Is a chromosomal disorder that occurs in approximately 1-700 births in Canada alone. Although it is not known for sure, it is possible that an error in cell division causes this extra chromosome. This extra chromosome material was present at conception, either from the father's sperm or the mother's egg, each of which contributes 23 chromosomes. A person with Down Syndrome will have 47 chromosomes in each cell instead of 46. It is most important to know that nothing the mother or father did before or during the pregnancy that could have caused this to happen. The chances of having a child with Down Syndrome is if: you are 45 the percentage is 1-32, and if you are under 35 it goes up to 80%.
There are three types of chromosomal patterns that result in Down Syndrome. They are: trisomy 21, translocation or mosaicism. A blood test is required for chromosome analysis and the type of pattern would be determined at that time.
Ninety-five % of people with DS have trisomy 21, which means there is an extra#21 chromosome in each cell.

Two to three % of people with Down Syndrome have a translocation pattern. In translocation, during cell division, apart of the number 21 chromosome breaks off and attaches itself to another chromosome, usually the number 14 chromosome. About two-thirds of these translocations occur spontaneously while the rest are inherited from a parent. If the chromosome test shows a translocation, it is recommended the the parents have their own chromosomes analyzed as the chance of having other children with DS may increase significantly.
Approximately 2% of people with Down Syndrome have Mosaicism. In this case, a faulty cell division occurs in one of the early cell divisions after conception,resulting in some cells having 46 chromosomes and some having 47. The percentage of cells with 47 instead of 46 chromosomes, varies from person to person.