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
 * 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 Translactions 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 than 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 inbalance 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
 * UK chromosome support website (similar to chromosome deletion outreach)
 * information on translocations more advanced
 * Dorothy Warburton. De Novo Balanced Chromosome Rearrangements and extra Marker chromosomes Identified at Prenatal Diagnosis: Clinical Significance and Distribution of Breakpoints. Am J. Hum Genetics 49:995-1013, 1991.