What is Down Syndrome?

Down syndrome occurs when an extra copy of a chromosome is present at the time of conception. The most common form of Down syndrome is Trisomy 21, when there is an extra copy of the 21^st chromosome. Instead of the typical 2 copies of the 21^st chromosome, there are 3 copies. In Translocation Down syndrome, that extra copy of the 21^st chromosome attaches to a different set of chromosomes. Translocation is usually inherited. Mosaic Down syndrome is when pieces of the that extra 21^st chromosome attach to other sets of chromosomes.

To learn more detail about what Down syndrome is, here are some great resources:

National Down Syndrome Congress

National Down Syndrome Society

Global Down Syndrome Foundation