Genetics Northern California

Down Syndrome

What is Down syndrome?
How common is Down syndrome? 
What causes Down syndrome?
How is Down syndrome diagnosed?
Can Down syndrome be diagnosed during pregnancy? 
How is Down syndrome treated? 
Where can I get more information about Down syndrome?

 

Down syndrome-laughterWhat is Down syndrome?
Down syndrome is a genetic condition that usually causes delays in physical, intellectual, and language development. A person with Down syndrome also has a higher chance for birth defects and medical problems. 

Learning in Down syndrome
Intellectual disability is a part of Down syndrome, but there is a wide range of learning ability in people with this condition. Most children with Down syndrome have mild to moderate delays in their development. Early intervention therapies help with development. 

Medical concerns in Down syndrome 
Not everyone with Down syndrome has serious medical problems, but birth defects and certain medical concerns are more likely. Common medical conditions in people with Down syndrome include:

• Low muscle tone (hypotonia) – nearly 100% 

• Hearing problems – 75%

• Vision problems – 60%

• Heart defects (present at birth) – 50%

• Thyroid disease – 15%

• Intestinal defects (present at birth) – 12%

Life expectancy in Down syndrome
Due to improvements in medical care, adults with Down syndrome are reaching older ages on a regular basis. The typical life expectancy is now in the fifties to sixties.  

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How common is Down syndrome? 
About 1 out of every 700 babies is born with Down syndrome. Down syndrome happens in all races and in all populations around the world. 

Trisomy 21

What causes Down syndrome?
Down syndrome is caused by an extra chromosome 21. Normally, we have 23 pairs of chromosomes in each cell, which contain our genetic material. This includes two copies of chromosome 21, one from each parent. Most individuals with Down syndrome have three separate copies of chromosome 21 (instead of the normal two) in every cell of the body. This type of Down syndrome is called trisomy 21. It occurs randomly and does NOT run in families. Down syndrome is also NOT due to anything the mother or father did before or during pregnancy. Trisomy 21 is more likely to happen as a woman gets older, but it can occur in a woman of any age. 

There are other forms of Down syndrome, such as mosaic Down syndrome and translocation Down syndrome. Individuals with these forms of Down syndrome typically have the same features as a person with trisomy 21. The main difference is found by looking at the chromosomes in a laboratory. In a small number of cases, translocation Down syndrome can be inherited from a parent without Down syndrome. Although most cases of Down syndrome are NOT inherited, if you have a family history of Down syndrome you can contact a genetic counselor to determine your chance to have a child with Down syndrome.

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How is Down syndrome diagnosed?
Down syndrome is often suspected shortly after birth based on a baby’s appearance. The diagnosis is confirmed by taking a blood sample and studying the baby's chromosomes. Chromosome testing is extremely accurate and can tell for sure if a baby has Down syndrome. Chromosome testing is also useful in determining the chance of Down syndrome for others in the family. 

Can Down syndrome be diagnosed during pregnancy? 
Down syndrome can be diagnosed during pregnancy through diagnostic tests, such as chorionic villus sampling (CVS) and amniocentesis. These tests look directly at the chromosomes from a developing baby. 

Prenatal screening tests help look for Down syndrome during pregnancy but they do not provide a final answer. Screening tests for Down syndrome may include a blood test on the pregnant woman or an ultrasound of the developing baby. These tests estimate the risk for Down syndrome. If the risk for Down syndrome is increased, a woman is offered the option of diagnostic testing to find out for sure. 

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How is Down syndrome treated?
There is no cure for Down syndrome, but medical treatment and education programs can address many of the related problems. Health issues can be treated medically or surgically when necessary. Special education programs are available, starting in infancy, to determine areas of strengths and weaknesses and maximize a child’s learning potential.

Where can I get more information about Down syndrome? 

Down syndrome-laptopGeneral information
Medline Plus: Down syndrome - General information about Down syndrome provided by the National Library of Health and the National Institutes of Health. Extensive links to related online resources.

Parent Support Resources 
National Down Syndrome Society - Provides information and support for individuals with Down syndrome and their families.

National Mosaic Down Syndrome Association - Parent support resources specifically about mosaic Down syndrome.

Down Syndrome Connection of the Bay Area – Support organization that serves families living in the San Francisco Bay Area who have a family member with Down syndrome. 

References: 
American Academy of Pediatrics (AAP); Clinical Report – Health Supervision for Children With Down Syndrome; 2011

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Last reviewed: October 13, 2015

Reviewed by: Kimberly Barr, MS, LCGC