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Friday, July 25, 2014
Inherited Disorders and Birth Defects
Translocation between chromosome 7 and 10
I was diagnosed with having a balanced translocation between chromosome 7 and 10 after we lost our baby at 26 weeks due to multiple abnormalities. She is now 12 weeks pregnant and a cvs has been performed. There`s suspicion of facial cleft and a midline brain abnormality. What if any chace do we have for a healthy child? And what chances do I have of fatherhood?
As you know, 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 since all the chromosomal material needed is present and functioning properly. This is called a balanced translocation.
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 birth defects and cognitive problems such as mental retardation. This is an unbalanced translocation and seems to be the case for your pregnancies.
The chance of having an egg or sperm that has the unbalanced translocation vs. the normal or balanced rearrangement depends on how the chromosomes line up, divide and segregate - that is how the chromosomes divide into two daughter cells. 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. Usually the eggs or sperm that produce an unbalanced complement are miscarried because they are not viable (capable of producing a live born child). So theoretically, there is a 50% chance that the pregnancy would not have an unbalanced rearrangement. If this is the case, you are back to the general population chance of having a healthy baby - about 95-97%.
Unfortunately, researchers do not know why some people who are carriers of balanced chromosome rearrangements miscarry more frequently than other people with the same chromosomal rearrangement. Translocations involving chromosomes 7 and 10 have been described, however, I do not know if your specific translocation (you need to know exactly where on the chromosomes the exchange took place) has been described. Also, there are other reasons for birth defects, so it would be important to know if your baby's abnormalities are due to having an unbalanced translocation.
If you have not already done so, I would recommend that you ask your doctor about a referral to talk to a genetic counselor or geneticist to discuss these issues in depth with you. This is an area that they have a lot of expertise. You can locate a genetics center near you through the National Society of Genetic Counselors Resource Center website below.
Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University