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Friday, December 6, 2013
Inherited Disorders and Birth Defects
Balanced Translocation 10:18
Hello, I am a 27 year old female and have a balanced translocation between Chromosomes(10:18) which I found out after 2 miscarriages at 11 and 5 wks and a MTOP at 20wks, when my baby boy was diagnosed with heart and brain abnormalities at the 20 wk scan. 2 years later I got pregnant with a new partner, and I saw the heart beat at 7 weeks and was ecstatic, but unfortunately I started bleeding at 11 weeks and an u/s showed the baby had stopped growing and no heartbeat. I am now pregnant for a 5th time (5wks) and I am terrified that my BT will cause another pregnancy loss. I know that because of my poor pregnancy history I am a prime candidate for a CVS and amniocentesis, but I am concerned that this may cause another m/c. Could you tell be if you have ever heard of this particular BT (10:18) or how common it is? What are my chances are of having a healthy baby? And what are the risks of miscarriage with CVS or amniocentesis, I know this is probably the least of my worries, but I am desperate for this baby to be OK. My family are yet to get tested for BT`s, but my mum had 6 miscarriages before she went on to have 4 healthy children.
Any answers would be much appreciated.
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 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.
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 10 and 18 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.
You are correct; there is a chance of complications that can lead to a miscarriage following an amniocentesis or CVS. For amniocentesis, doctors usually say the risk is about a half of a percent (0.5% or 1 in 200), but a recent study suggests that the risk of miscarriage may be less than this, about 0.06% or 1 in 1600 pregnancies. For CVS, the risk is higher, about 0.5% to 2%). In any case, it is your decision as to whether or not to have an amniocentesis or CVS.
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