Trisomy 21 (Down syndrome) is a chromosomal disorder caused by an error in cell division that results in the presence of an additional third chromosome 21. It is the most frequent genetic cause of mild to moderate cognitive disabilities and is highly associated with several medical conditions including heart defects, congenital hypothyroidism, intestinal problems, hearing loss and vision disorders, and early-onset Alzheimer’s disease.

The article Down syndrome, a closer look offers a comprehensive list of links to information on Trisomy 21.

For more information on Trisomy 21 visit

• NICHD Nation Institute of Child Health & Human Development
• March of Dimes Foundation
• Medline Plus U.S. National Library of Medicine

Ending a Wanted Pregnancy stories about Trisomy 21 (Down syndrome)