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World Down Syndrome Day

Boy with his head on his desk

Each year in the US, about 6,000 babies are affected by Down syndrome. Many people with Down syndrome lead productive lives well into adulthood. Learn more.

What is Down syndrome?

Down syndrome is a condition in which a baby has an extra chromosome. Chromosomes are small “packages” of genes in the body. They determine how a baby’s body forms during pregnancy and how, as the baby grows in the womb and after birth, the baby’s body functions.

Typically, a baby has 46 chromosomes. Babies with Down syndrome have an extra copy of one of these chromosomes, chromosome 21. This extra copy changes the body’s and brain’s development and can cause mental and physical problems for the baby.

How common is Down syndrome?

Down syndrome remains the most common chromosomal condition diagnosed in the U.S. From 2004-2006, the estimated national prevalence was approximately 15 per 10,000 live births. This means that Down syndrome affects 1 out of every 700 infants born in the United States.1 Prevalence at birth is the proportion of babies with Down syndrome out of the total number of live births.

Did You Know?

Not all birth defects can be prevented. But, a woman can take steps before and during pregnancy to increase her own chances of having a healthy pregnancy. Such steps include taking a daily multivitamin with folic acid (400 micrograms), not smoking, and not drinking alcohol during pregnancy.

Learn about other steps »

What problems do some people with Down syndrome have?

People with Down syndrome can have physical problems as well as intellectual disabilities. Even though people with Down syndrome might have some physical and mental features in common, every baby born with Down syndrome is different, and symptoms can range from mild to severe. Some examples of physical problems associated with Down syndrome include a birth defect of the heart or problems with the stomach, hearing, skeleton, intestines, thyroid, or eyes. People with Down syndrome usually have an IQ in the mild-to-moderate range of intellectual disabilities. People with Down syndrome also typically have delayed language development or difficulties with physical coordination. Babies and children with Down syndrome often will benefit from special therapies that help to improve their physical and intellectual limitations, including speech therapy, occupational therapy, and physical therapy. Children with Down syndrome usually also need extra help or attention in school. Many people with Down syndrome lead productive lives well into adulthood.

What causes Down syndrome?

Research has identified some factors that increase the risk for having a baby with Down syndrome, such as maternal age greater than 35 years.2-4 However, the majority of babies with Down syndrome are born to mothers less than 35 years, because there are many more births among younger women.5, 6 In most cases, no one knows for sure why Down syndrome occurs or how many factors play a role.

Where can I find resources for families and individuals affected by Down syndrome?

  1. Parker SE, Mai CT, Canfield MA, et al. Updated National Birth Prevalence Estimates for Selected Birth Defects in the United States, 2004-2006. Birth Defects Res A. 2010;88:1008-16.
  2. Allen EG, Freeman SB, Druschel C, Hobbs CA, O’Leary LA, Romitti PA, et al. Maternal age and risk for trisomy 21 assessed by the origin of chromosome nondisjunction: a report from the Atlanta and National Down Syndrome Projects. Hum Genet. 2009 Feb;125(1):41-52.
  3. Ghosh S, Feingold E, Dey SK. Etiology of Down syndrome: Evidence for consistent association among altered meiotic recombination, nondisjunction, and maternal age across populations. Am J Med Genet A. 2009 Jul;149A(7):1415-20.
  4. Sherman SL, Allen EG, Bean LH, Freeman SB. Epidemiology of Down syndrome. Ment Retard Dev Disabil Res Rev. 2007;13(3):221-7.
  5. Adams MM, Erickson JD, Layde PM, Oakley GP. Down’s syndrome. Recent trends in the United States. JAMA. 1981 Aug 14;246(7):758-60.
  6. Olsen CL, Cross PK, Gensburg LJ, Hughes JP. The effects of prenatal diagnosis, population ageing, and changing fertility rates on the live birth prevalence of Down syndrome in New York State, 1983-1992. Prenat Diagn. 1996 Nov;16(11):991-1002.
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