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What is cystic fibrosis?

Created by Amy Fan.

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Video transcript

- [Voiceover] Cystic fibrosis is one of those names that doesn't really describe what the disease is. I mean, fibrosis, it's a lot of scarring and cysts, we think of fluid-filled sacks and this does come into play in the pancreas as we'll see later. But for now, just think of cystic fibrosis or what we usually just say CF, as just a name for this disease and we'll find out step-by-step what it actually describes. First, cystic fibrosis is a genetic thing, so, it comes from our genes or is encoded in our DNA. I'm trying to draw the double helix of the DNA right now... like that, and we get this, of course, from our parents. Humans have 46 pairs of these. You get one from mom, one from dad, Cystic fibrosis is a recessive disease as opposed to dominant. In very simple terms, recessive and dominant just refer to how many copies of the defective genes you need to have the disease. If we think of the CF gene as having two different variations, for most people, it's a normal gene. Let's use big B, that's normal. Then, for the gene with cystic fibrosis, we have a little b. Remember that the little b carries the mutation for cystic fibrosis You can get one from mom, one from dad. Out of these two, there are three possible combinations. We have big B, small b, that's one. We can have big B, big B or small and small. For recessive diseases, you have to have two copies of the defective gene so mom and dad must give you the CF gene for the disease to happen. This is different from dominant diseases where it only takes one copy of the defective gene. Let's do a quick genetic lesson here. If we have two people having kids and both of them carry the CF gene but they don't have it, remember, you need both copies of the little b to have it so they both have the little b but neither of them has the actual disease and then get together and have kids. There are four different combinations between their two copies of genes. For this square we get big B and big B. Does this person have CF? No, they don't have the CF gene at all. For this person, they carry the copy but just like their parents, because they only have one copy, they don't have the disease. Same with trial number three, but for this last one, you get small b and small b and this child has CF. For this particular combination, it's one and four so you can imagine the math gets a little more complicated, depending on what the parents have. All of this to say that cystic fibrosis is something that's passed on genetically and whether or not a person gets it depending on what their parents have for the CF gene. The studies and the numbers show us that this disease is most common among the Caucasian population just because of the frequency of the small b, the CF gene in this population. Since there's the highest frequency of CF genes within the Caucasian population, traditionally, they have been most affected by this disease. Out of 3,000 people in the Caucasian population, one person would have CF. They would have this little b, little b combination. For other races, traditionally there has been less frequency of the disease because the gene is not as frequent. For example, in African people, there's about 15,000 people who get one person with CF and in Asians, there's about one in 30,000. Now, these numbers of course change all the time but the point is, the more frequent a gene is in a population, then there's more chances of you getting little b, little b. What is actually defective about the CF gene is it's a gene that controls the transport of two little ions. One is chloride and the other one is sodium. This is the chemical symbol for sodium. Chemistry is really interesting because sodium chloride together, that's table salt. That's what we eat, but these molecules are in our bodies. They do different things at different places. The CF gene controls how they behave and this is the thing that's defective. As a result, we get all these problems. It's like if you have a machine made of tiny little cogs of all different shapes and sizes and they're just held together and for the machine to work, every piece should do their job. There's one piece, let's say, this size that just keeps having problems so the same piece is in different parts of the machine with different jobs and when they're defective because genetically, it's defective, then every time you get to the CF gene something is wrong so the symptoms that we see are all over the body. It's not concentrated in one organ. One of most heavily effected organs and also the place where most CF patients have a lot of trouble Is the lungs. You might think, "How does chloride "have to do with the lungs? "Why does it make such a big difference?" The thing is, our lungs are lubricated by all of this mucus and chloride and sodium play a big part in how much mucus, what's the concentration of it, so when they are malfunctioning, then the nature of the secretions change so it is a nice mucus that coats the lungs and let it function normally, we get these thick secretions that clog up the lungs. With that, you get a lot of infections because it's almost impossible for them to clear all that thick mucus out of their lungs. Infections. To make matters worse, that environment they have foster infections that we wouldn't even commonly see. For example, there's something called Pseudomonas. A Pseudomonas infection is very rare in a person without, in a healthy lung basically but in CF patients, it's very prominent and it's harder to treat. Also, it's just hard to take a real good breath with all that gunk in there so the O2 concentration might be low. Since it's hard to cough up all that mucus, you'll see CF patients have to wear this vest for maybe 30 minutes a day that's plugged to a machine that just mechanically shakes out the mucus in their lungs. It's a standard therapy for people with cystic fibrosis. Another big area that is a huge problem with cystic fibrosis is the digestive tract so we in particular have the pancreas and really, just the GI system in general. The pancreas is an organ that's tucked under the diaphragm there and its main job is to secrete all these things to help us digest our food. Same thing with the secretions here so when it's all clogged up, the enzymes are supposed to come out, can come out so especially when these patients are children, it's hard for them to get the nutrients they need to grow so even if they eat a good diet a lot of times they're malnourished because the nutrients don't get absorbed into their system...malnourished. In a similar way, the liver is on the opposite side of the stomach as the pancreas. It secretes bile. All this mucus again in the ducts and the bile can't get out. Bile helps us emulsify the fats that we eat and digest it. The pancreas also gives us insulin. Insulin is the chemical that helps us regulate the blood sugar so with the lack of insulin, a lot of times, these patients have symptomatic diabetes. Definition of diabetes is not being able to control your blood sugar. So, if you don't have insulin, it's like they have type one diabetes. With the malnourishment, the diabetes, the lack of digestive enzymes, kids with CF often have trouble reaching their full stature so their growth is usually restricted. As you can see, one little gene that controls the transport of these two molecules. I'm trying to show you that it goes to the lung, the pancreas, everywhere in the body really and our treatments tend to revolve around how to control the symptoms of these problems. There are symptoms in CF that's not really treated. For example, since sodium and chloride makes salt, oftentimes, their sweat in their skin just tastes more salty, but that's not something that affects people's health so much so that's not treated as much. The point is, cystic fibrosis shows up in so many ways throughout the body and going back to the name, why do we call it cystic fibrosis, this is describing the scarring that occurs in the pancreas as a result of the disease, you have these cysts then you have scarring from all the blockage and the damage to the tissue that leads to. That's why I said cystic fibrosis is not that descriptive of the disease but just remember, it's really a group of symptoms that all happen because of this recessive gene controlling sodium and chloride.