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Cystic Fibrosis: Part 2


So, if we have carrier parents, what are the chances that they would have a baby with cystic fibrosis? If they’re both carriers, it’s one out of four. Yeah. One out of four, exactly. So one out of four, 25 percent. But what are your chances of being a carrier and carrier rates depend upon ethnicity. They depend upon your big family history and you’re overall genetic background. So the highest rate, as I mentioned in the beginning, are in people of northern European descent. So people who came from England, Scotland, Wales, Scandinavia, things like that … that’s my family history. Right? Or, if you’re Ashkenazi Jewish and that’s eastern European … Jewish descent. You’d probably know if you’re Ashkenazi Jewish. So we’re at the highest risk of being a carrier, and for us that’s again my family history … our chances of being a carrier is one in twenty-nine. Okay so about one out of thirty. So if it turns out that you had two parents that are both Caucasian, and we both have that one in twenty-nine carrier rate, then our chances of having a baby with cystic fibrosis is one in 3000. Same for the Ashkenazi Jewish population. So if you look here at this table and if we had two Hispanic parents, they’re carrier rates … one out of 46 and they’re chances of having a baby is one out of about 9000, or less. And you can see the African American risk is even lower at one in 15,000. And the Asian American carrier rate risk is the lowest at one in 90.

So, that’s how it basically works from an ethnic perspective. It’s all about your family history. So … did you have a question? Well, how about if the parents are from different ethnic groups you know Asian, Hispanic or something? Yeah. Perfect. So you would basically take the carrier rate from, let’s say, Hispanic and Asian. If you would take the carrier rate of a Hispanic person, that’s one in 46. And the carrier rate from an Asian person, one in 90. So the risk falls between the two and if you look at the real numbers, it’s actually closer to the lowest risk. Okay? So it tends to come to the lowest risk. Good. Makes sense?

There’s one more affected ethnicity I should tell you about and it has to do with how good the test is. Because it turns out that we have found now about 200 mutations in the cystic fibrosis gene…so 200 different ones. And some of them, we’ve only found in like one or two people. Others we found in most people who have cystic fibrosis. So there’s a common genetic defect that’s the most common one. And when we test, we really test for the most common 30 to 40 to 50 depending on the individual test. And so you don’t test all of them. The ones we test are the ones that are the most common. So if you’re from a higher risk ethnic group, we’re also likely to test for the mutation that you might carry. If you’re from a lower risk ethnic group, we might not even test for the mutation that you could carry. So the test is good in detecting cystic fibrosis carriers in people at higher risk but not so good in people at lower risk. Okay.

So how would you find out if you’re a carrier? We do a blood test. So if you chose to be screened for cystic fibrosis, basically we ask you to sign a little consent form and then we send you off to the lab. And the lab will draw your blood and test those most common mutations to see if you’re at risk and find out if you’re a carrier. So in the ideal circumstances, the result would come back and say no, no mutations identified, right? So that you’re not a carrier of the ones that were tested. So, does that mean it completely excludes the possibility that you could have a baby with cystic fibrosis? No, because there’s some that we still didn’t test. Does that make sense? But it could lower your risk. So generally, though, this is a test that we do on mom specifically. So if you’ve ever had a baby or ever were screened, you don’t need to be screened again for each baby. Like the other tests, they are baby specific. This is a mom specific test. Does that make sense? Okay.

So again, what if we find no mutation? Then we’re done testing. Unless there was a new dad and we found out the dad was a carrier already or had a high or strong family history, and then it might be worth testing. So if you were to take somebody who was tested and, like I said before, if we test you and we found out that there was no mutation, that doesn’t completely exclude the possibility that you could be a carrier. So as an example, let’s say a northern European Caucasian woman was tested and the result came back and said no mutations. So what that does is lower her chances of being a carrier. It doesn’t make it zero but it does lower it a lot. So it goes from, in that case, the one in 29 carrier rate all the way down to about 1 in a 140. And that’s less than the Asian risk of being a carrier, so that woman’s chances then of actually having a baby with cystic fibrosis are very small, even though they’re not zero. Okay. So that’s the ideal circumstances if you chose to be tested, that it would come back showing no mutation.

Well, obviously it could come back showing a mutation. So what do you do if the mom found out that she was a carrier? What do you think? Test the dad. Yeah, you’ve got to find out if dad’s a carrier because it would take dad and mom being carriers for the baby to have a chance to have cystic fibrosis. So, if we found out that both the mom and dad were carriers, then what? What’s the risk? Do you remember that? Back to that previous example. 25 percent. One in four. Yeah, one in four or 25 percent.

So how would you find out. Is there anything else that we could do to see if the baby has cystic fibrosis? Well, we could look with ultrasound and there are some things that are suspicious sometimes, but not always. So, how would you know before a baby was born if a baby had cystic fibrosis? You have to test them. You have to test them directly. So how would you test a baby directly? The amniocentesis? Yeah, it goes back to an amnio. Right? All the way back to that. That’s the only way you’d know for sure before the baby’s born if the baby was a carrier, if you were testing that or if the baby actually had cystic fibrosis. Okay.

Now of course if you found out that you were a carrier and the dad was a carrier you … you don’t have to have an amnio. You could wait until after the baby is born and test the baby then. Okay.

Now, interestingly enough, guess whose baby’s are getting tested after they’re born? It’s state-by-state dependent, but a lot of states now are doing, automatically, cystic fibrosis screening on babies right after they’re born. So after they’re delivered, they’ll prick the baby’s heel and take a few drops of blood and put it on a little card and one of the things that they do in many states is screen for cystic fibrosis, among other metabolic situations. So if you knew the baby was at high risk, you would actually test the genes directly.

So we’ve talked about already what are the potential benefits of knowing before the baby’s born, and they have to do with preparation and knowledge, and then the issue about whether or not to continue. Now I should say this about cystic fibrosis. I mentioned, just as a reminder, we’re getting better and better at treating it. And there’s even a possibility, since we know the mutation, that we might be able to do some genetic manipulation in the future and fix it. But we’re not there yet. But we’re getting better and better at treating it. So some children, you can even know the mutation and it doesn’t always predict how severely affected someone would be. So, it’s variable in their clinical outcome and so forth.

All right back to the same question, should you get testing? It’s up to you. Right? Just like most of the stuff that we’ve been talking about today, the test is of greatest value to people who are at the highest risk. So people who are northern European descent or Ashkenazi Jewish … those are the people that it makes the most sense to test. And likewise, testing is less effective or less useful for people of ethnic backgrounds that are of lower risk such as African Americans, Asian Americans, and Hispanic Americans.

All right, so a couple of reminders. Before I do, let me make sure you guys don’t have any questions. Any questions? I have a question. Yeah, sure. So if someone has an amniocentesis, are they automatically tested for cystic fibrosis as well? Ah yes, good question. No is the answer to the question. So yeah, if we did an amnio for … if we saw an abnormality and we were concerned about a chromosome problem then we would do the amnio and test for the chromosome problem. And, in fact, I was kind of going there in the next set of slides. But we really don’t test for all genetic conditions when we do an amnio because all genetic tests are really specific, like each one is an individual test. So for example, if we tested for cystic fibrosis and said there’s no mutation in the cystic fibrosis gene, that doesn’t mean that we’re saying that you don’t have any other genetic abnormality. And unless we’re specifically going after that issue, we don’t necessarily test that if we’re doing an amniocentesis, okay? So, we’ve finally gotten to the point where we’ve actually sequenced our whole collection of genes, our whole genome, but we haven’t gotten to the point where we really can do that cost effectively, or do that for everybody all the time. So there’s no good genetic test for everything.

Now, if you do have a family history of a specific condition and we need to know about that you should sit down and speak with one of us, a maternal fetal medicine doctor or a genetics counselor. And we can talk to you about your specific genetic situation and we may recommend certain testing in that case.

So, as we wrap up here about cystic fibrosis, let me make just a couple other comments about genetic testing. Okay and having your genes tested. Anybody see the movie Gattaca? Yeah. Yeah. An outer space movie, yeah. It’s futuristic. It’s a story about … it’s an interesting story. This one guy is born and he was a spontaneously conceived, unplanned pregnancy, and so there wasn’t any specific genetic selection in him but he’s got a brother that was selected to be very successful, and so forth. Well, this guy who doesn’t have the ideal genetic situation is supposed to be at high risk for having heart disease. And so, when he wants to be an astronaut, they won’t let him be an astronaut because they know that his genetic future puts him at high risk for heart disease. So it’s sort of a crazy concept, but do we really want people knowing all of our genes, and our “at risks,” and so forth? You know there are some potential risks or complications with that. So you should know that now, as a researcher, I often want to do genetic testing for specific things but you should just be a little cautious when you have your genes out there to be tested. That’s what that movie reminds me of.

And related to that is the issue of insurance. Now, in the military we have an insurance system that we already have by virtue of being a part of the military. But can you imagine that if you were trying to get insurance some time, they ask you questions, right? They ask you about your health. They ask you about things like tobacco. Why do they care about tobacco use? It can affect your health. Right. Right. So, do you think an insurance company would be really excited about taking care of somebody who is a cystic fibrosis carrier? Probably not. I mean the carrier would be fine but then they say, “What about your children?” Right? And you might say, “Well I’m a carrier but my husband’s not.” So this is sort of a paternity test. So that’s the other thing to know about when you go do genetic testing. Okay. So, just a couple of things to have in mind.

Now, I already mentioned that the pediatricians are testing a lot of babies now in many states now. Babies are getting tested so that may weigh into your decision about whether or not you want to be tested prenatally. Okay.