Is Down syndrome hereditary

Answer 1

• 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.
• It is mostly caused by an accident of gene formation. A small percent is hereditary.
• It is a genetic abnormality, but not inherited, per se.

Answer 2

Many "siblings" of people with DS often ask themselves if they are more likely to have children with DS than those who don't have people with DS in their family. To answer this question it's better to know a few general medical facts. There are three types of DS. The first form is trisomy 21 due to "nondisjunction" and accounts for about 95% of all cases of DS. In this case the extra chromosome is present in the sperm or in the egg, or in the first cellular division and, as a consequence, each cell that forms will have three chromosomes in the couple 21. This form is strictly linked to maternal age not to hereditary genetic factors. The second form of DS, which is also the least common, is the mosaicism. This represents about 2% of cases. In this form of trisomy 21 the cellular division occurs in a defective way after fertilisation, during the second or third division, or those following. As a consequence, not all the cells of the embryo that is forming contain an extra chromosome. This form also does not depend on hereditary factors. The third form, which is very rare, is partial trisomy 21 due to Robertsonian Translocation, accounts for 2-3% of cases. In this case a part of 21st chromosome breaks up during the cellular division, "moves" and attaches itself to another chromosome, usually the 14th chromosome or the other 21st chromosome. Some extra genetic material is present in both cases. About 2/3rds of translocation occur spontaneously during fertilisation. The translocation is hereditary from one of the two parents in 1/3rd of cases. In this case we have the only form of DS which is linked to a genetic factor from either the father or the mother. The parent who is the carrier of this is normal, but two of his/her chromosomes are united in a way that the total number of his/her chromosomes is only 45 instead of 46. It is important to identify, through the child's karyotype the presence or not of partial trisomy 21 due to translocation because if one of the parents is a carrier the chances that other children with DS can be born into that family are higher. So, it is advisable that the parents, the other children without DS and the blood relatives of the carrier parent have their chromosomes mapped. So, in conclusion, we can say that the chances of a brother or sister of someone with DS having children with DS are only minutely higher than those with no case of DS in their family, and concern only the form of translocation. Therefore, it is important to determine whether the brother/sister has got this form and, in this case, whether they are healthy carrier. The chromosome map or "karyotype" can be carried out on a simple blood test. Together with the blood test you can ask for a "genetic consultancy", that is a more precise and personalised explanation.

Answer 3

Down syndrome is not technically inherited. It is a genetic oops caused by an egg or a sperm having two 21st chromosomes, each egg/sperm is only supposed to have 1 copy of each chromosome so that when the two combine the child gets two of each chromosome.

Answer 4

Yes, it is possible. Males who have this disorder are almost always infertile. Females have very low conception rates and have many miscarriages. Half of their offspring have the disorder as well.

This is a mistake where the chromosomes didn't divide as they should in formation of gametes. When these divide, one of each pair of the 26 moves into each gamete. Instead of one chromosome number 21, two are in a gamete. When these met with another gamete from the other partner, the result will be 3 number 21 chromosomes. This produces the symptoms associated with Down's. This is also called Trisomy 21.

Other Trisomy disorders do not live beyond the first few weeks of pregnancy.

Answer 5

Yes, down syndrome is due to heredity. It's caused by an extra X chromosome.

Answer 6

No, it cannot.