http://www.kidshealth.org/parent/medical/genetic/down_syndrome.html
http://www.mayoclinic.com/health/down-syndrome/DS00182/DSECTION=3
http://www.kidshealth.org/parent/medical/genetic/down_syndrome.html
http://www.healthscout.com/ency/68/449/main.html#SymptomsofDownSyndrome
http://www.emedicinehealth.com/down_syndrome/page5_em.htm
http://www.mayoclinic.com/health/down-syndrome/DS00182/DSECTION=7
Tuesday, April 22, 2008
What is Down Syndrome?
Down syndrome is a condition in which extra genetic material causes delays in the way a child develops, and often leads to mental retardation. It affects 1 in every 800 babies born. It is a condition in which there is extra sets of a chromosome.
What Causes Down Syndrome?
Down syndrome is caused by extra genetic material from chromosome 21 of the 23 chromosomes. There are three different causes for down syndrome. The first is Trisomy 21, which causes over 90 percent of down syndrome cases. In this case, there are three copies of chromosome 21, and is caused by abnormal cell division during development of the egg or sperm. The second type is mosaic down syndrome. This form is very rare, and it is caused by some cells (but not all) containing extra copies of chromosome 21. It is caused by abnormal cell division after fertilization. The last type is translocation down syndrome. This is when additional material from chromosome 21 becomes attached to other chromosomes.
How is Down Syndrome Inherited?
Down syndrome is actually not inherited, it is caused by abnormal cell division sometime during the reproductive cycle. Translocation down syndrome can be passed from parent to child, but it is extremely rare. A child's risk of inheriting this type of down syndrome is only 3-12 percent.
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