Down syndrome is a condition in which a baby is born with 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. Normally, a baby is born with 46 chromosomes. Babies born with Down syndrome have an extra copy of one of these chromosomes. This extra copy changes the body’s and brain’s normal development and causes mental and physical problems for the baby.

Even though people with Down syndrome might have some physical and mental features in common, symptoms of Down syndrome can range from mild to severe. Usually, mental development and physical development are slower in people with Down syndrome than in those without it.

Some common physical signs of Down syndrome include:

• A flat face with an upward slant to the eye, a short neck, small ears, and a large tongue
• Tiny white spots on the iris (colored part) of the eye
• Small hands and feet
• A single crease across the palm of the hand
• Small pinky fingers that sometimes curve toward the thumb
• Poor muscle tone or loose ligaments

To learn more about Down Syndrome click on one of the following links or scroll down the page.

What We Know About Down Syndrome

• How often does Down syndrome occur?
• What problems do children with Down syndrome have?

What We Still Do Not Know About Down Syndrome

• What causes Down syndrome?
• Can Down syndrome be prevented?

Resources for Families and Individuals Affected by Down Syndrome

How often does Down syndrome occur?

CDC estimates that each year about 3,357 babies in the United States are born with Down syndrome (1). In other words, about 13 of every 10,000 babies born in the United States each year is born with Down syndrome.

What problems do children with Down syndrome have?

Babies and adults with Down syndrome can have physical problems, as well as intellectual disabilities. Every baby born with Down syndrome is different. In addition to the physical signs, some might have major birth defects or other medical problems. However, many people with Down syndrome live happy, productive lives well into adulthood.

Still, some physical problems associated with Down syndrome include:

• A birth defect of the heart
• Stomach problems, such as a blocked small intestine
• Celiac disease, a digestive disease that damages the small intestine so that nutrients from food are not absorbed well
• Problems with memory, concentration, and judgment, often called dementia
• Hearing problems
• Eye problems, such as cataracts or trouble seeing objects that are close by (far-sighted)
• Thyroid problems
• Skeletal problems

A person with Down syndrome can have an IQ in the mild-to-moderate range of mental retardation. He or she also mighty have delayed language development and difficulties with physical coordination.

[Return to Top]

What causes Down Syndrome?

To understand Down syndrome, it is necessary to understand how a baby develops. Each baby starts developing when he or she receives 23 chromosomes from the mother’s egg and 23 chromosomes from the father’s sperm. When a baby has Down syndrome, an error happened when either the egg or the sperm was formed. This error caused an extra chromosome (called chromosome number 21) in the egg or sperm, so that the baby received a total of 24 instead of 23 chromosomes from one of its parents. Therefore, the baby ends up having 47 chromosomes in every cell of his or her body, instead of 46 chromosomes. This extra chromosome causes the physical signs and additional problems that can occur among people with Down syndrome. The causes of the errors that produces the extra chromosome is not known.

The age of the mother is the only factor that has been shown to increase the risk of having a baby with Down syndrome. This risk increases with every year, especially after the mother is 35 years of age. However, because younger women are more likely to have babies than older women, 80% of babies with Down syndrome are born to women younger than 35 years of age.

CDC works with many researchers to study the risk factors that can increase the chance of having a baby with Down syndrome. Following are examples of what this research has found:

• The number of babies with Down syndrome seems to be increasing, especially among mothers older than 35 years of age (2).
• Certain factors seem to influence how long a person with Down syndrome will live, including ethnicity, low weight at birth, and whether the baby was born with a heart defect (3).
• Death rates among Black or African-American infants with Down syndrome seem to be higher than death rates among White infants with Down syndrome (4).

Can Down Syndrome be prevented?

There is no known way to prevent the Down syndrome. However, infants and children with Down syndrome often will benefit from special programs that help to improve their physical and mental limitations. These include speech therapy, occupational therapy, and exercises for physical coordination. Children with Down syndrome usually also need extra help or attention in school.

While there is currently no way to prevent Down syndrome, mothers can take steps before and during pregnancy to have a healthy pregnancy. Steps include taking a daily multivitamin with folic acid (400 micrograms), not smoking, and not drinking alcohol during pregnancy.

[Return to Top]

National Down Syndrome Society

National Association for Down Syndrome

Medline

Mayo Clinic


References

1. Canfield MA, Honein MA, Yuskiv N, Xing J, Mai CT, Collins JS, et al. National estimates and race/ethnic-specific variation of selected birth defects in the United States, 1999-2001. Birth Defects Res A. 2006;76(11): 747-56.
2. Besser LM, Shin M, Kucik JE, & Correa A. Prevalence of Down syndrome among children and adolescents in metropolitan Atlanta. Birth Defects Res A. 2007;79: 765-74.
3. Rasmussen SA, Lee-Yang Wong MS, Correa A, Gambrell D, and Friedman JM. Survival in infants with Down syndrome, metropolitan Atlanta, 1979-1998. Pediatrics. 2006;148: 806-12.
4. Shin M, Kucik JE, Correa A. Causes of death and case fatality rates among infants with Down syndrome in metropolitan Atlanta. Birth Defects Res A. 2007;79: 775-80.
   

[Return to Top]

Date: March 11, 2009
Content source: National Center on Birth Defects and Developmental Disabilities