Definition:
Down syndrome is a genetic condition in which a person has 47 chromosomes instead of the usual 46.
Alternative Names:
Trisomy 21
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.
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.
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