Encyclopedia / D / Down Syndrome

Down Syndrome


Down syndrome is a combination of physical abnormalities and mental retardation characterized by a genetic defect in chromosome pair 21.

The genetic defect associated with Down syndrome is the presence of extra material on the chromosome pair designated 21. Although other genetic disorders may be associated with an extra chromosome, only Down syndrome is characterized by extra chromosome 21 material.


Down syndrome is a combination of birth defects, including some degree of mental retardation and characteristic facial features.

About 30 to 50 percent of babies with Down syndrome also have congenital heart defects, and many have some visual and hearing impairment and other health problems. The severity of all of these problems varies greatly.

Children with Down syndrome can usually do most things that any young child can do, such as walking, talking, dressing and being toilet-trained. However, they generally do these things later than other children.

Today, there are more opportunities than ever before for people with Down syndrome to attend schools, hold jobs and participate in leisure activities and relationships. Some marry, and women with Down syndrome can have children.


Down syndrome is one of the most common genetic birth defects. It affects all races and economic levels equally. Approximately 1 in 800 to 1 in 1,000 babies are born with the disorder. Life expectancy among adults with Down syndrome is about 55 years, though this varies.


A child with Down syndrome may have eyes that slant upward and small ears that may fold over a little at the top. The 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.

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

The degree of mental retardation varies widely from mild to moderate to severe. However, most fall within the mild to moderate range, and studies suggest that, with proper training, less than 10 percent will be severely mentally retarded.


The diagnosis of Down Syndrome is based upon a combination of clinical presentation and genetic testing.


There is no cure for Down syndrome, nor can it be prevented. Scientists do not know why problems involving chromosome 21 occur. Nothing either parent did, or did not do, caused Down syndrome.


What is the extent of mental retardation present?

How will the child's life be affected?

What special medical precautions are necessary?

How can we best cope? Are there local support groups?