How many types of Down syndrome are there?
There are three types of Down syndrome:
Trisomy 21 – in which all cells have an extra chromosome 21. About 94% of individuals with Down syndrome have this type.
Translocation – in which the extra chromosome 21 is attached to another chromosome. About 2% of individuals with Down syndrome have this type.
Mosaic – in which only some of the cells have chromosome 21. About 2% of individuals with Down syndrome have this type.
