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Inherited Disorders and Birth Defects

Balanced Translocation (22;11)

08/31/2009

Question:

Good morning, I`m not from USA, so hopefully my English will be sufficient to get the feedback.

I had three miscarriages, in 2007 and 2008, after that the doctors found out I have balanced translocation (22;11). The exact diagnosis is 46, XX, t(11;22) (q24;q12). Both miscarriages occured early (7th and 12th week). Third one was allright untill 17th week, when I had to go to amnio. I had to wait for the results untill week 20th, when I received an info, that my "child" has the same balanced translocation as I have, BUT also trisomy on chromosome 21st, which means Down`s syndrome. So that was my 3rd miscarriage, or better = my own decision.

Is there any explanation for that or was it only coincidence, that my "child" had got good chromosomes (concerning translocation), but get one more on 21st?

My husband has normal karyotype, so that`s an "advantage". My mother is also carrier of the same karyotype as I have, but both me and my brother are healthy and "normal" :)

I read a lot in your topics and frequently asked questions, that it`s not so easy to explain, why someone has more miscarriages than the other one, is there probably any explanation for this Down`s syndrome? Why did it happen in 2009? I`m 30 years old, so also the age is probably not a reason.

Now I`m planning to try it once again, I just do not know, how much power will I need to be pregnant again. Actually I can not look forward to it, I only have to wait untill the week 20th and than decide what to do, if the situation will repeat.

Is there maybe by every specified translocation higher/lower risk to be pregnant and not to loose the child? I mean, some of those chromosomes are really specific and have been already investigated, which specific diseases they are carrying. I was also checking the website www.ncbi.nlm.nih.gov, but as you said before, it`s very technical, so I do not understand all those information.

I was also consulting this with my geneticist, if it`s not better to go to IVF, but she said, that for sure not, I can really have easily a healthy child. Is 25% (or 50%) enough to be "lucky"? My geneticist said to me, that by IVF they will also not find out all of the diseases, so it can happen that they will find the basic ones like Down`s syndrome or similar, but not the unbalanced translocation (which usually leads to miscarriage, but sometimes not)?

Thank you in advance.

Answer:

I am very sorry to hear about all of your miscarriages; it must have been very difficult to have been through 3 pregnancy losses.

As your geneticist may have told you, there should be no association between being a carrier of a balanced translocation such as yours and having a baby with Down syndrome, which is do to an extra chromosome 21. The extra chromosome 21 was due to an accident of the chromosomes in the egg or sperm not dividing correctly, called nondisjunction. We know that this happens more frequently when mothers are older (usually over 35), but do not know why it happens in younger mothers. In younger mothers, if they have a baby with Down syndrome, the chance that they will have another baby with the Down syndrome due to trisomy 21 is low, perhaps about 1%.

It has been reported in a few cases, that a woman has had more than one pregnancy or baby born with Down syndrome due to trisomy 21 or had another trisomy. In these case, researchers believe there may be some theoretical basis for some people to be predisposed to nondisjunction of chromosomes when forming egg cells.

Why someone like yourself, who is a carrier of a balanced translocation between chromosomes 22 and 11 , would also have a pregnancy that had trisomy 21, I do not know.

Preimplantation genetic diagnosis (PGD) is the technique that is used during IVF to look for chromosome abnormalities such as Down syndrome. In the US, centers that do PGD can also look for chromosome rearrangements. But your geneticist is correct; using PGD cannot look for all genetic diseases and cannot guarantee that a baby will be healthy. However, it may be helpful in looking at embryos and choosing to use only those embryos that do not have a chromosome problem.

I wish you all the best.

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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