Down Syndrome Report

        The chromosomal abnormality involved in most cases of Down syndrome is trisomy-21, or the presence of three copies of the 21st chromosome. As a result, the affected person has 47 chromosomes in all body cells instead of the normal 46, although how this causes the condition's symptoms is not yet known. Scientists assume that the reason for the abnormal chromosomal assortment is the fertilization of an ovum having 24 chromosomes by a sperm with a normal assortment of 23, …

…mother. The incidence of Down syndrome in children born to 25-year-old mothers is approximately 1 in 1200; the risk increases to approximately 1 in 350 for 35-year-olds and approximately 1 in 120 for women older than 40 years. Prenatal tests can be used to detect chromosome abnormality causing Down syndrome. SOURCES 1) 'Down Syndrome,' Microsoft(R) Encarta(R) 96 Encyclopedia. (c) 1993-1995 Microsoft Corporation. All rights reserved. (c) Funk & Wagnalls Corporation. All rights reserved. 2) 'Down Syndrome,' Encyclopedia of Sleep and Dreaming.