Down Syndrome Fast Facts

Are there any other names associated with Down syndrome?
Down syndrome is also known at Trisomy 21.

What causes Down syndrome?
During normal conception, which defines the beginning of life for the baby, the mother and father each contribute 23 chromosomes – usually resulting in a child with 46 chromosomes. With most cases of Down syndrome, the baby gets an extra chromosome 21, which gives him or her 47 chromosomes. This added genetic material causes the physical and developmental conditions associated with Down syndrome.

How often does this condition occur?
Down syndrome affects approximately one of every 800 pregnancies.

How many people are affected?
There are more than 400,000 people in the United States living with Down syndrome.

Why do they call it Down syndrome?
Down syndrome was named after British doctor John Langdon Down, who first described the condition in 1887. However, the extra chromosome that causes the condition wasn’t identified until 1959.

What are some of the physical complications?
Nearly half of children with Down syndrome will have a congenital heart defect.
About half have problems with sight and hearing. These conditions are treatable, so most individuals lead healthy lives.

Does this condition affect how long a person will live?
The life expectancy of people with Down syndrome has dramatically increased from 25 years in 1983 to 60 years today.

Can Down syndrome be detected before birth?
Prenatal screening and diagnostic testing does not provide information that could be used to treat the baby before birth. It is most often used to identify unborn babies with Down syndrome and makes them targets of abortion. These tests are invasive and have a risk for the baby and other complications.

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