Handbook of Genetic Counseling/Reciprocal Translocation

Reciprocal Translocation Contracting What were you told about why you were referred to Genetics? What did they tell you about the results of the chromosome studies? What are your main concerns? Do you have any questions? Overview of session Intake Follow intake questions What doctors are they seeing? Has she had any surgeries, or is she scheduled for any? What have they been told about the Dandy-Walker malformation and hydrocephalus? What have they been told about her heart defect? Has anyone talked with them about what to expect in the future? Updates to family history? Ask again about mental retardation, learning problems, birth defects Ask again about miscarriages and stillbirths in family Genes and Chromosomes Chromosomes are instruction books for bodies - genes located all along chromosomes One copy of each from mother, one from father Explanation of Chromosomes Show her karyotype to parents and point out rearrangement This is what we call a reciprocal translocation Parts of two different chromosomes break off and redistributed to different chromosomes Her chromosomes look a little bit different than what we would expect This happens to about 1 in 500 people We don't know why this happens sometimes This is not something that we can change or fix Nothing that anyone did or didn't do caused this to happen - it is a random event What Does this Mean We don't really know right now - but there are some ways that we can try to find out It looks like the translocation is balanced All of the genetic material is still there, it is just rearranged (show yellow and pink chromosomes) Most of the time, this does not cause a problem so it would not explain why was born with Dandy-Walker malformation and a heart problem Remember that there are genes along the length of the chromosomes? There are spaces between those genes If the chromosomes broke in those spaces, it should not have disrupted any genes and all of the body functions should still work We would expect a child with a balanced reciprocal translocation to be healthy This would mean that her health complications are caused by something other than the translocation BUT . . . If one or both of the chromosomes broke in the middle of a gene, or if a small piece of one of the chromosomes is missing, that could cause problems (5%) Unfortunately, we can't look any closer at her chromosomes right now, so we can't tell if this is the case If a gene is interrupted or a piece is missing, this COULD explain her problems To help us determine whether the translocation is balanced or not, we need to look at BOTH of her parents chromosomes Importance of Looking at Parent's Chromosomes If you both have normal chromosomes: The balanced translocation is something new If might explain the Dandy-Walker malformation and heart defect If one of you has the same balanced translocation as_____ We know that you both do NOT have Dandy-Walker malformation or a heart defect Because you both don't have any health complications, we know that all of the genetic information is there - nothing is missing or interrupted This means that her problems may have another cause What Does this Mean for her's Future? At this point, it is hard to say Once we know more about parents chromosomes, we will have a better idea about what caused the Dandy-Walker malformation and heart defect If the translocation does appear to be the cause of the problems, we still may not be able to predict what will happen to her in the future As mentioned before, we can't always look close enough at the chromosomes to know exactly what genes might not be working right We can be sure that her gets the care that she needs, including tests to rule out any possible problems and physical, occupational, speech therapies if needed If the translocation is not the cause of the problems, we may be able to identify another cause Either way, the important thing is that her gets the medical care that she needs Reproductive Risks of a Balanced Reciprocal Translocation As we have already talked about, a balanced reciprocal translocation usually does not cause any physical differences Does have impact on reproduction Four possible outcomes for any pregnancy: A child with normal chromosomes Would expect child to be healthy They cannot pass on the translocation to their children A child that is a balanced translocation carrier If the parents are healthy, we would expect the child to be too Child would have same four possible outcomes for a pregnancy as we are discussing now A child with an unbalanced translocation causing a physical or mental handicap Unbalanced translocation means that there is extra or missing chromosomal material Could lead to physical differences, medical problems like heart defects, etc. An unbalanced translocation that leads to miscarriage or stillbirth Usually if the piece that is extra or missing is large (contains a lot of chromosomal material) There are too many changes in genetic material to allow a conception to grow Some people with balanced translocations have problems with infertility Risk Assessment The exact risk assessment depends on where the chromosome breaks Overall, there is 5-30% risk to have child born with physical or mental handicaps (general population is 3-5%) There is a 20-30% risk for miscarriage (general population 15%) Reproductive Options for Balanced Translocation Carrier Just be aware of risks Prenatal testing - amniocentesis or CVS Adoption Sperm or egg donor PGD or IVF Psychosocial How do you feel about what we talked about? Do you have any new concerns? Give patient literature about translocations Feelings of guilt or blame if either parent is translocation carrier Frustration over inability to offer an explanation right now Fear, worry, anxiety about the future References Blough, R. "Chromosome Abnormalities." Introduction to Genetic Counseling Lecture (2002) Buchholz, J. "Genetic Counseling for Autosomal Reciprocal Translocations." Topics in Medical Genetics Lecture (2002). Gardner and Sutherland. Chromosome Abnormalities and Genetic Counseling (2000). Notes The information in this outline was last updated in Sept 2002.