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In most cases, Down syndrome occurs when there is an extra copy of chromosome 21. This form of Down syndrome is called Trisomy 21.
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The disease is caused by trisomy 21, meaning their bodies' cells have an extra chromosome 21.(© Lester V. Bergman/Corbis.).
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In approximately one to two percent of Down syndrome cases, the original egg and sperm cells contain the correct number of chromosomes, 23 each. The problem occurs sometime shortly after fertilization—during the phase when cells are dividing...
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Down syndrome is usually the result of an extra copy of chromosome 21(trisomy 21). As described earlier, Down syndrome may occur because of: nondisjunction within the sperm, or more commonly, the egg cell; genetic mosaicism, which occurs after con...
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In approximately one to two percent of Down syndrome cases, the original egg and sperm cells contain the correct number of chromosomes, 23 each. The problem occurs sometime shortly after fertilization—during the phase when cells are dividing...
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While Down syndrome is a chromosomal disorder, a baby is usually identified at birth through observation of a set of common physical characteristics. Babies with Down syndrome tend to be overly quiet, less responsive, with weak, floppy muscles.
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Detailed information on trisomy 21, also called Down syndrome, including cause, diagnosis, prevention, and research
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Detailed information on trisomy 21, also called Down syndrome, including cause, diagnosis, prevention, and research
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