Down syndrome is a genetic condition in which a person has 47 chromosomes instead of the usual 46.
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.
Down syndrome symptoms vary from person to person and can range from mild to severe. However, children with Down syndrome have a widely recognized characteristic appearance. The head may be smaller than normal and abnormally shaped. For example, the head may be round with a flat area on the back. The inner corner of the eyes may be rounded instead of pointed. Common physical signs include: Physical development is often slower than normal. Most children with Down syndrome never reach their average adult height. Children may also have delayed mental and social development. According to the National Institute of Child Health and Human Development, most persons with Down syndrome have mild to moderate mental retardation. Many different medical conditions are seen in babies born with Down syndrome, including Children with Down syndrome also have a higher risk for acute lymphocytic leukemia
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Reviewer Info: Rachel A Lewis, MD, FAAP, Columbia University Pediatric Faculty Practice, New York, NY, and Brian Kirmse, MD, Mount Sinai School of Medicine, Department of Human Genetics, New York, NY. Review provided by VeriMed Healthcare Network.; ADAM Health Illustrated Encyclopedia, 05/10/2007 |