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Lulu --------------------------------- Original Article: http://www.mayoclinic.com/invoke.cfm?id=DS00182 Down syndrome Overview Down syndrome is a genetic disorder that results in varying degrees of physical and mental retardation. The condition varies in severity, causing developmental problems that range from mild to severe. The disorder occurs as a result of extra genetic material. In most people, the genes are contained on 23 pairs of chromosomes, for a total of 46 chromosomes. Most people with Down syndrome have an extra copy of the No. 21 chromosome, for a total of 47 chromosomes. Down syndrome is the most common chromosomal disorder. An estimated 1 in 800 infants are born with Down syndrome. Down syndrome is also a common cause of miscarriage. Every year, as many as 5,000 babies are born with Down syndrome in the United States. Signs and symptoms Children with Down syndrome have a distinct facial appearance. Though not all children with Down syndrome have the same features, some of the more common features are: Flattened facial features Protruding tongue Small nose Upward slanting eyes Unusually shaped ears Children with Down syndrome may also have: Poor muscle tone A single crease in the palm Relatively short fingers Excessive flexibility Infants born with Down syndrome may be of average size, but typically they grow slowly and remain smaller than other children of similar age. Causes Human cells normally contain 23 pairs of chromosomes. One chromosome from each pair comes from the father, the other from the mother. Down syndrome is caused by one of three types of abnormal cell division that involves the 21st chromosome. These abnormalities include: Trisomy 21. Faulty chromosome division during formation of the egg or sperm results in an embryo with three rather than two chromosome 21s. This accounts for 92 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, while others have 47, creating a mosaic of normal and abnormal cells. This accounts for 2 percent to 4 percent of all cases. There are no known behavioral or environmental factors that cause Down syndrome. 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. At 35 the chance a woman will have a child with Down syndrome is one in 400. At 40, it's one in 105. By age 49, the risk of having a child with Down syndrome jumps to one in 12. With more women delaying childbearing, doctors continue to be concerned about an increasing incidence of Down syndrome. Typically, a mother who has one child with Down syndrome has about a one in 100 chance of having another child with Down syndrome. Screening and diagnosis There's currently no way to screen for Down syndrome before pregnancy. Screening tests during pregnancy Doctors generally perform screening tests that can help identify if your fetus has an increased possibility of Down syndrome around the 16th week of pregnancy. Blood tests such as the triple screen or the maternal serum alpha-fetoprotein (MSAFP) test identify concentrations of certain biochemical markers, such as human chorionic gonadotropin (HCG), alpha-fetoprotein (AFP) and estriol, in the mother's bloodstream. When a fetus has Down syndrome, these values can be altered from those that occur in a normal pregnancy. However, a positive result on a screening test doesn't mean that your baby has Down syndrome. It simply identifies the possibility, which may warrant further investigation with 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, you might consider further testing. These tests may 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. Doctors usually perform this test between 14 and 18 weeks of gestation. The test carries a risk of miscarriage ranging from one in 200 to one in 400, and it may take as long as two weeks for results. Chorionic villus sampling (CVS). Cells taken from the mother's placenta can be used to analyze the fetal chromosomes. Typically performed between the 10th and 12th week of pregnancy, this test carries a risk of miscarriage of one in 100. Test results may be available in as little as two days, though it commonly takes a week or longer for final results. Percutaneous umbilical blood sampling (PUBS). Blood is taken from a vein in the umbilical cord and examined for chromosomal defects. Doctors generally perform this test after 20 weeks of gestation. These three tests are all between 98 percent and 99 percent accurate in diagnosing Down syndrome before birth. Researchers are working on developing less-invasive methods of detecting Down syndrome before birth using blood tests or ultrasound. Diagnostic tests for newborns After birth, the initial diagnosis of Down syndrome is often based on the baby's appearance. Your doctor will probably order a test called a karyotype if your child displays some or all of the characteristics of Down syndrome. A karyotype is an analysis of your child's chromosomes. If there's an extra chromosome 21 present in all or some of the cells, the diagnosis is Down syndrome. Complications Nearly 50 percent of children with Down syndrome have some type of 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 a variety of other health conditions, including gastrointestinal blockage, thyroid problems, hearing loss or poor vision. Other complications may include: Leukemia. Young children with Down syndrome have 10 to 15 times the risk of developing leukemia as do children who don't have Down syndrome. Infectious diseases. Children with Down syndrome are much more susceptible to infectious diseases because of abnormalities in their immune systems. Their risk of contracting pneumonia is 62 times as high as it is for children who don't have Down syndrome. Additionally, children with this disorder have a 12-fold chance of dying of an infectious disease. Impaired intellectual development. Intellectual development is impaired for children with Down syndrome. The degree of mental retardation ranges from mild to moderate. Dementia. Later in life, people with Down syndrome have a greatly increased risk of dementia. Symptoms of dementia often appear before age 40 for people with Down syndrome. Life spans have increased dramatically for people with Down syndrome. In 1929, a baby born with Down syndrome often didn't live to age 10. By 1983, that figure was 25 years. Today, someone with Down syndrome can expect to live to 40 and beyond, depending on the severity of his or her health problems. Coping skills There's 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, may improve the development of skills. Many people with Down syndrome live with their families, go to school, learn to read and write, and perform at various levels of jobs as adults. Many are able to live productive and fulfilling independent or semi-independent lives. Many communities have support groups for parents of children with Down syndrome. Support groups are also available on the Internet. By Mayo Clinic staff DS00182 September 02, 2003 © 1998-2004 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved. A single copy of these materials may be reprinted for noncommercial personal use only. 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