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Inherited Disorders and Birth Defects

Balanced Translocation in Chromosomes 3 &15

03/04/2010

Question:

My husband has a Balanced Translocation of the Chromosomes #3 and #15. We had our son tested and he tested negative for a Balanced Translocation and Unbalanced translocation. My son has the dysmorphic looks, Autism, mild retardation, ears that stick out, which I hear are common with a Balanced Translocation. When we walked into the Dr`s office two years ago the Dr. immediately asked if he had a Balanced Translocation. I was floored and asked why he asked and he said because he had the physical looks. But again he tested negative for a Balanced and Unbalanced Translocation. And most recently he was tested for any DNA rearrangement and it all came back normal. My son`s Dr. feels that my son`s father`s chromosome problems are most likely caused due to his father having the Balanced Translocation. Can you tell me what the odds are of having another child with these problems or what are the odds of having another child with problems? What are the odd of having a child with no problems. Do you feel this would be some relation to the Balanced Translocation? I have read the Men with translocations are more likely to produce children on Developmental Disabilities, but woman with the disorder don`t seem to have the same issues. That they seem to only pass on the translocation and no other problems noted.

Is this true?

It seems to me that a lot of people who have Balanced Translocation produce children with developmental issues, but I don`t see much info on this. Why is that?

Answer:

You ask some excellent questions. As you probably know, chromosome translocations 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) - it is called a balanced translocation. The person with a balanced chromosomal translocation should have no health problems since all the chromosomal material needed is present and functioning properly. There is no way to tell whether or not a person has one of these balanced rearrangements unless you look at his or her blood (or other tissue) to examine the chromosomes.

However, 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 birth defects and cognitive problems such as mental retardation. This is an unbalanced translocation.

Since your son has had his chromosomes tested and he was found not to have a chromosomal translocation, it is unlikely that your son’s problems are due to a translocation. Moreover, if your husband, who has the balanced translocation between chromosome # 3 and # 15 has no problems, and the cytogeneticists have determined that your son did not inherit the translocation from his dad, then his problems with autism, mild mental retardation and dysmorphic features may be due to another genetic problem or syndrome that is not at all related to a chromosomal translocation.

You mention that your son also had DNA testing that did not show any abnormalities either. However, depending on the number of genes that were examined in the DNA testing that was done – sometimes DNA testing only looks for changes (mutations) in a few specific genes, sometimes the testing may look for changes in many genes (DNA testing does not look at all our genes) and sometimes DNA testing cannot find the mutation (change) in a gene that is looked. So there are children that have the types of problems that your son has in which no specific change (mutation) in the DNA is found. Unfortunately, even with new technologies, there is still a chance that no genetic diagnosis is found.

At this time, since you do not know what the specific cause is for your son’s problems, we cannot tell you what the chance is for this to happen again in future children. However, because your husband does have a balanced chromosomal translocation, there is a chance that you could have children that have an unbalanced translocation which could lead to birth defects and/or mental retardation. Theoretically, there is a 50% chance that someone with a balanced translocation can have a child with an unbalanced translocation. However, in reality, the chance of this happening is much smaller. More often, if the is an unbalanced translocation, the pregnancy often ends in a miscarriage.

If you have not already done so, I would highly recommend that you speak to a geneticist or genetic counselor to discuss these important issues. They have the expertise to explain all of the testing in depth and provide you with the most accurate information. You can locate a genetics center near you at the National Society of Genetic Counselors’ Resource Center website give below.

Related Resources:

Find a Genetic Counselor - National Society of Genetic Counselors

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