Down Syndrome 4

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is called "Down's" in Europe.
In the first part of the twentieth century, there was much speculation of
the cause of Down syndrome. The first people to speculate that it might be
due to chromosomal abnormalities were Waardenberg and Bleyer in the
1930s. But it wasn't until 1959 that Jerome Lejeune and Patricia Jacobs,
working independently, first determined the cause to be trisomy of the 21st
chromosome. Cases of Down syndrome due to translocation and mosaicism
were described over the next three years.
The estimated incidence of Down syndrome is between 1 in 1,000 to 1
in 1,100 live births. Each year approximately 3,000 to 5,000 children are born
with this chromosome disorder. It is believed there are about 250,000 families
in the United States who are affected by Down syndrome.

Mode of Inheritance
Although many theories have been developed, it is not known what
actually causes Down syndrome. Some professionals believe that hormonal
abnormalities (X-rays, ...

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