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Unformatted text preview: (after fertilization). Mosaic Down Syndrome is likely to be less severe because some of the cells are normal. Trisomy 18 (Edward Syndrome) The incidence of Trisomy 18 is approximately 1 out of every 3000 live births. Trisomy 18 is associated with mental and physical retardation, skull and facial abnormalities, defects in all organ systems, and poor muscle tone. Mean survival is 2 to 4 months. Less than 10% survive to 1 year; a few survive to their 20s or 30s. Trisomy 13 (Patau Syndrome) The incidence of Trisomy 13 is is approximately 1 out of 16,000 live births. Trisomy 13 produces mental and physical retardation, skull and facial abnormalities, and defects in all organ systems. It is also associated with a left lip, a large, triangular nose, and extra digits. Eighty percent die in the first month, five to ten percent live past the first year....
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- Fall '10