Down Syndrome

Cause

Down syndrome is caused by abnormal cell division in early fetal development. Medical experts believe it most often starts in a woman's egg before or at conception. Less often, the error occurs in sperm at conception. It is not known what causes the cells to divide abnormally.

Genes grouped together make up chromosomes. Normally, a child inherits 46 chromosomes, 23 from each parent. The abnormal cell division related to Down syndrome produces extra genetic material, usually an extra chromosome. Down syndrome is classified according to the specific way that extra genetic material is produced. Translocation-type Down syndrome is sometimes passed down through families (inherited).

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Author:	Debby Golonka, MPH	Last Updated: August 9, 2007
Medical Review:	Adam Husney, MD - Family Medicine Michael J. Sexton, MD - Pediatrics David Smith, MD - Family Medicine
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