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Q: What is Down Syndrome? |
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A:Down Syndrome is a chromosomal disorder that results in mild to severe learning disabilities and physical symptoms that include a small skull, extra folds of skin under the eyes, and a flattened nose bridge. Muscle tone throughout the body is usually low. Down syndrome occurs in about 1 out of every 800 births worldwide. In the United States each year, about 1,600 babies are born with this condition.
Causes: Down syndrome results when a person inherits all or part of an extra copy of chromosome 21. This can occur in many ways and the causes are unknown. The most common chromosomal abnormality that causes Down syndrome (about 95 percent of all cases) is Trisomy 21, a defect in which a third copy of chromosome 21 is present in every cell. The risk of Trisomy 21 is directly related to the age of the mother. The number of Down Syndrome births is relatively low for younger mothers but the risk significantly increases in later childbearing years. 18-year-old mothers; about 1 in 2,100, 30-year-old mothers; about 1 in 1,000, and 40-year-old mothers; about 1 in 100. Two other chromosomal abnormalities cause Down syndrome and occur in about 2 to 3 percent of all cases. Translocation is when a child inherits a small, extra piece of the 21st chromosome that is attached to another chromosome. If, in addition to the translocation, two normal 21st chromosomes are also present, the person will have some of the features of Down syndrome. If there is only one normal 21st chromosome, the person will not display symptoms but his/her children may inherit Down syndrome. Mosaic Down Syndrome results when only some cells in the body have an extra chromosome. |
