What is Down Sydrome?

Down Syndrome is a disorder that includes a combination of birth defects. Among them, some degree of mental delay, characteristic facial features, and often heart defects, increased infections, problems with vision and hearing, and other health problems. The severity of all these problems varies greatly among the affected individuals. DS is one of the most common genetic birth defects. It is generally caused by an extra chromosome.

According to the National Down Syndrome Society, there are approximately 350,000 with DS in this country.

What causes Down Syndrome?

Normally, each egg and sperm cell contains 23 chromosomes. The union of these creates 23 pairs, or 46 chromosomes in total. Sometimes, an accident occurs when an egg or sperm cell contributes the extra chromosome 21 to the embryo, Down Syndrome results. All the features and birth defects associated with Down Syndrome result from having this extra chromosome 21 in each of the body's cells.

Down Syndrome is also called Trisomy 21 because of the extra presence of the three number 21 chromosome. Occasionally, the extra chromosome 21 is attached to another chromosome in the egg or sperm; this may result in what is called "Translocation Down Syndrome". This is the only form of DS that can be inherited from a parent. In such cases, the parent has a rearrangement of chromosome 21, called a balanced translocation, which does not affect his or her health.

Rarely, a form of DS called Mosaic DS may occur when an accident in cell division occurs after fertilization. Affected individuals have some cells with extra chromosome 21 and others with the normal number.

What health problems might a child with Down Syndrome have?

Almost half of babies with DS have heart defects. Some defects are minor and may be treated with medications, while others may require surgery. All babies with DS should be examined by a pediatric cardiologist, a doctor who specializes in heart diseases of children, and have an echocardiogram in the first 2 months of life so that any heart defects can be treated. About 10% of babies with DS are born with intestinal malformations that require surgery. More than 50% have some visual or hearing impairment. Common visual problems include crossed eyes, near or far sightedness and cataracts. Most can be improved with glasses, surgery or other treatments.

A pediatric opthalmologist should be consulted, usually within the first 6 months of life. Children with DS may have hearing loss due to fluid in the middle ear, a nerve defect or both. Babies with DS should be screened for hearing loss at birth or by 3 months of age. Children with DS tend to have many colds and ear infections, as well as bronchitis and pneumonia. They also are at increased risk of thyroid problems and leukemia.

Helpful Information and Resources

National Down Syndrome Society
666 Broadway
New York, NY 10012

National Down Syndrome Congress
1370 Center Drive, Suite 102
Atlanta, GA 30338

Band of Angels

Special Times 4 Special Friends

Parent to Parent WA State

Definitions provided by:
March of Dimes