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?

High resolution chromosome testing

There are also a number of early prenatal blood tests that done to screen for Down syndrome but the diagnosis can only be confirmed by amniocentesis or chorionic villi sampling.

How is Down managed?

People with Down syndrome have an increased risk for certain medical conditions such as congenital heart defects, respiratory and hearing problems, Alzheimer's disease, childhood leukemia and thyroid conditions. Many of these conditions are now treatable, so most people with Down syndrome lead healthy lives. All people with Down syndrome experience cognitive delays, but the effect is usually mild to moderate and is not indicative of the many strengths and talents that each individual possesses. Quality educational programs, a stimulating home environment, good health care and positive support from family, friends and the community enable people with Down syndrome to lead fulfilling and productive lives.

The Sie Center for Down Syndrome at Children’s Hospital Colorado has a team of medical experts, therapists as well as a feeding therapist, psychologist and an education specialist to evaluate and work with your child and his family to optimize health, development and quality of life.

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

Our Sie Center for Down Syndrome is one of the most comprehensive programs for children with Down Syndrome locally, nationally and internationally. It is located at Children’s Colorado, one the top pediatric hospitals ranked by U.S. News & World Report.


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