Down Syndrome
Key points
- Down syndrome is a disorder caused by an abnormality of the chromosomes — the pieces of DNA containing the blueprint for the human body.
- In addition to the characteristic physical features and decreased mental abilities, other health problems frequently are seen in people with Down syndrome.
- Down syndrome frequently is suspected at birth based on physical appearance.
- Down syndrome is a genetic disorder due to the presence of an extra chromosome in each cell.
What Is It?
Down syndrome is a disorder caused by an abnormality of the chromosomes — the pieces of DNA containing the blueprint for the human body. Normally a person has two copies of each chromosome, but a person with Down syndrome has three copies of chromosome 21. The condition also is called trisomy 21. In a few cases, the extra copy is attached to another chromosome (translocation), or found in only some of the person's cells (mosaicism). The extra DNA produces the physical and mental characteristics of Down syndrome, which include a small head that is flattened in the back; slanted eyes; extra skin folds at the corners of the eyes; small ears, nose and mouth; short stature; small hands and feet; and some degree of mental disability. Between 3,000 and 5,000 children with Down syndrome are born each year in the United States.
Symptoms
In addition to the characteristic physical features and decreased mental abilities, other health problems frequently are seen in people with Down syndrome. These include:
- Hearing deficits
- Heart problems
- Intestinal abnormalities
- Eye problems
- Low levels of thyroid hormone
- Skeletal problems such as joint instability
- Poor weight gain in infants
People with Down syndrome develop leukemia more often than those without the disorder, and they are at increased risk of infections, problems with the immune system, skin disorders, and seizures.
Infants with Down syndrome usually develop more slowly than other children of the same age, although a wide variation is seen. Language development is typically much slower, as is motor development. For example, most toddlers walk between 12 and 14 months of age, but toddlers with Down syndrome walk between 15 and 36 months.
Diagnosis
Down syndrome frequently is suspected at birth based on physical appearance. The diagnosis usually is confirmed by a blood test to examine the chromosomes. Additional testing may be done, including chest X-rays, echocardiography and an electrocardiogram, to check for the presence of cardiac abnormalities. Sometimes X-ray studies of the gastrointestinal tract are done as well.
In some cases, Down syndrome is detected during pregnancy with the use of a blood test that measures the levels of three chemicals (a "triple-screen" test) in a pregnant woman's blood. If these results are abnormal, further tests can be done to help diagnose Down syndrome.
Expected Duration
Written and revised by
Andrey Nailor, M.D.
Our doctors write and review articles for accuracy and keep them up to date.
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