Fact Sheet
What is Down syndrome?
Down syndrome is a genetic disorder caused when abnormal cell division results in an extra full or partial copy of chromosome 21. This extra genetic material causes the developmental changes and physical features of Down syndrome.
Down syndrome varies in severity among individuals, causing lifelong intellectual disability and developmental delays. It's the most common genetic chromosomal disorder and cause of learning disabilities in children. It also commonly causes other medical abnormalities, including heart and gastrointestinal disorders.
• Down syndrome occurs when an individual has a full or partial copy of the 21st chromosome. Typically developing individuals have two copies of the 21st chromosome, individuals with Down syndrome have three copies.
o The cause of the extra or partial chromosome is still unknown.
• There are three types of Down syndrome o trisomy 21 (nondisjunction) accounts for 95% of cases o translocation accounts for about 4% of cases o mosaicism accounts for about 1% of cases
• Down syndrome is the most commonly occurring chromosomal condition. Approximately 1 in 772 babies in the United States are born with Down syndrome. About 5,100 babies with Down syndrome are born in the United States each year.
• Down syndrome occurs in people of all races and of all socio-economic levels.
• The incidence of Down syndrome increases with the age of the mother. But due to higher fertility rates in younger women, 51% of children with Down syndrome are born to women under 35 years of age.
• 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.
• A few of the common physical traits of Down syndrome are low muscle tone, small statue, an upward slant to the eyes, and a single deep crease across the center of the palm. Every person with Down syndrome is a unique individual and may possess these characteristics to different degrees or not at all.
• Life expectancy for people with Down syndrome has increased dramatically in recent decades- from 25 in 1983 to 60s today.
• People with Down syndrome attend school, work, participate decisions that affect them, have meaningful relationships, vote, and contribute to society in many wonderful ways.
• All people with Down syndrome experience cognitive delays, but the effect is usual 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.
For more information, visit www.ndss.org