I have a balanced translocation of two of my chromosomes. Never heard of that before? I hadn’t either, prior to the testing we did following our second miscarriage. Essentially a balanced translocation (BT) means parts of two of my chromosomes (#1 and #5) are in the wrong place.
As you may remember from your high school biology class, a typical human being has 23 sets of chromosomes – one inherited from each parent. Like other people, I have 23 sets of chromosomes, but if you examine mine closely, you’ll see that instead of having two complete #1s and two complete #5s, I have one #1, one #5, and two chromosomes that are partly #1 and partly #5. There is a diagram on the top of this page that helps describe the situation. I’m not sure of the original source of that document, but it is posted on the home page of a Yahoo! group for balanced translocations that I have joined and found to be incredibly helpful. I hope it’s okay that I linked to it here.
A person with a balanced translocation is a truly normal person. I have no defects (so they tell me) because I have all of my genetic material. Nothing is missing; some of it is just in the wrong place. (Birth defects occur when there is too much or too little genetic material.) The only problem people with BTs have is related to fertility. In conception, the chromosomes from the egg join with the chromosomes from the sperm, and the 23 pairs of chromosomes are created in the embryo. However, with me, some of my eggs carry the combined chromosomes, and that means that sometimes either too much or too little of the genetic material is there.
In general, there are four most likely possible outcomes (see the left side of this page ) at any given egg+sperm combination for people with a BT. (Technically, there are more, but they involve a great level of technicality, and I prefer to think of it this way – and so does my genetic counselor).
1. Normal #1 and normal #5
2. Abnormal #1 and abnormal #5
3. Normal #1 and abnormal #5
4. Abnormal #1 and normal #5
Of the possibilities above, #1 and #2 both lead to a normal embryo, because both involve the right amounts of genetic material. In #2, the result would be a baby like me, with a balanced translocation. Possiblities #3 and #4 are the problematic ones, because it means too much or too little material is involved. In #3, for example, there would be too much #1 and not enough #5. If a pregnancy were to result here, it would either end in miscarriage (most likely scenario), or it would result in a child with birth defects.
We met with a genetic counselor shortly after receiving the diagnosis, and she gave us some interesting statistics. She said that while a “normal” couple would have a 10-15% chance of miscarriage, our chance is more like 25-30%. And, while a “normal” couple has a 3% chance of birth defects in any given pregnancy, ours is 3-5%. Apparently genetics experts keep data on these things, and she could only find one documented case of a child with my affected parts of these chromosomes surviving to birth. This means that the odds are overwhelmingly in our favor that we would not have a child with birth defects, because a pregnancy with that chromosomal make-up would most likely end in miscarriage. Of course, there is never a guarantee. There is testing that can be done in pregnancy to look for these abnormalities, and we have decided that we would have that testing done when the time comes so that we could be informed and prepared. The statistics we were given are actually better than what we had expected, and we don’t feel like this is an end-all for us. We’ll keep trying, at least for now. We’re not interested in being on this baby-making journey forever. It’s way too difficult and emotionally challenging.
There are high-tech procedures available as well, such as IVF with PGD (preimplantation genetic diagnosis), where the embryos are tested for chromosomal abnormalities prior to implantation. We have decided that this is not the best option for us – for us it is too time consuming, invasive, expensive, and even more emotionally charged, and in the end you still have no guarantee of a child (the odds I have seen are 30-40%). I cannot imagine the devastation we would feel if we spent months going through procedures, daily shots, invasive ultrasounds, minor surgical procedures, and also shelled out $20,000+ if we got another negative pregnancy test. As I said, it’s not for us, but we fully respect those who choose this route. It’s just not for us.