Down syndrome is caused by a person having three copies of chromosome 21 instead of two copies. This is why Down syndrome is also referred to by the name Trisomy 21. Instead of a pair of chromosomes, as is found in all the other chromosomes, number 21 includes three chromosomes. It is important to understand that all of the chromosomes of this person are normal. It is the fact that there is an extra chromosome that causes Down syndrome. Every cell in a person with Down syndrome will contain 47 chromosomes (with the exception of Mosaic Down syndrome) instead of 46 chromosomes.
Note: There are currently no drugs listed for "Down Syndrome".
