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Inherited Disorders and Birth Defects

Birth Defects From Balanced Translocation

12/22/2008

Question:

Amniocentesis in pregnancy week 16 just revealed a balanced translocation t(5:7) p15.3:q32. We are living in Poland and the geneticist told us there is a 5% chance of serious mental or physical disorders from this abnormality. Is the risk really so high? Other online articles suggest a negligible risk (if the translocation is indeed truly balanced).

Answer:

As you are aware, a balanced translocation occurs when two pieces of chromosomes break off and switch places with each other. If all the chromosomal material is present, but rearranged – that is, switched places (translocated) - this person should have no health problems due to the translocation since all the chromosomal material needed is present and functioning properly.

However, there can be problems if some of the chromosomal material that was switched is lost or duplicated when the chromosomes broke and the switch took place – then there is extra and / or missing information that can lead to miscarriages, birth defects and cognitive problems such as mental retardation. This is an unbalanced translocation.

While there should be no problems if the translocation is balanced, on rare occasions, if the breaks in the chromosomes happen to be in the middle of a gene, it could disrupt normal functioning of that gene or genes. Usually when a fetus is found to have a translocation, the parents have their chromosomes analyzed to see if one of them also is a carrier for the same balanced translocation. If one of the parents has the same translocation, then the risk for problems in the pregnancy is mostly likely very small. However, if neither parent has the translocation, and this is new (de novo) in the fetus, there is a possibility that some of the genetic material was lost or duplicated or genes interrupted, and the risk is increased for birth defects and mental retardation if the pregnancy does not miscarry. The 5% risk for problems that the geneticist gave you is reasonable if neither parent is a balanced translocation carrier.

If you and your spouse have not had your chromosomes done, I would suggest that you speak to the geneticist about having this done.

Related Resources:

National Society of Genetic Counselors Resource Center

For more information:

Go to the Inherited Disorders and Birth Defects health topic, where you can:

Response by:

Anne   Matthews, RN, PhD Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University