There are three types of Down Syndrome. All have similar if not identical traits – though severity may vary, and often the difference cannot be told their physical or behavioral characteristics alone.
The most common type of Down Syndrome is Trisomy 21.
Trisomy 21 accounts for 95% of Down Syndrome cases, marked by each cell in the body having a third copy of the 21st chromosome – which can come from either the mother or father.
The second type is Translocation Down Syndrome.
Translocation Down Syndrome accounts for about 3% of cases. In these cases, an extra part or whole 21st chromosome exists as part of ANOTHER chromosome, rather than as a separate third chromosome. It is translocated to another.
The third type is Mosaic Down Syndrome.
Mosaic Down Syndrome affects about 2% of those with Down Syndrome. With Mosaic Down Syndrome, only some, not all, cells of the body display the third 21st chromosome. Often, these individuals have fewer features of the condition, depending on how many cells are affected.