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Inherited Disorders and Birth Defects

Balanced Translocation chromosome 1 and 2

05/30/2008

Question:

I am 35 years old and had a CVS done at 11 weeks. My genetic counselor told me that everything is normal except that my baby has a balanced translocation on chromosomes 1 and 2. My husband and I have been tested and we are not carriers. We were wondering what are the risks of having a child with this kind of BT?Is there any way to figure out for sure if any genes were affected? Is there any way to know what genes chromosome 1 and chromosome 2 deal with?

Answer:

As you know from your discussion with the genetic counselor, 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 would not be expected to have any health problems since all the chromosomal material needed is present and functioning properly.

As you mention, since both you and your husband do not have the balanced translocation, the translocation occurred during conception of your pregnancy. In these cases, most cytogenetic laboratories look very carefully to see if they can identify even a very small problem at the places where the chromosomes broke and switched places. However, the current standard technology may not be able to identify a submicroscopic deletion (missing) or duplication (addition) of chromosomal material. While it is very unlikely that there would be any problems, we cannot say for sure that there might be a problem present.

It may be possible for the cytogenetic laboratory to also look to see what genes are known to be located at the places that the switch took place on chromosomes 1 and 2. If those genes have been specifically identified as causing disease and the technology exits to look at them, the lab may be able to do those analyses.

Finally, there is a newer technology called array-CGH which can detect very small DNA imbalances, however, it may not be available locally. Again, while this technology appears to be very promising, it still will not guarantee that the pregnancy will be normal.

I would recommend that you discuss these questions with the genetic counselor.

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Response by:

Anne   Matthews, RN, PhD Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University