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Inherited Disorders and Birth Defects

Translocation of chromosomes 1 & 4

09/11/2008

Question:

We have had 4 misscarriages, the last of which was through ivf. The longest pregnancy duration was 9.5 weeks. I (husband) have been diagnosed as having chromosome translocation of 1 & 4 chromosomes. To which point (%-wise) are these miscarriages attributed to this fact? My wife`s womb is of heavy adenomyosis nature. How can one treat or bypass the problem of chromosome translocation in order to elliminate this factor in case it is responsible of the misscarriages? Thank you very much.

Answer:

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 diagnosed in you - a rearrangement between chromosomes 1 and 4) - 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 gametes (eggs or sperm) that the mom or dad produces - will have a normal chromosome complement, 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 # 1 and chromosome # 4. In all of these cases that produce an unbalanced complement - there is a very high probability (greater than 99%) that the pregnancy will miscarry. However, depending on where the switch between the chromosomes happened, there could be a small chance that a pregnancy with an unbalanced translocation would continue. In this case, the baby would most likely have multiple birth defects.

If a parent has a balanced translocation, while they are at risk to miscarry somewhat more frequently than people who do not have a chromosomal translocation, they can have healthy pregnancies. However, the chance or percent of having a miscarriage if someone has a translocation can vary a great deal and depends on the specific type of rearrangement involved. There is nothing you can do to change the translocation as it is in all the cells in your body. However, there is a procedure called Preimplantation Genetic Diagnosis (PGD) that uses IVF technologies to fertilize an egg with a sperm that does not have the translocation.

You ask excellent questions. If you haven't 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 chromosome rearrangement. They can also discuss PGD with you as well. 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

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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