, Otaño L. Prenatal genetic diagnosis. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics:Normal and Problem Pregnancies. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2007:chap 7.

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