Translocation Down Syndrome
Translocation Down syndrome is a type of Down syndrome that is caused when a chromosome 21 becomes attached to another chromosome. In this case, there are three 21 chromosomes, but one of the 21 chromosomes is attached to another chromosome. The genetic material from the extra 21 chromosome is what causes the health problems in people with Down syndrome. In translocation Down syndrome, the extra 21 chromosome may be attached to the 14 chromosome. Or it could be attached to other chromosome numbers like 13, 15, or 22. Two 21 chromosomes can be attached to each other in some cases.
A small number of babies born with Down syndrome have translocation Down syndrome. There are no big differences between the children who have translocation Down syndrome compared with those who have 3 separate copies of chromosome 21 (called trisomy 21).
Whenever a translocation is found in a child, the parents’ chromosomes are looked at to find out whether the translocation was inherited. If one parent has the translocation chromosome, then the healthcare provider knows the baby inherited the translocation from that parent. That parent will actually have 45 total chromosomes in each cell of the body, but the parent will be healthy. This is because that parent still has only two copies of each chromosome, but two of these chromosomes are attached to each other. When a person has a rearrangement of chromosome material with no extra or missing chromosome material, the person is said to have a balanced translocation. That person can also be a balanced translocation carrier.
Parents with balanced translocations may:
The parent can donate the right number of chromosomes to a pregnancy. But that parent also has a risk of donating too much or too little genetic material to a pregnancy. This is not something the parent can control or predict. The chance depends on the type of chromosome shift. It also depends on which chromosomes are involved.
There is another important thing to remember when a parent is found to have a translocation. The parents' siblings may also have inherited the translocation. They may have the same risks for problems with a pregnancy. For this reason, people with chromosome rearrangements should share this information with their relatives so that they can have the option of having their chromosomes studied.