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.