| Signs and symptoms |
Children with Down syndrome have a distinct facial appearance — small head, small ears, flat face and upward slanting eyes. The fingers are relatively short, and the hand often has a single crease in the palm. These infants also tend to have a "floppy" muscle tone. Infants born with Down syndrome may be of average size, but typically they grow slowly and remain small.
| Causes |
Down syndrome is caused by one of three types of abnormal cell division that involves the 21st chromosome pair of the 23 pairs of chromosomes found in all normal human cells. These types of abnormalities include:
- Nondisjunction. Faulty chromosome division during formation of the egg or sperm results in
an embryo with three rather than two chromosome 21s. This accounts for nearly 95 percent of all cases
of Down syndrome.
- Translocation. During chromosome division a part of chromosome 21 separates and attaches to
another chromosome. About 3 percent to 4 percent of all cases are due to translocation.
- Mosaicism. Abnormal cell division in the early life of an embryo results in some cells with the normal 46 chromosomes, although others have 47, creating a mosaic of normal and abnormal cells. This accounts for 1 percent to 2 percent of all cases.
| Risk factors |
A woman's chances of giving birth to a child with Down syndrome increase with age. Because a woman's eggs age, there's a greater inclination for chromosomes to divide improperly. Although researchers are experimenting with ways to test a woman's likelihood to produce improper chromosome division, there is no test for Down syndrome before conception.
With more women delaying childbearing, doctors continue to be concerned about the increased incidence of Down syndrome. Despite this increased incidence, the risk that a woman 35 years of age or older will conceive a baby with Down syndrome has remained the same during the past several decades. The increase in the incidence of Down syndrome births is due to the increase in the number of births to women older than 35 during the past few decades.
| Screening and diagnosis |
Screening tests during pregnancy
Screening tests that are generally performed at 15 to 18 weeks into a pregnancy can help identify an increased possibility of Down syndrome.
Tests such as the triple or quadruple analytic blood tests identify concentrations of certain biochemical markers, such as human chorionic gonadotropin (HCG), alpha-fetoprotein (AFP) and estriol in the mother's bloodstream. However, a positive result on a screening test doesn't mean that Down syndrome is present. It simply identifies pregnancies that might warrant additional or more invasive tests.
A normal blood-screening test done during pregnancy doesn't guarantee that the fetus doesn't have Down syndrome, only that the likelihood is reduced. In fact, only 60 percent of babies with Down syndrome are identified by an abnormal blood-screening test.
Diagnostic tests during pregnancy
If a pregnancy-screening test is positive and suggests an increased likelihood of Down syndrome, further testing might be considered. These tests can confirm a suspicion of Down syndrome in the fetus.
Diagnostic tests for identification of Down syndrome include:
- Amniocentesis. A sample of the amniotic fluid surrounding the fetus is withdrawn through a
needle inserted into the mother's uterus. This sample is then used to analyze the chromosomes of the
fetus. This test usually is performed between 15 and 20 weeks of gestation, although it can be done as
early as 12 weeks. The test is 98 percent to 99 percent accurate and carries a risk of miscarriage
ranging from 1 in 200 to 1 in 400.
- Chorionic villus sampling (CVS). Cells are taken from the mother's placenta through the abdominal wall or cervix. These cells can be used to analyze the fetal chromosomes. Typically performed between the 10th and 12th week of pregnancy, this test is 98 percent to 99 percent accurate and carries a risk of miscarriage of 1 in 100.
More detailed ultrasound examination using high-resolution or color-Doppler ultrasound imaging can identify conditions such as congenital heart disease or gastrointestinal blockage that may be associated with Down syndrome. Such conditions might require newborn intensive care or surgery shortly after birth. However, the majority of fetuses with Down syndrome won't have distinctive abnormalities that your doctor can identify by ultrasound. Therefore, ultrasound isn't sensitive enough to be a substitute for amniocentesis or CVS in diagnosing Down syndrome.
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| Complications |
About 40 percent of children with Down syndrome have some type of congenital heart defect. These heart problems can be life-threatening and may require surgery in early infancy. These children may also be at increased risk of developing of a variety of problems, including gastrointestinal blockage, respiratory infections, thyroid problems, hearing loss, poor vision or leukemia.
Intellectual development will be impaired for children with Down syndrome. The degree of mental retardation ranges from mild to moderate. Many children with Down syndrome are happy, loving and easygoing. However, some children develop behavior problems, such as anger, resistance to conformity and unwillingness to obey.
About 1 in 4 people with Down syndrome will develop Alzheimer's disease, compared with about 1 in 16 in the general U.S. population. Average life expectancy for those with Down syndrome is 55, but that largely depends on the severity of health problems.
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| Coping strategies |
There is no medical cure for Down syndrome. Early detection and correction of heart defects or gastrointestinal problems often is possible. Intervention programs, in which children with Down syndrome are stimulated at an early age with appropriate sensory, motor and cognitive activities, can make a difference in the development of skills. A loving, caring relationship between parents and a child — later an adolescent — with Down syndrome can have a positive effect on the child's emotional development.
Helping with the child's school activities might reveal individual abilities, such as a tendency to learn more readily with visual rather than auditory information. Also, children with Down syndrome may have greater understanding than their language skills might indicate.
Many people with Down syndrome live with loving families, go to school, learn to read and write, and perform at various levels of jobs as adults. Most are able to live productive and fulfilling independent or semi-independent lives.
Many cities have support groups for parents of children with Down syndrome. Support groups for parents are also available on the Internet.
— July 31, 2001 —