Children's Hospital Colorado

Down Syndrome

What is Down syndrome?

Down syndrome is a genetic condition where an individual has three, rather than two, copies of chromosome 21. Down syndrome is the most frequently occurring chromosomal abnormality and effects one in every 691 babies born in the United States. The disorder was first identified in 1866 by John Langdon Down, a British physician, and later named after him. Today, there are more than 250,000 people living with Down syndrome in the United States.

Children who are born with Down syndrome have an increased risk for certain medical conditions such as congenital heart defects, thyroid conditions, airway and respiratory problems, vision and hearing problems, and occasionally childhood leukemia (1%). These children will also experience mild to moderate cognitive delays.

Quality educational programs, a stimulating home environment, appropriate therapies, good health care and positive support from family, friends and the community enable people with Down syndrome to develop their full potential and lead fulfilling lives.

What causes Down syndrome?

Down syndrome occurs because of the extra copy of chromosome 21, which can cause the body and brain to develop differently than a child without the syndrome.  Researchers have extensively studied the defects in chromosome 21 that cause Down syndrome. 

In 88% of cases, the extra copy of chromosome 21 is derived from the mother.  In 8% of the cases, the father provided the extra copy of chromosome 21.  In the remaining 2%, Down syndrome is due to mitotic errors, an error in cell division which occurs after fertilization when the sperm and ovum are joined. 

Who gets Down syndrome?

The incidence of Down syndrome rises with increasing maternal age.  Many specialists recommend that women who become pregnant at age 35 or older undergo testing for Down syndrome.  The likelihood that a woman under 30 who becomes pregnant will have a baby with Down syndrome is less than 1 in 1,000, but the chance of having a baby with Down syndrome increases to 1 in 400 for women who become pregnant at age 35.

A consult with a genetic counselor or geneticist is important to investigate the risk of recurrence in younger mothers. 

Helpful resources:

Global Down Syndrome Foundation
Linda Crnic Institute for Down Syndrome
Rocky Mountain Down Syndrome Association
National Down Syndrome Society
National Down Syndrome Congress
Colorado Springs Down Syndrome Association
The Arc of Colorado
Denver Adult Down Syndrome Clinic

What are the signs and symptoms of Down syndrome?  

A few of the common physical traits of Down syndrome are low muscle tone, small stature, an upward slant to the eyes, and a single transverse crease across the center of the palm – although each person with Down syndrome is a unique individual and may possess these characteristics to different degrees, or not at all.

Are there different types of Down syndrome?

There are three types of Down syndrome: trisomy 21 (nondisjunction) accounts for 95% of cases, translocation accounts for about 4% and mosaicism accounts for about 1%.

  • Trisomy 21 (Nondisjunction) happens when an extra copy of chromosome 21 is present in all cells of the body. Chromosomes contain all of the genetic information that tells our body how to grow. Most people have 46 total chromosomes (23 pairs) in every cell in their body. One chromosome of each pair comes from the father, and one chromosome of each pair comes from the mother. An extra copy of chromosome 21 causes the differences we see in people with Down syndrome.  
  • Translocation Down syndrome happens when an extra copy of chromosome 21 is attached to another chromosome. This is then present in all cells of the body.  Translocation accounts for about 4% of all cases of Down syndrome. In translocation, part of chromosome 21 breaks off during cell division and attaches to another chromosome, typically 14. While the total number of chromosomes in the cells remains 46, the presence of any extra parts of chromosome 21 causes the characteristics of Down syndrome. Translocation Down syndrome is the only type of Down syndrome that can be passed down from a parent who does not have features of Down syndrome. (A consult with a genetic counselor or geneticist is important to investigate the risk of recurrence).
  • Mosaic Down syndrome happens when an extra copy of chromosome 21 is present in some, but not all, of the body’s cells. About 1 to 2% of people with Down syndrome have mosaic Down syndrome. Mosaic Down syndrome is caused by a random event shortly after the egg and sperm join together. When cells are dividing, some cells receive an extra copy of chromosome 21. Others cells have two copies. Research has indicated that individuals with mosaic Down syndrome may have fewer characteristics of Down syndrome than those with other types of Down syndrome. 

What tests are used to diagnose Down syndrome?

Prenatally – At this time, there are two categories of tests for Down syndrome that can be performed before a baby is born: screening tests and diagnostic tests.  Prenatal screens estimate the chance of the fetus having Down syndrome.  Most of these tests provide a probability. 

Diagnostic tests can provide a definitive diagnosis with almost 100% accuracy.  Most screening tests involve a blood test and an ultrasound (sonogram).  The diagnostic procedures available for prenatal diagnosis of Down syndrome are chorionic villus sampling (CVS) and amniocentesis.  

After Birth – Down syndrome is usually identified at birth by the presence of certain physical traits: low muscle tone, a single transverse crease across the palm of the hand, a slightly flattened facial profile and an upward slant to the eyes. Because these features may be present in babies with Down syndrome, a chromosomal analysis called a karyotype is done to confirm the diagnosis. 

To obtain a karyotype, doctors draw a blood sample to examine the baby’s cells.  They use special tools to photograph the chromosomes and then group them by size, number and shape.  By examining the karyotype, doctors can diagnose down syndrome.  Another genetic test called FISH (Fluorescent In Situ Hybridization) can apply similar principles to provide an initial diagnosis of Down syndrome in a shorter amount of time.  It provides limited information about other structural chromosome abnormalities such as translocations and deletions.

How do providers at Children’s Hospital Colorado make a diagnosis?

Tests to confirm Down syndrome are often done before a baby is born through amniocentesis or chorionic villus sampling (CVS).  There are now non-invasive prenatal tests that evaluate the DNA of the fetus in the mother’s blood and it provides a high accuracy rate of a fetus having Down syndrome. In considering these prenatal tests, pretest counseling regarding these limitations is recommended.

Referral for genetic counseling is suggested for pregnant women with positive test results. Because false-positive test results can occur, confirmation with amniocentesis or CVS is recommended by the American College of Obstetricians and Gynecologists.  After birth, diagnostic evaluation begins with a thorough medical history and physical examination of your child.  

How is Down syndrome treated?

There is no cure for Down syndrome. Medical intervention involves the treatment of specific medical comorbidities or conditions – such as heart problems – that occur and need to be treated. At the Sie Center for Down Syndrome, we practice collaborative, family-centered care by working closely with other subspecialists at the Children’s Hospital Colorado to provide the best comprehensive care to our patients. As part of our multidisciplinary approach, the Sie Center works closely with:

Why choose Children’s Hospital Colorado for your child’s Down syndrome?

Experts at the Sie Center for Down Syndrome provide comprehensive care for babies, kids and young adults who have Down syndrome. Our patients range from the prenatal phase of life up to age 21. The Sie Center for Down Syndrome offers state-of-the-art treatment and evaluation by a multidisciplinary team consisting of a developmental pediatrician, nurse practitioner, nurse, physical therapy, speech therapy, feeding therapy, occupational therapy, psychologist and social worker who have over 50 years combined experience in the care and treatment of individuals with Down syndrome.

We're also closely affiliated with local and national Down syndrome organizations and Down syndrome resources to understand and meet the needs of our patients.  In addition, Children's Colorado is located on the Anschutz Medical Campus, a major medical campus that provides access to comprehensive, high-quality care for pediatric patients, as well as education and research efforts in Down syndrome.


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