Down syndrome is an abnormality of the chromosomes and not genic in origin .This occurs in one of every two thousand newborns. People do not "carry" this and the child is born with three rather than two chromosomes numbered 21. The mother and father of the child are normal except in the rare case of a woman with Down syndrome who gives birth to a child; the copying or replication error occurs either in the germ cell or in the initial cell division of the embryo.
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http://www.ds-health.com/risk.htm
Having a sibling with Down syndrome does not directly increase the chances of giving birth to a child with Down syndrome. The risk is influenced by maternal age, not family history. If both parents are carriers of the genetic translocation for Down syndrome, the risk may be higher.
That is hard to say because the frequency of Down syndrome if a function of maternal age so it is not fixed. A mom between 20 and 24 years old has a 1/ 1400 risk of having a child with Down syndrome. A mom who is 45 or older has a 1/25 risk. Overall, it is fair to say Down syndrome is one of the most common and best known genetic disease. Other genetic disease such as Cystic Fibrosis, hemochromatosis are also common. The frequency of all these things varies in different populations as well as age. So the question is quite hard to answer without isolating a specific population.
0-9 purcent
1 out of every 691 live births
For the United States, estimated as the fraction of people in the population with the syndrome, ~1/5500.
1 in every 1,000 babies that is born. 1 is the Down syndrome and 1,000 is the people that dont.
Down syndrome occurs in people of all races; however, studies have shown that people of Caucasian descent have a higher incidence of Down syndrome compared to other races. This is likely due to differences in genetic makeup and population demographics.
down syndrome
There are approximately7,222,222 people with down syndrome in the world ( if you compare the stat 1 in every 800-1000 births to the world's population of 6.5 billion).
The prevalence of Down Syndrome worldwide is estimated to be around 1 in 1,000 live births. This prevalence can vary depending on factors such as maternal age. With advances in medical care and increased awareness, individuals with Down Syndrome are living longer, contributing members of society.