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Genetics and Parkinson's disease

Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Emma Giles.

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Video transcript

- [Voiceover] So, in most people, right when we're talking about their Parkinson's Disease we say that their Parkinson's Disease is Idiopathic. And that just means that we don't know what caused it. And that's actually the case for the vast majority of people with Parkinson's Disease. About 85% of people. So that's a lot, right? But in a handful of people with Parkinson's Disease about 15%, we actually do know what caused the disease. And for these people something's actually gone wrong with at least one of their genes. So a quick recap on genes. Remember that genes are essentially specific segments of our DNA, right? So you'd find them in almost every cell in your body. So, there are specific segments of DNA that provide instructions to the cell. And each gene is like a special recipe. So each gene has instructions for how to make different proteins. And once these proteins are made they go off and they do tons of different tasks. Tons of different important tasks all around our bodies. Like, well, basically everything. Basically everything is done by proteins. >From creating our cellular structure to our organs, to our enzymes. Those are proteins too. Essentially every structure or process in our bodies that you can even think of, absolutely everything, somehow involves proteins. So when something goes wrong with our genes, let's say its supposed to look like this, right? but maybe due to a mutation, a change in that gene, it ends up actually looking kinda different. So maybe something like this here. Now all of a sudden the instructions, the recipe that that gene has for making their proteins, they're not correct anymore, right, they're not the same. And so the proteins that should be made, the proteins that we want these genes to make, now they can't be made properly anymore. At least in cells that have these genes that are affected, that are changed, that are mutated. And when proteins aren't made properly well, they won't be able to carry out their normal roles anymore, right? So we actually have a collection of genes, a family of genes, that when they're changed, when they're mutated in some way can either directly cause or increase our chance of developing Parkinson's Disease and this depends on which gene gets mutated. Now remember how we get our DNA, how we get our chromosomes. So we have 23 single chromosomes that we get from our dad and we get another 23 single chromosomes from our mom. And they form pairs so we end up with 23 pairs of chromosomes, right? So that means that we have two copies of each gene. Right? One copy came from your mom and one copy came from your dad. Now let's actually classify genetic causes of Parkinson's Disease into two groups. So two types of inheritance if you will. So we'll say Autosomal Dominant over here. And we'll say Autosomal Recessive over here on this side. And this'll all start to make sense in a minute here. And the inheritance patterns can get really detailed and messy. So I'm not gonna really go into all that at the moment. But basically I wanna get across here that the Autosomal Dominant types of Parkinson's Disease or really any other disease that's inherited in an Autosomal Dominant way, you only really need one bad copy of the gene. So either one bad copy from your mom, or one bad copy from your dad. And that would be enough to cause the disease. So in this case, in our case that's Parkinson's Disease. And Autosomal Recessive, well that means that both mom and dad need to pass on to you a mutated copy of the gene. And there's one other thing I should mention. So when we say that a gene mutation causes a disease. So in this case we say a gene mutation causes Parkinson's Disease, we can either mean that it definitely causes the disease, 100%. So if you get the mutated copy or if it needs two copies of the gene you will definitely develop the disease. Or, we can mean that getting the mutated copy, or copies, will increase your chance of developing the disease. So those two things are a little different, right? And for some genes, certain mutations within that gene will definitely cause the disease and other mutations in that gene may just increase the chance of the disease developing. And that's because different mutations in a gene effect the genes protein in different ways, right? So some mutations may be more detrimental than others. So that can increase the chance of the disease developing. So as we're chatting about these mutated genes that we're gonna get to that are relevant to Parkinson's Disease, we're just gonna say that they can cause the disease. But in the back of our minds we just have to remember that depending on which mutation in the gene is happening, because there can be quite a few different ones in one gene, and this is still being researched, right? The mutation can either 100% cause the disease or just increase the chances of developing a disease. Okay. So there are five main genes that we know about. So there are a few more but there's five main ones that when they're mutated in some way can cause Parkinson's Disease. So we won't go into all of these genes but let's go over a few of the genes that are a bit more commonly mutated. So let's head over here to our first chromosome. Chromosome #1. So here's our first chromosome so it's just-- it's just hanging out here. And right about here we have a gene called Park7, and Park7 it has instructions for making a protein called DJ-1. So here's DJ-1 here. And DJ-1 kinda makes me think of a mom, when I think about what DJ-1 does I think of-- I think of a mom. It does things like protecting and guiding. Right? Protecting and guiding our molecules around our body. You know, like how your mom protects and guides you, right? So, it helps protect our cells, it helps protect them during situations that stress our cells out. And it helps guide our proteins. So it helps guide them to do things like make sure they're folding in the correct three-dimensional shape. Because remember our proteins-- our proteins need to get into a certain shape in order to be able to function properly, right? And DJ-1 also helps to make sure that damaged proteins, proteins that we don't want anymore, are sent off to be broken down. Because otherwise they kinda pile up in our cells and they get in the way, right? Now, this last ones not very mom-like. I'm sure none of our moms would send us off to be degraded. But anyway... So those are some of the main tasks of DJ-1. So some mutations in the gene Park7 can cause Parkinson's Disease and Park7 is one of those genes where you need to get a mutated copy from both your mom and your dad in order to develop Parkinson's Disease. So this would be considered an Autosomal Recessive cause of Parkinson's Disease and it's actually responsible for early-onset Parkinson's Disease. So Parkinson's that's diagnosed before the age of 50 years old. So when Park7 is mutated, when the gene's DNA is changed in some way, that changes the instructions on how to make the DJ-1 protein, right? Because the gene carries a recipe for that protein. So when this is changed DJ-1 isn't made properly and therefore it can't function properly. It can't do all of these important mom-like tasks that we talked about. So that's Park7 and DJ-1. So, what's our next gene? Let's jump over here to Chromosome 6 and let's check out our next gene. So about here on Chromosome 6, about here, this is where our Park2 gene is. And for a mutation in this gene to cause Parkinson's Disease it would need to be inherited in an Autosomal Recessive way as well. A mutated copy from both your mom and your dad. Oh, and something that's really interesting is that the Park2 gene is one of the largest genes that we humans have in our whole body. So it's one of the biggest genes that we have. So Park2, it encodes for a protein called Parkin. So let's draw, let's draw a little Parkin protein here. And Parkin has this really, really important role. What it does is it tags other proteins that are damaged or that we have too many of, they're in excess. And it tags them with this molecule called Ubiquitin. So Ubiquitin is like a, it's like a little flag, it's a flag that alerts our cells to shuttle these proteins that we don't want-- that we don't want anymore. And it alerts them to shuttle them to these structures in our cells called Proteasomes. And this is where those proteins that we don't want get broken down and disposed of. So Proteasomes are kinda like the waste disposal facility in our cells. So Parkin is really, really important for making sure that we don't have all these excess or damaged proteins kinda piling up in our cells and getting in the way. So we actually know of a couple hundred different Park2 mutations that can cause Parkinson's Disease. So, some of the mutations are associated with the juvenile form of Parkinson's Disease which is essentially an extremely early-onset type of Parkinson's Disease relatively speaking to when it normally comes on. So, when people are diagnosed before the age of 20. And some other Park2 mutations, they're associaated with late-onset Parkinson's Disease, which is when people are diagnosed after the age of 50 years old. But in either case, whether it's early or late Parkinson's Disease, these mutations have changed the gene a bit, right? They've changed our instructions for making Parkin. And so we end up with a non-functional Parkin protein, a Parkin protein that just can't do what it needs to do. It can't function properly, it can't tag these damaged proteins so that we get rid of them. So our last gene that we're gonna look at is over here on Chromosome 12. So here's Chromosome 12 here, I'll just draw it out. And the gene that we're interested in is the LRRK2 gene. So I'm gonna call it Lark2, it's just a little easier to say. And it sits about here. So Lark2 gives us the recipe to make the protein Dardarin. And Dardain helps us do things like turn our cells on and off so that we can control their activity and send signals around the brain so that different cells can talk to each other. And what's really interesting is Lark2 mutations are actually the most common gene mutation that is associated with Parkinson's Disease. So this is the gene that we normally see issues with in people that have a genetic form of the disease. And with this particular gene people need to only get one mutated copy from either of their parents rather than both. So this an Autosomal Dominant genetic cause of Parkinson's Disease and just like before when our Lark2 gene gets mutated we end up with a malformed a damaged Dardarin protein being formed, right? So it's being produced by transcription and translation, but since we've damaged the Lark2 gene in some way the instructions are all wrong. So the protein ends up being formed a little differently so it can't function properly in order to carry out its really important roles. So we've gone through some of these gene mutations that can cause Parkinson's Disease but by now you must be wondering, "Yeah, I get that, I get that Park7 and Park2 and the Lark2 can get mutated and produce malformed proteins and then they can't do their jobs correctly, etcetera, etcetera, but what does that have to do with Parkinson's Disease? How does that cause Parkinson's Disease?" And that's an excellent question. And the answer as it stands right now is that we actually don't know. We don't know how these genes getting mutated and these proteins being malformed, we don't know how that actually leads to the disease. We just know that we consistently see Parkinson's Disease development in people with these gene mutations but we don't yet know, kinda step-by-step how people with these mutations actually develop Parkinson's Disease. So, for now, we'll just have to stay tuned into the ongoing research efforts to find out more about this one.