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Video transcript

- [Voiceover] So as of now, we haven't really been able to identify one true cause of Multiple Sclerosis. But we have been able to identify a number of both genetic and environmental factors that may be involved in propagating the disease. So first I kinda wanna talk a little bit about the genetics. So how do we know that there is a genetic component to the disease? Well, we do, what are called, twin studies. So in these twin studies, what we'll do, is we'll take a pair of identical twins, and a pair of fraternal twins, and we'll compare them. So we know that identical twins have the same DNA, and fraternal twins have different DNA. So what we can do, is we can compare the incidence of Multiple Sclerosis in identical twins and in fraternal twins. So let's say one of the identical twins has Multiple Sclerosis, then the likelihood of the other twin having the disease is about 25 to 30 percent. But in fraternal twins, that number is about as low as five to 10 percent. So given the fact that identical twins have the same DNA, and that fraternal twins have different DNA, this tells us that there is a pretty high genetic component in Multiple Sclerosis. But Multiple Sclerosis, as far as genetics is concerned, is actually pretty complicated. It's thought that about over 50 genes are involved. And they're still finding more and more to this day. Now there's actually one gene that I want to talk about, and the reason why is because this gene is involved in autoimmunity, and it's found on Chromosome six. So, here's the chromosome in question, and you'll notice that I've actually highlighted the part here in red. And this part will contain a gene called HLA-DRB1. And you know, this is kind of a lot of letters here, so we'll mostly just focus on this part over here, the HLA part. So what is HLA? Well, it just stands for Human Leukocyte Antigen. So, H-L-A. So, what does this guy do? Well, let's say that you have any general cell over here, on this cell, you're going to have a protein on the surface. And that is going to be our human leukocyte antigen. This human leukocyte antigen will then have some other kind of protein or peptide bounded to it. And that protein or peptide may belong to something like a virus, or bacteria, or something that shouldn't belong. And so what it's gonna do, is it's actually going to present that to another cell, namely, your T cells. So maybe we have a T cell over here. So the T cell is going to look at this peptide that's being presented by the original cell, and it's going to say, "Okay, so this doesn't belong here, "so we need to kind of begin an attack and defend the body." So really, this entire gene is important for allowing the immune system to determine what is part of the body and what isn't part of the body. And it's thought that a malfunction in this gene is implicated in autoimmunity. Now, remember that Multiple Sclerosis is also an autoimmune disease. So, it's thought that when this gene malfunctions, then this could potentially lead to Multiple Sclerosis. So that's some evidence that, you know, genetics may be involved. But now I wanna talk a little bit more about the environment. And there are a lot of different factors. So first what we're going to do is we're actually gonna look at a picture of the earth here. So here, we have the equator. And at the equator is a pretty low incidence of Multiple Sclerosis. And as you move north from the equator, that incidence increases. So why is that, why is there this kind of geographic spread of the disease? Well, at the equator, there's a lot of sunlight. So people who live here will be exposed to a lot of sunlight. When you're exposed to a lot of sunlight, then your skin can actually start to produce vitamin D. So, on average, people who live near the equator will have more vitamin D than people who live further away from the equator. Now why is this important? Well, vitamin D is actually thought to be involved in regulating the immune system. So a lot of immune cells, let's say you have a T cell over here, a lot of these immune cells may have a receptor for vitamin D as well. So maybe you have vitamin D here in red, and it's kind of bound to this receptor of this T cell. And when you have a deficiency in vitamin D, it's thought that this can lead to autoimmunity. So as you move further and further up north, you're exposed to less sunlight. If you're exposed to less sunlight, then you have, you most likely have less vitamin D in you. If you have less vitamin D in you, then this could lead to an autoimmune disorder, namely Multiple Sclerosis. So it's thought that this may be the reason why the incidence of MS increases as you move away from the equator. Another environmental factor is exposure to some kind of virus in your childhood. So what kind of virus are we talking about here? Well, there are a lot of different viruses that may be implicated. So for example, the Epstein-Barr virus, measles, mumps, and even herpes. So it's really important to know that these viruses themselves do not directly cause Multiple Sclerosis. But if you have had exposure to these viruses in the past, then your chances of developing the disease is increased. So why does this happen? Well, it's thought that the proteins in this virus actually resemble some of the proteins that are found in your nervous system. And so this phenomenon is called molecular mimicry. It's when the virus kind of resembles what's in the body, and the immune system actually kind of confuses the two. So the last thing I want to talk about is smoking. Now we all know that smoking is bad for your lungs, but it's also thought that smoking may increase your chances of getting Multiple Sclerosis. So if you look at a group of people who smoke and who have Multiple Sclerosis, if they stop smoking, then the progression of their disease slows down. So why exactly this happens, we're not 100 percent sure. All we know is that there's this correlation between smoking and the development of Multiple Sclerosis. So I've shown you a lot of different risk factors that may be involved in developing Multiple Sclerosis. So here on the genetic side, you have over 50 genes that may be involved, and I've also shown you all these different environmental factors that may be involved as well. But unfortunately, we haven't really been able to connect all these factors together. And because of that, we haven't really been able to identify a single cause for the disease. But as it is right now, these are some of the major risk factors implicated in getting Multiple Sclerosis.