Handbook of Genetic Counseling/Reciprocal Translocation

Reciprocal Translocation

Contracting edit

  • 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 edit

  • 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 edit

  • Chromosomes are instruction books for bodies - genes located all along chromosomes
  • One copy of each from mother, one from father

Explanation of Chromosomes edit

  • 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 edit

  • 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 edit

  • 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? edit

  • 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 edit

  • 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 edit

  • 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 edit

  • Just be aware of risks
  • Prenatal testing - amniocentesis or CVS
  • Adoption
  • Sperm or egg donor
  • PGD or IVF

Psychosocial edit

  • 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 edit

  • 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 edit

The information in this outline was last updated in Sept 2002.