Facts:

Ninety-five percent of people with Down

syndrome have an extra #21 chromosome

in every cell of their body. This is known

as trisomy 21.

Three to four percent have an additional

#21 chromosome attached to another

chromosome. This is called translocation

Down syndrome. In this case, a parent may

be a carrier of a balanced translocation.

About one percent of people with Down

syndrome have an extra #21 chromosome

in some cells, but not in others. This is

called mosaic Down syndrome.