By being a part of the Stepping Stones family, you will learn first hand the information provided here and more.

What is Down syndrome?

Down syndrome is caused by extra genetic material from chromosome 21. Chromosomes are the structures in cells that contain the genes. There are three tyes of Down syndrome: Trisomy 21, Translocation, and Mosaicism.

Each person normally has 23 pairs of chromosomes or 46 in all. An individual inherits one chromosome per pair from the mother's egg and one from the father's sperm. When an egg and sperm cell join together, they normally form a fertilized egg with 46 chromosomes.
The three types of Down syndromes are as follows:

Trisomy 21
A developing egg or sperm cell may divide incorrectly, sometimes resulting in an egg or sperm cell with an extra chromosome number 21. When this cell joins with a normal egg or sperm cell, the resulting embryo has 47 chromosomes instead of 46. Down syndrome also is called trisomy 21 because affected individuals have three number 21 chromosomes, instead of two. This type of error in cell division causes about 95 percent of the cases of Down syndrome


Occasionally, before fertilization, a part of chromosome 21 breaks off during cell division and becomes attached to another chromosome in the egg or sperm cell. The resulting embryo may have what is called translocation Down syndrome. Affected individuals have two normal copies of chromosome 21 plus extra chromosome 21 material attached to another chromosome. This type of error in cell division causes about 3 to 4 percent of the cases of Down syndrome.  In some cases, the parent has a rearrangement of chromosome 21, called a balanced translocation, which does not affect his or her health.

About 1 to 2 percent of individuals with Down syndrome have a form called mosaicism.  In this form, the error in cell division occurs after fertilization. Affected individuals have some cells with an extra chromosome 21 and others with the normal number.

How common is Down syndrome?

Down syndrome is one of the most common genetic birth defects, affecting about 1 in 800 babies (1). According to the National Down Syndrome Society, there are approximately 350,000 individuals with Down syndrome in the United States (2).

What causes Down syndrome?

Down syndrome is caused by extra genetic material from chromosome 21. Chromosomes are the structures in cells that contain the genes.

Each person normally has 23 pairs of chromosomes, or 46 in all. An individual inherits one chromosome per pair from the mother's egg and one from the father's sperm. When an egg and sperm cell join together, they normally form a fertilized egg with 46 chromosomes. (see What is Down syndrome for more information)

What health problems might a child or adult with Down syndrome have?

The outlook for individuals with Down syndrome is far brighter than it once was. Most of the health problems associated with Down syndrome can be treated.  Individuals with Down syndrome are more likely than unaffected individuals to have one or more of the following health conditions:

  • Heart defects
  • Intestinal defects
  • Vision problems
  • Hearing loss
  • Infections
  • Thyroid problems, leukemia and seizures
  • Adult Memory loss

Some individuals with Down syndrome may have a number of these problems, while others may have none. The severity of these conditions varies greatly.

What does a baby/child with Down syndrome look like?

You will also notice that your baby will look like he belongs in your family. He will look like his brothers and sisters although he will likely have some of the physical characteristics associated with Down syndrome, as well. These physical characteristics include eyes that slant upward and small ears that may fold over a little at the top. The child's mouth may be small, making the tongue appear large. The nose also may be small, with a flattened nasal bridge. Some babies with Down syndrome have short necks and small hands with short fingers. Having less muscle tone, they may appear somewhat “floppy.”

The child or adult with Down syndrome is often short and has unusual looseness of the joints. Most children with Down syndrome have many, but not all, of these features.

Are there different degrees of Down syndrome?

This is a frequent question. When one asks about the word “degree” it is assumed the person is asking how much of a cognitive impairment or developmental delay the person with Down syndrome will have. A person with Down syndrome will have a cognitive impairment as a result of having the disability. The degree of cognitive impairment and or developmental delay may range from mild to severe based on the individual’s own genetic make-up, early intervention, therapy, and support. It is more typical that an individual’s cognitive delay will be in the mild to moderate range of functioning.

What can a child with Down syndrome do?

Children with Down syndrome usually can do most things that any young child can do, such as walking, talking, dressing and being toilet-trained. However, they generally start learning these things later than other children. The exact age that these developmental milestones will be achieved cannot be predicted. However, early intervention programs, like the Stepping Stones Early Intervention Program, beginning in infancy can help these children achieve their developmental milestones sooner than without intervention.

Can a child with Down syndrome go to school?

Yes. There are special programs beginning in the preschool years to help children with Down syndrome develop skills as fully as possible. Along with benefiting from early intervention and special education, many children are integrated into the regular classroom. Refer to the information about the Stepping Stones School in this website. Many children with Down syndrome learn to read and write, and some graduate from high school and go on to post-secondary programs or college. Individuals with Down syndrome participate in diverse childhood activities both at school and in their neighborhoods.

Can Down syndrome be cured or prevented?

There is no cure for Down syndrome, nor is there any way to prevent it. However, some studies suggest that women who have certain variant genes that affect how their bodies metabolize (process) the B vitamin folic acid may be at increased risk for having a baby with Down syndrome (4, 5).

Does the risk of Down syndrome increase with the mother's age?

Yes. The risk of Down syndrome increases from about 1 in 1,250 at age 25, to 1 in 1,000 at age 30, 1 in 400 at age 35, 1 in 100 at age 40 and 1 in 30 at age 45 (6). Women over age 35 have been traditionally considered most likely to have a baby with Down syndrome. However, about 80 percent of babies with Down syndrome are born to women who are under age 35, as younger women have far more babies (2).

What is the risk that parents of a child with Down syndrome will have another affected child?

In general, in each subsequent pregnancy, the chance of having another baby with Down syndrome is 1 percent plus whatever additional risk a mother has, based upon her age (2, 7). If, however, the first child has translocation Down syndrome, the chance of having another child with Down syndrome may be greatly increased.

Can Down syndrome be diagnosed before the child is born?

Yes. The American College of Obstetricians and Gynecologists (ACOG) recommends that all pregnant women be offered a screening test for Down syndrome, regardless of the woman's age. Screening may consist of a maternal blood test done in the first trimester (at 11 to 13 weeks of pregnancy), along with a special ultrasound examination of the back of the baby's neck (called nuchal translucency), or a maternal blood test done in the second trimester (at 15 to 20 weeks) (8). A screening test helps identify pregnancies that are at higher-than-average risk of Down syndrome. However, a screening test cannot diagnose Down syndrome or other birth defects.
Women who have an abnormal screening test result are offered a diagnostic test, such as amniocentesis or chorionic villus sampling (CVS). These tests are highly accurate at diagnosing, or more likely, ruling out Down syndrome.

ACOG also recommends that pregnant women of all ages have the option of bypassing the screening test and choosing a diagnostic test for Down syndrome instead (8). Until recently, only women over age 35 and others considered at increased risk for having a baby with Down syndrome were offered diagnostic testing because amniocentesis and CVS pose a very small risk of miscarriage.
Most parents-to-be receive reassuring news from a screening or diagnostic test for Down syndrome. However, if a prenatal diagnostic test shows that the baby has Down syndrome, parents have an opportunity to prepare medically, emotionally and financially for the birth of a child with special needs, such as arranging for delivery in a medically appropriate setting.

Can people with Down syndrome have children?

With rare exceptions, men with Down syndrome cannot father a child (3). In any pregnancy, a woman with Down syndrome has a 50-50 chance of conceiving a child with Down syndrome, but many fetuses are miscarried.

Is the MArch of Dimes conducting reseArch on Down syndrome?

Some MArch of Dimes grantees are investigating why errors in chromosome division occur, in the hope of someday preventing Down syndrome and other birth defects caused by abnormalities in the number or structure of chromosomes. Other grantees are investigating the role of specific genes in causing the brain abnormalities associated with Down syndrome, with the goal of treating the mental retardation associated with the disorder. An international team of scientists has mapped all the genes of chromosome 21. This information eventually may pave the way for treatment of many features of this disorder.

Are there other organizations conducting reseArch on Down syndrome?

Yes. In particular, the Down Syndrome ReseArch and Treatment Foundation whose mission is, “To stimulate biomedical reseArch that will accelerate the development of treatments to significantly improve cognition for individuals with Down syndrome.” For more information, please visit

Where can families affected by Down syndrome get additional information?

In addition to the information in this website, The Stepping Stones Programs have a wealth of knowledge. In addition, there are organizations across the country that provide information and support for families with children affected by Down syndrome. Two are:

National Down Syndrome Society - 666 Broadway New York, NY 10012 (800) 221-4602 or (212) 460-9330 Web site:

National Down Syndrome Congress - 1370 Center Drive, Suite 102 Atlanta, GA 30338
(800) 232-NDSC or (770) 604-9500 Web site:


1 - Centers for Disease Control and Prevention (CDC). Birth Defects: Frequently Asked Questions. Updated 12/12/06.
2 - National Down Syndrome Society. Information Topics. Accessed 1/11/07..
3 - American Academy of Pediatrics Committee on Genetics. Health Supervision for Children with Down Syndrome. Pediatrics, volume 107, number 2, February 2001, pages 442-449.
4 - O'Leary, V.B., et al. MTRR and MTHFR Polymorphism: Link to Down Syndrome? American Journal of Medical Genetics, January 15, 2002, volume 107, number 2, pages 151-155.
5 - Scala, I., et al. Analysis of Seven Maternal Polymorphisms of Genes Involved in Homocysteine/Folate Metabolism and Risk of Down Syndrome. Genetics in Medicine, volume 8, number 7, July 2006, pages 409-416.
5 - American College of Obstetricians and Gynecologists (ACOG). Your Pregnancy and Birth, 4th Edition. ACOG, Washington, DC, 2005.
6 - National Institute of Child Health and Human Development (NICHD). Facts About Down Syndrome. Last updated 8/18/06.
7 – American College of Obstetricians and Gynecologists (ACOG). Screening for Fetal Chromosomal Abnormalities. ACOG Practice Bulletin, number 77, January 2007.

© 2008 MArch of Dimes Foundation. All rights reserved. The MArch of Dimes is a not-for-profit organization recognized as tax-exempt under Internal Revenue Code section 501(c)(3). Our mission is to improve the health of babies by preventing birth defects, premature birth, and infant mortality.