Translocation Down syndrome is a type of Down syndrome that is caused when one chromosome breaks off and attaches 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 that are caused by Down syndrome. In translocation Down syndrome, the extra 21 chromosome may be attached to the 14 chromosome, or to other chromosome numbers like 13, 15, or 22. In some cases, two 21 chromosomes can be attached to each other.

A small number of babies born with Down syndrome have translocation Down syndrome. There are no big differences between the patients who have translocation Down syndrome compared with those who have 3 separate copies of chromosome 21. This is 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 or not. 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 normal and 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:

  • Have trouble getting pregnant

  • Suffer miscarriages

  • Have an increased chance of having a child with health problems

The parent can donate the right amount of chromosomes to a pregnancy. However, 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 rearrangement and 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 and, therefore, 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.