Down Syndrome (cont.)

Medical Author:

Sietske N. Heyn, PhD

Sietske N. Heyn, PhD

Sietske N. Heyn is a medical writer with a PhD in neuroscience. Dr. Heyn's education includes a BS with honors from the University of Oregon, and a doctoral degree in neuroscience from the University of California at Davis. After completing postdoctoral training at the University of California, San Francisco, and many years of working as a medical writer at the Stanford University Center for Down Syndrome Research, Dr. Heyn now runs her own medical writing business.

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Medical Editor:

David Perlstein, MD, MBA, FAAP

David Perlstein, MD, MBA, FAAP

Dr. Perlstein received his Medical Degree from the University of Cincinnati and then completed his internship and residency in pediatrics at The New York Hospital, Cornell medical Center in New York City. After serving an additional year as Chief Pediatric Resident, he worked as a private practitioner and then was appointed Director of Ambulatory Pediatrics at St. Barnabas Hospital in the Bronx.

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In this Article

• What is Down syndrome?
• What are the chromosome basics of Down syndrome?
• How do the extra genes lead to Down syndrome?
• What are the risk factors for conceiving a child with Down syndrome?
• What are the characteristic features and symptoms of Down syndrome?
• What type of prenatal screening is available for Down syndrome?
• How is the diagnosis of Down syndrome made?
• What about cognitive impairment in Down syndrome?
• What other conditions are associated with Down syndrome?
• How is Down syndrome managed?
• What about early intervention and education for Down syndrome?
• What are the needs of infants and preschool children with Down syndrome?
• How do adolescents with Down syndrome develop?
• What should one expect for adults with Down syndrome?
• Do individuals with Down syndrome work?
• Where can I find clinical trials for Down syndrome?
• Down Syndrome At A Glance
• Where can I find more information about Down syndrome?
• Patient Comments: Down Syndrome - Experience
• Patient Comments: Down Syndrome - Symptoms
• Down Syndrome Index

Exactly how the extra genes from chromosome 21 lead to Down syndrome is still not clear. Scientists believe that the increased presence of specific genes alters the interaction between these and other genes. Some genes will become more active and others less active than normal, leading to changes in the development and maintenance of the body. Why some individuals are more severely affected than others might have to do with how many and which specific extra genes were inherited.

Scientists are trying to find out which genes from chromosome 21, when present in three copies, are responsible for the different characteristics of Down syndrome. Currently, about 400 genes on chromosome 21 have been identified, but the functions of most are still unknown. Through human studies and animal models, scientists are making progress in understanding the functions of individual genes.

The only well known risk factor for conceiving a child with Down syndrome is advanced maternal age. The older the woman is at conception, the greater the risk of having a child with Down syndrome.

Mother's age at conception Risk of Down syndrome

• 25 years 1 in 1,250
  
  
• 30 years 1 in 1,000
  
  
• 35 years 1 in 400
  
  
• 40 years 1 in 100
  
  
• 45 years 1 in 30

Parents who have conceived a child with Down syndrome have a 1% increased risk of conceiving another child with Down syndrome. If a parent is a carrier of a chromosome 21 translocation, the risk can be as high as 100%.

Women with Down syndrome have a 50% risk of conceiving a child with Down syndrome. If the father has Down syndrome, the risk of conceiving a child with Down syndrome is also increased.