Is Down syndrome hereditary?

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• The majority of Down syndrome cases are not hereditary. Only in cases of Translocation Down syndrome is this then possible. These inherited cases then occur because one of the parents is a carrier. A carrier will have 45 chromosomes instead of 46 but they will have all the genetic material of a person with 46 chromosomes. Remember that in Translocation Down syndrome the extra chromosome 21 material is located on a different chromosome. A carrier will have the extra material but will have only one chromosome 21. The carrier will not exhibit any of the symptoms of Down syndrome because they have the correct amount of genetic material. However, a carrier will have an increased chance of having a child with Down syndrome. If the carrier is the mother, the chances are approximately one in five of having a child with Translocation Down syndrome, but if the carrier is the father, the odds are 1 in between 20 and 50. In cases where the carrier has no unattached chromosome 21, all the carriers' children will have Down syndrome.
  
  
• The ability to have children varies among people with Down syndrome (generally they have a reduced rate of fertility). Down syndrome is also known as trisomy 21 and happens when you have three chromosomes instead of two on the 21st 'pair.' This happens when there is an error in cell division and instead of 46 chromosomes dividing into two new cells with 23 each, one of the new cells will have 24 (and therefore the extra '21' chromosome). So it's not really a hereditary thing -- the chances of giving birth to a child with Down syndrome increases after the age of 35 or so, and in general the odds are 1 in 800 of having a child with Down syndrome.

First answer by ID1961943995. Last edit by ID1961943995. Question popularity: 1 [recommend question]