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Thursday, May 23, 2013
Inherited Disorders and Birth Defects
Chromosome Balanced Translocation
Dear Sir or Madam: Good afternoon! I have a question for my older sister. She is pregnant for about seven months and she`s 39 years old. The due date is Sept.8. She had a test on April. 30. Two days before she got the result that doctor told her there are something not good for her baby. It`s 46, XY, t(12;18)(q24.1;q11.2). The doctor said it`s chromosome balanced translocation. Now my sister and her husband are waiting for test result for their own chromosome. All our family don`t know what does that mean the Chromosome balanced Translocation for the baby and how badly will happen to our little boy and what may caused by the disease. Could you please tell us about it. Thank you very much for your time. Best regards
A balanced translocation happens when two pieces of chromosomes break off and switch places with each other.
Chromosomes are the structures found in the cells of our bodies that hold genes. It is the genes that tell our bodies how to form, function and grow. The genes in each cell are located along the chromosomes - 46 in each cell. Chromosomes come in pairs, 23 of the chromosomes come from the mother and the other 23 come from the father.
In the situation you describe, it would mean that part of chromosome 12 and part of chromosome 18 have broken off and switched places. If all the chromosome material is present, just rearranged (translocated) - this person should have no health problems since all the chromosomal material needed is present and functioning properly. This is a balanced translocation.
However, if some of the chromosomal material were to be lost or duplicated when the chromosomes broke and the switch took place - then there would be extra and / or missing information. This usually leads to a miscarriage, but occasionally, children are born with these types of rearrangements and they almost always have problems. They can lead to birth defects and cognitive problems such as mental retardation.
The specific types of problems or birth defects would depend on the specific areas of the chromosomes that were lost or duplicated and what genes are located at these sites. For many unbalanced rearrangements (translocations) it is not possible to predict what abnormalities to expect; for others the medical literature may provide information.
In the situation you describe - if the chromosome rearrangement is balanced - there should be no health problems for the baby. The doctors are also looking to see if the baby inherited the translocation from either your sister or her husband. If either of them does have a balanced translocation, then other family members may want to have testing to see if they also carry the balanced translocation.
I hope that your sister has had the opportunity to talk to a geneticist or genetic counselor to ask these questions. If they have not, they can locate a genetics center near them by going to the NSGC resource center website below. Another useful website is the Chromosome Deletion Outreach. It has a nice explanation of chromosomal rearrangements in their introduction section.
Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University