Handbook of Genetic Counseling/Balanced Translocation

Balanced Translocation Introduction and Contracting Can you explain in your own words what you understand about why you were referred to genetics? What are your main concerns for ______ at this time? Do you have any specific questions you would like us to make sure we try to answer? Outline session Take medical and family history Review the chromosome results with you Explain more about why we want to do chromosome testing on you (parents) Dr Viskochil will examine him We will then make sure to discuss any further questions or concerns Medical/Developmental History follow form that I started filling out and confirm info Family History 3 generation pedigree include standard questions don't forget miscarriages as they occur more frequently in people with balanced translocation Explain Chromosomes and Genes (using sample karyotype) When the lab looked at _____ 's cells under a microscope they found a change in the chromosomes The change they found was called a translocation What is a translocation? Transfer of chromosomal material between chromosomes Why do translocations happen? We do not really know why - (Sort of. It happens because it is possible. And its possible because of the inherent nature of the genetic material.) Estimated that about 1 person in 500 has a chromosome translocation We know that our chromosomes seem to break and rejoin quite often, and it is only sometimes that it leads to problems These changes are out of our control, and nearly always translocations happen in either the egg or sperm cell before they join together Therefore they are not likely to be caused by anything during the pregnancy How Translocations Occur Sometimes the chromosomes break during cell division and are usually repaired Sometimes two fragments may break off from two different chromosomes, and "swap" places This is called a reciprocal translocation (this is the type of translocation he has) Show Karyotype and Explain Specific Break Points Sometimes helps to see the actual karyotype 46 means that the usual number of chromosomes is present Y chromosome is what makes him male T stands for translocation, where a piece of chromosome 2 and 21 exchanged places The rest just tells us more exactly where the chromosomes broke So arrows are pointing to where the chromosomal material exchanged places Balanced Translocations In most cases, there is no loss or gain of chromosomal material during the exchange process When the lab looked they didn't see any missing or extra pieces of chromosomes and they therefore think that this might be a balanced translocation What Are the Effects Often people will have a balanced translocation and not even know because they don't experience any problems (this occurs in majority of cases of new balanced rearrangements Warburton 1991) Sometimes, apparently balanced translocation carriers show some characteristics or symptoms (Warburton showed that frequency of abnormality was 6.1% but confidence interval includes 3% in apparently balanced translocations) One explanation for this finding is that the break may have occurred in the middle of a gene that is important in growth or development and the gene no longer provides correct instructions because it is disrupted We do not know if this translocation is the explanation for the characteristics and health problems in ______ What will results from parental chromosomes tell us In order to determine what the translocation might mean it is important to do chromosomes on all parents of children with a translocation If a parent has the same translocation and they do not have any of the same symptoms or characteristics as the child then we cannot conclude that the translocation is the cause If neither parent has the translocation than it may explain some or all of the characteristics and health problems in ______, but would be difficult to know for certain Parental chromosomes will also be important because it will help us determine what risks might be to future offspring What can happen in offspring of people with balanced translocation If one of the parents carries a balanced translocation, it is possible for a child of theirs to acquire a bit of extra chromosome material or a bit missing Either of these would be known as an UNBALANCED translocation This extra and or missing pieces of chromosome can unfortunately cause serious mental, physical and medical challenges in the child who inherits them Sometimes they cause a miscarriage, but not always However, it is also possible for these same parents to have a child with normal chromosomes, or a child with the same balanced rearrangement of their chromosomes as the parent Having a balanced translocation of your chromosomes does not mean you cannot have normal healthy children Factors that influence risks (not applicable in this case) Ascertainment - A family ascertained as a result of a previously affected child is seen to be at increased risk of recurrence since the imbalance has been proved viable. Risk of having an affected child is lower when a family is ascertained following for example repeated spontaneous miscarriage since in these cases the imbalance is more likely to be inviable Each time they have a child, there are several possibilities. they may have a child with normal chromosomes they may have a child with the same balanced rearrangement of the chromosomes as the parent they may have a child with an unbalanced rearrangement of the chromosomes which may cause mental and physical challenges the pregnancy may end in a miscarriage What sort of problems do unbalanced translocations cause? Can be difficult to predict because it depends on: Which parts of chromosomes are missing or duplicated (aneuploidy for 4p, distal 4q and 9p for example all have a high degree of viability therefore relatively high risk) how large of pieces they are (if large less likely to be viable due to more extra or missing information) There are not usually the same breaking points for each translocation because it is random so we don't have any other children to compare this exact translocation to Nearly always have learning problems though if translocation is unbalanced Tests in Pregnancy for Translocation Carriers amniocentesis This is usually done from 14 weeks in the pregnancy and the result normally takes about 2 weeks. Chorionic villus sampling (CVS) usually done between 10-12 weeks in the pregnancy, and the results take about 2 weeks. Psychosocial Considerations Information can be difficult to understand because translocations are not an easy concept Don't expect them to remember everything, we will provide a summary in a letter we will write People who have a balanced translocation of their chromosomes do not have a disease that can be "caught" by other people Guilt about possibly passing this on (not under our control can't cause or prevent) What do other family members know and do you plan on telling them Either parent considering having more children because this may alter their plans or could be upsetting to think they may have a recurrence risk if they didn't think so before References and Patient Resources patient literature about translocations Chromosome deletion outreach support site Unique a UK rare chromosome disorder support group (similar to chromosome deletion outreach) information on translocations more advanced Dorothy