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Sunday, May 26, 2013
Inherited Disorders and Birth Defects
Balanced translocation and breakpoints?
My husband carries a balanced translocation at 5p13 and 12q22. I understand that typically, the larger the breakpoints the less likely an unbalanced pregnancy would survive to term. My question is, are these large breaks? And would we most likely miscarry early with an unbalanced pregnancy?
Your understanding is correct. 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, just rearranged - that is, switched places (translocated) - this person should have no health problems since all the chromosomal material needed is present and functioning properly - such as the case for your husband.
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 most often miscarry, however in some cases, can lead to birth defects and cognitive problems such as mental retardation in a liveborn infant. This is an unbalanced translocation.
In your husband's situation, having a translocation between chromosome 5 and 12 with those break points - could result in a pregnancy with a normal 5 and 12; a pregnancy with the same type of balanced translocation as your husband (this child would be expected to be normal) or pregnancies with either having an extra copy of 5p and missing a copy of 12q or having an extra copy of 12q and missing a copy of 5p.
I looked at the research literature to see if children with an extra copy of 5p or 12q have been identified by other geneticists, as well as children with only one copy of 5p or only one copy of 12q. There have been reports of children with an extra copy of the same (or similar) segment of 5p that is in your husband's translocation. But there are no reports of children being born with only one copy of the 12q segment that is in your husband's translocation.
As for the other unbalanced possibility - having only one copy of 5p and an extra copy of 12q - there have been children reported in the literature with these , which suggests that these pregnancies with this unbalanced form of your husband's translocation may have a greater risk of surviving to term.
If you have not talked to a geneticist or genetic counselor, I would highly recommend that you do so. They would be able to discuss your questions in detail as well as to discuss possible options regarding pregnancy. You can locate a genetics center near you at the National Society of Genetic Counselors' Resource website listed below.
Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University