This information has been produced by the Northern Genetics Service for families where a condition called a ‘balanced translocation’ has been found. We hope it will answer some of your questions.
What is a chromosome?
Chromosomes are present in every cell of our body and they contain the information the body needs to develop and function properly. This information is carried in genes that are arranged along the chromosomes.
How many chromosomes do we have?
There are usually 46 chromosomes in every cell. These chromosomes come in pairs, one from our mother and one from our father.
The chromosomes can be sorted into 23 pairs by looking at them down a microscope.
How are chromosomes different if you have a balanced translocation?
Most people who have a balanced translocation have the right amount of chromosome material but it has been rearranged in some way. This may happen if two chromosomes swap pieces (a reciprocal translocation). In other cases two whole chromosomes may become stuck together (a Robertsonian translocation). This page describes what happens when someone has a reciprocal translocation.
How does this affect me?
About 1 in 500 people have a balanced translocation. Usually this has no effect on their development or general health because no genes have been lost or gained.
Translocations can, however, cause problems when having a family. Most translocation carriers can have perfectly normal children but some are at greater risk of losing pregnancies or, less commonly, having children with some form of disability.
How do translocations cause problems?
People inherit one chromosome from their mother and one from their father to make up a matched pair of chromosomes. If one parent has a chromosome that has been rearranged it may be passed on. There are four possible combinations:
Can I find out which of these possibilities will happen?
Sometimes we can give people an idea of what is most likely to happen by knowing which chromosomes are involved and how they are rearranged. There are tests that can be done in pregnancy to check the baby's chromosome pattern.
Is a balanced translocation always inherited?
When someone is found to have a balanced translocation the most likely explanation is that it has come from one of the parents. However, occasionally a balanced translocation occurs which is not present in either of the parents. This is known as a de novo balanced translocation. This is a new rearrangement that probably occurred in the egg cell or sperm cell before the baby was conceived.
Do I have to tell other members of my family?
Because a balanced translocation may be inherited and because people are unaware they have a balanced translocation there may be other members of the family who have it as well. It is important that they have the opportunity to find out. You may wish to tell them yourself or we can arrange an appointment with you and your relatives to help with this.
You may have further questions
If so please contact:
Northern Genetics Service
Institute of Genetic Medicine
International Centre for Life
Newcastle upon Tyne NE1 3BZ
Tel: 0191 241 8600