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Inherited Disorders and Birth Defects

Balanced Translocated Chromosomes 3,9

06/02/2009

Question:

My girlfriend has a balanced translocated chromosomes 3,9. She has had two successive miscarriages. We are trying to have a child, what are the chances of having a normal pregnancy and healthy child?

Answer:

As you probably know, a translocation occurs when two pieces of chromosomes break off and switch places with each other.  If all the chromosomal material is present, just rearranged (such as the translocation that has been found in your girlfriend - a rearrangement between chromosomes 3 and 9) – this person is called a balanced translocation carrier and should have no health problems since all the chromosomal material needed is present and functioning properly. 

However, when a person with a balanced chromosomal rearrangement forms eggs or sperm, some of the chromosomal material can be lost or duplicated so that the developing embryo has too much or not enough genetic material.  This is what leads to an unbalanced translocation and usually a miscarriage. 

In theory, there is a 25% chance that the eggs or sperm that mom or dad produces – will have a normal chromosome count, a 25% chance that the egg or sperm will have the balanced translocation and a 50% chance that the egg or sperm would produce an unbalanced chromosome complement. In your case, the unbalanced complement would be between chromosome # 3 and chromosome # 9.  In all of these cases that produce an unbalanced complement - there is a very high probability (greater than 99%) that the pregnancy will miscarry.  In the very small chance that a pregnancy with an unbalanced translocation did not miscarry, but continued, the baby would most likely have multiple birth defects or problems. 

So theoretically, there is a 50% chance that the pregnancy will have normal chromosomes or a balanced rearrangement.  Thus, if a parent has a balanced translocation such as your girlfriend, while she has an increased chance to have a miscarriage more frequently than people who do not have a chromosomal translocation, she can have healthy pregnancies.  Do not forget,  the chance for any woman who gets pregnant to have a miscarriage  is about 15- 20%.. 

You ask excellent questions.  If you and your girlfriend have not already done so, I would highly recommend that you sit down with a genetic counselor or geneticist and talk about these risk figures specifically in regard to your girlfriend’s chromosome rearrangement.  The National Society of Genetic Counselors resource link can help you locate a genetics center near you.

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