Ciliopathies and Retinal Degeneration

Part 1: Ciliopathies and Retinal Degeneration

00:00:07.12 Hello and welcome.
00:00:08.12 My name is Wallace Marshall from the Biochemistry Department at UCSF.
00:00:11.27 And today my colleague Jacque Duncan and I are going to be telling you about a
00:00:15.12 class of diseases of retinal degeneration, which are caused by defects in cilia,
00:00:20.06 a cellular component found in most cells of the body.
00:00:24.20 This image shows you a picture of a number of cells grown on a coverslip.
00:00:28.14 Each cell is outlined in red.
00:00:30.11 And then, within each cell, you can see these green objects.
00:00:32.20 These are the cilia.
00:00:33.20 These are hairlike projections from the cell.
00:00:35.15 And as you see, for these cells, every single cell has exactly one.
00:00:39.00 Now, these look very simple.
00:00:40.10 They look like small little hairs.
00:00:41.28 What we're going to try to tell you about today is that, in fact, these small, simple objects
00:00:46.04 are involved in an incredibly wide range of human diseases.
00:00:49.20 And in particular, we're going to focus on diseases that affect the retina.
00:00:53.00 So, here we have an image of cilia, shown in the collecting duct of the kidney.
00:00:57.23 And what you see is that they project into the lumen of the kidney, where the...
00:01:01.03 where the fluid would be flowing, the urine would be flowing.
00:01:04.06 And although these cilia look like very simple hairlike structures from the outside,
00:01:09.00 what we'll see is that when we look on the inside they're much more complicated.
00:01:13.10 So, this is a picture of the internal structure of a cilium.
00:01:16.20 As you can see, it looks very complex.
00:01:19.07 The cilium consists of an extension of the plasma membrane, the cell membrane,
00:01:24.09 shown here in yellow.
00:01:25.25 And this is a specialized membrane called the ciliary membrane that's full of sensory
00:01:29.28 receptors that can detect various chemicals in the media.
00:01:33.24 This membrane protrusion, as you see here, is pushed out from the cell surface by the
00:01:37.14 superstructure of proteins, as you see in the middle, here.
00:01:40.27 And there's a complex set of hundreds of proteins that form this complicated superstructure,
00:01:45.00 of which I've only diagrammed a few in this picture.
00:01:47.08 So, we see there are nine microtubule doublets, shown in blue, and these are the basic structural
00:01:51.27 components of the cilium.
00:01:54.00 These are connected together by various linkages.
00:01:55.28 In particular, they're connected by these dynein arms, the outer dynein arm and the
00:02:01.06 inner dynein arm, which provide the motile force for moving the cilium in cases
00:02:05.27 where the cilium has to move.
00:02:08.04 And there's a variety of other structures as well.
00:02:10.02 There are two other microtubules in the middle, called the central pair microtubules.
00:02:13.14 Those are found in some cilia but not others.
00:02:15.17 And various other structures.
00:02:16.26 It's highly complex, hundreds of proteins, and as far as we know there's probably a lot
00:02:22.04 of variation in which proteins are present in cilia of different cell types.
00:02:26.00 And the entire structure is built on a platform called the basal body, which is a highly modified
00:02:30.22 version of the centriole of the cell.
00:02:32.19 So, this structure is very complicated and that raises a couple of questions.
00:02:37.00 The... one question is, how does a cell build something that's this complicated?
00:02:40.16 You've got so many pieces.
00:02:41.16 How do you fit them all together in an orderly way?
00:02:44.09 The other question is, why do cilia have to be so complicated?
00:02:47.15 If all you're building is a simple hairlike structure, why do you need hundreds of proteins?
00:02:54.10 First we're going to address this first question of, how does a cell build this complicated structure?
00:02:59.05 And we now know that the building of a cilium involves a motile process called
00:03:02.11 intraflagellar transport, shown in this diagram.
00:03:05.08 Intraflagellar transport is an active motility operated by a kinesin-II motor proteins,
00:03:10.18 shown here in purple, which moves along these microtubules.
00:03:14.10 And it carries cargo out to the tip.
00:03:16.24 The way it carries the cargo is by interacting with a complex of 25 polypeptides called an
00:03:21.25 IFT particle, shown here by these yellow spheres.
00:03:25.01 The IFT particles themselves are not actually part of the cilium.
00:03:28.22 They're just like the bed of a truck that grabs cargo and carries it.
00:03:32.06 Then, these IFT particles aggregate into a long linear array known as an IFT train.
00:03:37.17 And then those IFT trains move all the way from the cell body out to the tip of the cilium,
00:03:41.11 drop off cargo like tubulin and other proteins,
00:03:44.16 where they can then assemble onto the growing structure.
00:03:47.04 And then the IFT trains come back to the cell body and get more cargo.
00:03:50.05 So, this process of intraflagellar transport is really the key machinery for building cilia.
00:03:54.24 So, at least part of the reason why the cell is able to make such a complicated structure
00:03:59.01 is this involvement of an active motility that can put... select the cargo that you want
00:04:02.19 and then put that cargo in the right place at the right time.
00:04:06.08 The second question is, why do cilia have to be so complicated?
00:04:10.22 One reason is because cilia have a lot of jobs to do.
00:04:13.19 Different cells have different cilia.
00:04:15.04 Almost every cell of the human body has cilia on it, but these cilia do different functions.
00:04:19.23 So, some cilia, as we show on top, are non-motile.
00:04:22.21 These cilia are probably playing sensory roles.
00:04:25.00 And there are non-motile cilia, for example, in the collecting duct of the kidney, in various
00:04:28.28 elements of the eye, and really many tissues in the body.
00:04:32.20 There are also cilia that are... that are motile.
00:04:34.25 So, examples are shown here.
00:04:36.20 The canonical example is motile cilia in the epithelium of your airway that are involved
00:04:41.04 in moving mucus.
00:04:42.21 But there's also cilia that are motile in the embryo and in the brain and other...
00:04:46.19 and oviduct and other places.
00:04:48.11 So, cilia have to do many different roles, sensory and motile, and probably that's
00:04:52.27 why they need to be such complicated structures.
00:04:57.12 So then, the question is, what does the function of cilia contribute to human physiology and health?
00:05:02.12 So, the... the first thing... really, evidence that cilia defects would cause disease came
00:05:07.12 from diseases in which motility of cilia was defective.
00:05:10.28 So, diseases in which cilia don't move properly.
00:05:14.06 And this is known as primary ciliary dyskinesia, or PCD.
00:05:18.11 And PCD has several different symptoms that patients can get.
00:05:22.25 One is bronchiectasis, shown on the left.
00:05:25.17 This is caused by a defect in clearing mucus out of the airway, so that the mucus starts
00:05:29.28 to pile up.
00:05:30.28 And this makes sense because you have cilia that are normally driving the flow of mucus.
00:05:34.20 If the cilia can't move properly, the mucus will simply accumulate.
00:05:38.15 And since one of the jobs of mucus is to get bacteria out of your lungs, if you can't clear
00:05:42.23 the mucus out, now the mucus sits around with bacteria in it, and you get inflammation
00:05:47.03 and infection, and it's quite debilitating.
00:05:48.17 There are also cilia moving mucus in your sinuses.
00:05:52.11 And so, similar to bronchiectasis, if you have ciliary motility defects, you typically
00:05:56.10 will suffer from chronic sinusitis.
00:05:59.16 In addition, about half the patients who have ciliary motility defects have what's known
00:06:04.05 as situs inversus, shown here.
00:06:05.28 Situs inversus means that all the organs inside your body are on the opposite side from where
00:06:09.28 they normally would be.
00:06:10.28 So, instead of your heart being on the left, now it's on the right, your spleen's on the
00:06:13.19 other side, and so on.
00:06:15.15 This actually is fine.
00:06:16.15 It doesn't make you sick.
00:06:17.15 You could have it right now and not know it.
00:06:19.15 But it's... it is a common feature in roughly half the patients with non-motile cilia,
00:06:23.25 and it's now known that this is because there are motile cilia in the embryo that
00:06:28.04 drive a flow of fluid, and the direction of that fluid flow determines which side of your body
00:06:32.17 is left and which side is right.
00:06:34.27 In addition, male patients are sterile because their sperm can't move, which it's...
00:06:39.09 kind of makes sense, because the flagella that drive your sperm motion are similar structures
00:06:43.08 to the cilia that drive flow of mucus.
00:06:46.16 So, there's class of diseases called primary ciliary dyskinesia.
00:06:51.02 And if the patients have situs inversus, this is known as Kartagener's syndrome.
00:06:55.05 This is important because it was the first recognized ciliopathy -- the first disease
00:06:58.17 caused by a defect in cilia.
00:07:02.22 This was discovered by Bjorn Afzelius, who studied Kartagener's patients and discovered
00:07:06.16 that they had defects in ciliary motility because the structure of the cilia was defective.
00:07:11.19 So, this is a cartoon showing a cross-section through the cilium.
00:07:14.24 And on top we see the complicated structures that are in there, including the dynein arms
00:07:18.27 that go from one doublet to the other.
00:07:21.02 And as the dynein arm walks along a doublet, it causes the entire cilium to bend, and that's
00:07:25.24 how mucus gets... gets then propelled.
00:07:27.01 On the bottom, we see on the left an electron micrograph of a similar cross-section through
00:07:32.20 a normal human patient.
00:07:34.18 And what you can see if you look carefully is that each outer doublet microtubule
00:07:38.03 has these two projecting hooks.
00:07:39.24 And those are the outer and the inner dynein arms that drive motility.
00:07:43.06 On the right, we see in a micrograph of a patient with PCD.
00:07:47.06 And you see the patient is missing a set of the dynein arms, and that's why the cilia
00:07:50.26 don't move.
00:07:51.26 So, when Afzelius discovered that Kartagener's syndrome was caused by defective ciliary structures
00:07:57.16 involved in motion, that was really the first clue that cilia could play an important role
00:08:01.17 in human disease.
00:08:05.20 Now, PCD and Kartagener's syndrome involved motile cilia.
00:08:10.03 These are typically found in large numbers on cells of the airway.
00:08:13.25 There was a whole other set of cilia, though, called primary cilia, which are found in almost
00:08:17.22 every other cell of the human body.
00:08:19.13 Typically, there's one primary cilium per cell.
00:08:22.14 They're not motile; they don't... they don't move.
00:08:25.03 They're now thought to be sensory structures and we know that they're jam-packed with receptors
00:08:29.12 and signaling molecules.
00:08:30.22 But, in the old days, no one knew what they did and there was the... the thought was out
00:08:34.23 there that they were just vestigial, irrelevant structures.
00:08:37.07 This was a quite widespread belief.
00:08:39.03 Now, you may ask yourself, how could anyone think that an organelle found in every cell
00:08:43.07 of the body is somehow vestigial and unimportant?
00:08:45.25 And that is quite a mystery, but that's what people generally tended to believe.
00:08:48.25 So, an interesting clue about cilia function came from a disease called polycystic kidney disease.
00:08:55.06 This is an incredibly common disease that affects 1 in 1000 people in the US.
00:08:58.19 And it's one of the leading causes of kidney failure.
00:09:02.04 Polycystic kidney disease is a disease in which the kidney becomes swollen with gigantic
00:09:06.00 fluid-filled cysts.
00:09:07.14 The kidney itself becomes extremely large, as shown here in the image.
00:09:10.20 And eventually it leads to kidney failure.
00:09:12.20 Before 1998, the cause of polycystic kidney disease was not known.
00:09:17.16 However, there was a mouse mutant that was called Tg737.
00:09:21.11 This was a random mutation of a particular gene called transgene 737.
00:09:26.07 Nobody knew what the gene did.
00:09:27.26 They could show, however, that mutations in this gene caused the kidney to be filled with
00:09:32.03 gigantic fluid-filled cysts.
00:09:34.04 And therefore it became a model for polycystic kidney disease.
00:09:37.12 But at the time it was found, and for many years afterwards, nobody knew why this mutation
00:09:41.17 caused the formation of cysts in the kidney.
00:09:44.20 The clue came from an even more unlikely, potentially, source, which is green algae.
00:09:48.10 So, it turns out a green alga called Chlamydomonas reinhardtii, shown here, has really been critical
00:09:53.26 for learning a lot of what we know about cilia.
00:09:57.20 The reasons are twofold.
00:09:58.23 One, Chlamydomonas has very easy genetics, so if you want to do genetic studies you can
00:10:03.17 do thousands of more studies in a given amount of time in Chlamydomonas than you could with
00:10:07.26 a mouse, which is very slow and difficult to work with.
00:10:10.19 Also, biochemistry is very good, so you can isolate the cilia from this organism
00:10:14.17 very cleanly and easily.
00:10:16.09 One point of terminology in Chlamydomonas, these cilia are referred to as flagella.
00:10:21.06 And what you'll see if you study this field is that different organisms and different
00:10:24.09 cell types make call the structure of cilia or they may call it flagella.
00:10:28.04 The two terms mean exactly the same thing.
00:10:30.10 They're just two different words for the same structure, just like morning star and evening star.
00:10:34.13 So, workers studying the flagella of Chlamydomonas, which is the cilium of this green alga,
00:10:39.21 made a really key discovery, which is the discovery of this intraflagellar transport process that
00:10:43.24 I told you about.
00:10:45.21 This was discovered in Joel Rosenbaum's lab by Keith Kozminski.
00:10:49.03 And they were looking at motility within this flagellum using video microscopy.
00:10:54.02 And what they could see, when they looked at images like the one on the left at
00:10:57.02 very high resolution, is they could see particles moving back and forth.
00:11:01.02 Then, harnessing the genetics of this organism, they were able to find a mutation, a mutation
00:11:05.00 in the kinesin which was previously known, but that... then, they learned that this mutation
00:11:09.27 caused IFT motility to stop.
00:11:12.06 And the particles to apparently not be in the flagellum anymore.
00:11:15.21 That was then the key tool that Douglas Cole in the Rosenbaum lab used to try to purify
00:11:20.07 these IFT particle proteins.
00:11:22.13 What he did was to isolate the cilia from the cells biochemically, which is very easy
00:11:26.04 to do in this organism, unlike mammalian cells where I can attest it's very difficult.
00:11:30.22 And then compared what proteins he saw in the cilia from mutants that had...
00:11:35.14 that lacked IFT to normal cells that had IFT.
00:11:38.18 And he found a set of proteins that were missing in the mutant that didn't have IFT, and so
00:11:42.04 he called those the IFT proteins.
00:11:44.19 And so when I showed you images like this one before, I told you there's a complex of
00:11:48.10 25 or so polypeptides that make up this IFT particle.
00:11:51.27 Those are the IFT proteins that Doug Cole first started discovering.
00:11:55.04 And it was this discovery that really launched the modern field of ciliopathy.
00:12:00.09 Because, when they started sequencing the different proteins and determining their identity,
00:12:04.28 they discovered that one of these proteins, IFT88, was in fact Tg737, the gene which when
00:12:11.02 mutated caused polycystic kidney disease in this well-known mouse model.
00:12:15.17 Somehow, when this... when the IFT is missing, the cell can no longer build cilia.
00:12:20.22 So, the cells lose cilia.
00:12:22.11 And then, somehow, that leads to polycystic kidney disease.
00:12:25.15 The big question is, why does the cell... why does the kidney care whether the cells
00:12:29.04 have cilia or not?
00:12:30.04 What do cilia have to do with the kidney?
00:12:32.21 It turns out that the reason why the kidney cares about cilia is because cilia act as
00:12:37.16 sensors of urine flow.
00:12:39.07 So, the cilia project into the collecting tubules of the kidney and as the fluid
00:12:43.22 flows by it bends the cilia.
00:12:46.09 And as shown in this diagram, the cilia contain channels that open in response to this flow
00:12:50.15 and lead to a calcium transient inside the cell.
00:12:53.23 The cells then interpret this calcium level and adjust their own behavior.
00:12:57.12 Now, we know that if cells don't have the cilia, they can't respond to the flow and
00:13:01.23 generate these calcium signals.
00:13:03.14 So, how does that lead to cysts?
00:13:05.10 Well, the current idea is that if cells don't have the flow they try to obtain the flow
00:13:12.01 by proliferating.
00:13:13.17 And when the cells proliferate, they're trying to basically grow a new tube to try to
00:13:17.10 get out to where the rest of the flow is.
00:13:19.20 And this attempt to make a tube when they aren't supposed to be doing that leads to
00:13:22.24 the formation of cysts.
00:13:24.02 So, the basic idea is that, when you have a defect in cilia, either the cilia are missing
00:13:29.03 or because the cilia don't contain some of these receptor channels for flow,
00:13:33.21 then the cells think they need to keep proliferating, and so they overproliferate and that
00:13:37.19 makes these gigantic cysts that cause polycystic kidney disease.
00:13:42.26 But it turns out cystic kidneys are not the only defect we see in mutations that affect
00:13:47.00 primary cilia.
00:13:48.26 Another example is the IFT80 protein, another one of these IFT proteins.
00:13:53.06 Mutations in IFT80 cause cystic kidneys but also other defects.
00:13:58.18 And collectively this disease is called short-rib polydactyly.
00:14:02.08 So, this is a syndrome that's characterized by not only kidney cysts, but also extra fingers
00:14:07.15 and toes, shown here in this picture.
00:14:09.17 So, we already understand why an IFT defect could give rise to kidney disease, because
00:14:15.00 you're losing this ability of this... losing these flow sensors, the cilia in the kidney.
00:14:19.02 But what do cilia have to do with extra fingers and toes?
00:14:22.15 Well, it turns out that cilia not only are sensing mechanical stimuli like fluid flow,
00:14:29.17 they're also involved in sensing and transducing chemical signals.
00:14:33.01 In this case, there's a chemical ligand called hedgehog, which signals position along the
00:14:37.17 vertebrate limb.
00:14:38.17 So, it's a tem... it helps cells know whether they should make a certain kind of finger
00:14:41.15 or a certain kind of toe where they are in the growing limb bud.
00:14:45.16 The hedgehog protein itself binds to a receptor on the cell surface, which then triggers biochemical
00:14:50.25 events inside the cilium, which lead to changes in processing of transcriptional regulators,
00:14:55.21 which, as shown in this diagram, ultimately affect transcription of genes inside the cell,
00:15:00.11 which help determine cell fate.
00:15:02.16 And a number of studies shown here have found that various components of this hedgehog signaling pathway
00:15:08.06 are either localized within the cilium or are influenced by events that occur within
00:15:12.13 the cilium.
00:15:13.13 So, the idea is that, when you have ciliary defects, for example, in IFT mutants,
00:15:17.21 not only will you have kidney problems, you'll also have problems developing tissues that
00:15:21.17 require hedgehog signaling, such as limb buds, and that's how you get polydactyly.
00:15:28.16 So, what you can see is that cilia cause a wide range of symptoms.
00:15:32.19 And there's many more symptoms than what I've told you about so far.
00:15:35.22 And we think that these various symptoms have to do with differences in the composition
00:15:39.17 of the cilia in different cell types.
00:15:41.11 And so many of us are interested in learning more about the complexity of cilia.
00:15:45.15 What are all the proteins that are in there?
00:15:47.12 What are all the genes that encode these proteins and what do they do and how they relate to
00:15:50.14 human disease?
00:15:52.13 There been many efforts to look at the proteome, that is, the full protein composition of the
00:15:56.06 cilia themselves.
00:15:57.17 We ourselves have been looking at one particular part of the cilium, which is the basal body
00:16:00.22 I told you about, the platform on which you build the cilium.
00:16:04.03 Now, within a cell, there's a structure called the centriole, which is shown here on the left.
00:16:09.06 The centriole is a barrel of nine microtubule triplets, which in interphase is involved
00:16:14.01 in building the centrosome, so, the structure that's going to nucleate the skeleton of the cell
00:16:18.15 and also is involved in cell division.
00:16:20.26 But in addition to its role in forming the centrosome, the centriole can also move to
00:16:25.04 the surface of a cell, as shown here, and in this case it docks on the surface of the cell
00:16:29.15 and then nucleates the formation of a cilium.
00:16:31.27 And at that point, it's called a basal body.
00:16:33.21 And you can see in this electron micrograph there's a basal body here at the base,
00:16:37.24 and then the cilium grows out from that.
00:16:40.00 So, our thinking is that, if one of the roles of the basal body is to build a cilium,
00:16:45.17 maybe there will be interesting proteins in the basal body, not in the rest of the cilium,
00:16:49.22 that play some role in the complex functions of the cilium.
00:16:53.10 So, we wanted to know, what is the protein composition of the basal body?
00:16:58.08 Several labs had looked at the protein composition of isolated cilia and found a number of interesting
00:17:02.08 ciliary disease gene encoded proteins.
00:17:05.14 Proteins involved in polycystic kidney disease.
00:17:08.03 Proteins involved in Kartagener's, hydrocephalus, and many other interesting cilia-related diseases.
00:17:13.08 Interesting and debilitating for those who have them.
00:17:16.00 What about the basal body?
00:17:17.13 It's needed to make cilia.
00:17:18.28 It's at least as complicated in its structure as the cilia themselves.
00:17:22.23 Will it have a different set of proteins?
00:17:24.08 So, to answer this question, we went back to Chlamydomonas reinhardtii, this green alga
00:17:28.11 that was used to discover IFT.
00:17:30.22 We can grow it in huge quantities.
00:17:32.13 So... so, as shown here, we grow in typically in eight liter jugs under a fluorescent light.
00:17:38.11 And then we were able to isolate the basal bodies from these cells, as shown here
00:17:42.09 in the right panel.
00:17:43.26 Once we had the basal bodies isolated, our friend John Yates did the proteomic analysis
00:17:47.20 for us on this sample.
00:17:50.03 When we looked at the proteins that made up the basal body, we got an interesting result.
00:17:55.24 It turns out that a substantial number of the proteins we found in the basal body corresponded
00:18:01.07 to genes that were already known to cause cilia-related defects, or the defects that
00:18:06.13 you could in principle relate to cilia.
00:18:09.00 And here I'm just showing an example of some of them.
00:18:11.11 So, for example, Cep290 causes a kidney disease called nephronophthisis
00:18:15.28 and also retinal degeneration.
00:18:17.15 NPHP4 gives you... if you have mutations in that,
00:18:20.27 you have nephronophthisis and retinal degeneration.
00:18:24.06 And what we see is that a number of these diseases involving basal body proteins seem
00:18:28.17 to have a syndrome called retinal-renal ciliopathy.
00:18:31.27 That is, you see this combination of defects in cilia and in the retina.
00:18:35.08 And it raises the question, how does this one set of proteins found on the basal body
00:18:39.24 cause these two kinds of symptoms again and again?
00:18:46.13 It turns out, if you look at where the proteins that cause retinal-renal ciliopathy localize,
00:18:52.11 they localize to the very end of the basal body,
00:18:54.27 a region that we call the transition zone,
00:18:56.24 which is the junction between where the basal body is and where it forms the cilia.
00:19:01.27 And if you look in cross-section, there's these very interesting star-shaped structures
00:19:05.00 that form in this transition zone.
00:19:06.09 And I think it's fair to say we still don't know all the proteins that are in this region.
00:19:10.15 So, it is proteins that localized to this transition zone that appear to cause these
00:19:16.05 problems both in the kidney and in the retina.
00:19:18.07 And the question is, why?
00:19:19.07 Why... why do you have so many defects?
00:19:22.01 Part of the reason could be because basal bodies actually do at least two things.
00:19:26.25 One is that the basal bodies move to the cell surface and dock onto the cell surface.
00:19:31.21 And that's where they form the cilium.
00:19:33.03 So, they're forming a mechanical anchor.
00:19:34.27 So, you can imagine that defects in that mechanical anchoring could have various umm... could
00:19:39.17 have various phenotypic consequences and cause, potentially, disease symptoms.
00:19:44.11 In addition, this transition zone is apparently acting as a barrier just to keep just random
00:19:49.24 proteins from the cell getting into the cilium.
00:19:52.01 So, if this... if this zone is acting as some kind of selectivity filter, then you could
00:19:56.20 imagine that defects in proteins of the transition zone would cause defects in which proteins
00:20:01.23 get into the cilium and which ones don't.
00:20:07.13 In thinking about some of these functions, it's very important also to distinguish between
00:20:11.08 nephronophthisis, which is what's caused by mutations in these transition zone proteins,
00:20:16.02 from normal polycystic kidney disease, which is what we previously talked about with the
00:20:21.07 Tg737 mutant.
00:20:22.28 So, polycystic kidney disease, shown on the left, is an adult-onset disease in which kidneys
00:20:27.25 become extremely large and the cysts that you... that form are round or spherical.
00:20:33.08 Nephronophthisis, although it affects kidneys, is really quite different.
00:20:36.25 It's very early onset.
00:20:38.10 It's juvenile onset in children.
00:20:40.09 The cysts are not round.
00:20:41.14 They're tubular.
00:20:42.15 And the overall size of the kidney is not any different.
00:20:44.20 The kidney is still normal-sized.
00:20:45.22 So, although both of these are cystic kidney syndromes, they really are quite different
00:20:50.16 in their phenotype.
00:20:52.05 And I think it's fair to say that we still don't really understand exactly how
00:20:56.02 these two different kinds of symptoms arise.
00:20:58.27 There's a hypothesis... there's a hypothesis currently being discussed about where nephronophthisis
00:21:04.01 comes from that's quite different from what I previously told you about for
00:21:07.13 polycystic kidney disease.
00:21:09.06 And the idea here is that, normally, as shown on the left, when a kidney is developing,
00:21:14.27 cells will orient their divisions to make a tube of the correct length and diameter,
00:21:18.10 and this becomes the collecting ducts of the kidney.
00:21:21.17 If you had randomization of the spindle orientation, so if the cells were dividing in random directions
00:21:26.03 instead of along the length of the tube, then what would happen is you would get these
00:21:30.03 very wide tubes, similar to what you see in nephronophthisis.
00:21:32.24 And, in fact, in various animal models of this disease, when researchers have gone and
00:21:38.25 looked at spindle angles, they can find that in fact there is a randomization of
00:21:43.00 spindle angles in these nephronophthisis animal models.
00:21:47.04 This would fit with the idea that maybe it's the anchoring function of the basal body
00:21:51.09 that's involved in anchoring the structure to the surface of the cell.
00:21:54.20 And therefore helping the spindles orient in the correct direction.
00:21:58.00 And when you have this defective anchoring and orientation, you would then have randomization
00:22:01.25 of which way the cells were dividing, and that will give you nephronophthisis.
00:22:05.24 This is still a controversial hypothesis.
00:22:08.01 Not everyone agrees with this and it may be wrong.
00:22:10.06 But it's interesting to think about... there could be functions of the basal body that
00:22:14.12 really aren't related to ciliogenesis per se.
00:22:17.08 And it's important to always bear that in mind.
00:22:21.13 But none of this answers the question of, why are there also retinal symptoms?
00:22:25.26 And to answer that question I will now yield the floor to my esteemed colleague from the
00:22:29.01 Ophthalmology Department, Dr. Jacque Duncan.
00:22:31.03 Thank you very much for your attention.

Part 2: Ciliopathies and Retinal Degeneration

00:00:07.03 Hello, my name is Jacque Duncan, and I am going to pick up where my esteemed colleague
00:00:12.12 Wallace Marshall left off.
00:00:14.24 And explain to you today some of the consequences of ciliopathies that affect retinal structures
00:00:21.13 when transport can't keep up with turnover.
00:00:24.24 As Wallace was mentioning earlier, cilia represent important structures in many cells in the body.
00:00:32.04 And, in fact, the retinal... umm... the retinal photoreceptors, or vision cells, contain an
00:00:38.02 important ciliar structure called the connecting cilium.
00:00:41.12 Many genes that cause the photoreceptors to gene... to degenerate and die encode proteins
00:00:46.24 that localize to that connecting cilium.
00:00:49.21 And some of those proteins are also expressed in cilia in other parts of the body,
00:00:54.06 such as the kidneys and the cerebellum.
00:00:58.05 When these mutations affect photoreceptor cells, many different types of mutations that
00:01:03.24 localize to the cilia can cause the photoreceptor cells to die.
00:01:08.15 Oftentimes, the rods are affected first, in which case a disease is called retinitis pigmentosa,
00:01:15.09 or rod cone degeneration.
00:01:17.17 Other times, the cone photoreceptors, which help us see colors and fine details, are affected
00:01:23.02 earlier.
00:01:24.02 In those cases, it would be considered a cone rod dystrophy.
00:01:28.24 Additional very severe forms of retinal degeneration affect children in infancy and cause
00:01:34.20 very severe vision loss very early in life.
00:01:37.09 And that condition is known as Leber congenital amaurosis.
00:01:41.17 All three of these types of diseases can be caused by mutations that affect cilial proteins.
00:01:47.15 Sometimes, as is not perhaps surprising based on the talk earlier this morning,
00:01:53.18 patients can have not only problems with their retina but also problems elsewhere in the body.
00:01:58.25 Some patients have retinal degeneration in association with hearing loss.
00:02:03.09 That constellation of findings is known as Usher syndrome.
00:02:07.19 Other findings can include situs inversus, disorders of limb and digit development, obesity,
00:02:14.14 learning difficulties, or developmental delay, problems with the liver or kidneys,
00:02:19.16 and reduced sperm motility or abnormal sperm structure with reduced fertility.
00:02:26.17 This slide shows a histological section of the retina, which demonstrates the well-organized
00:02:31.17 layers that include different cells of the retina.
00:02:35.07 The vision cells are located adjacent to the eye wall.
00:02:39.17 And their cell bodies are located next to their inner segments and outer segments.
00:02:44.11 The outer segments are the parts of the retina, photoreceptors, that turn light into a message
00:02:49.08 that the brain can understand.
00:02:51.27 This slide shows an optical coherence tomography scan, OCT scan.
00:02:56.21 This is a type of picture we can obtain in the retina clinic of the layers of the retina
00:03:01.27 in cross-section, from living eyes, non-invasively.
00:03:05.09 The technology uses near-infrared light, which is reflected differently by the different
00:03:11.00 layers of the retina.
00:03:12.20 The layers of the retina that contains cell bodies, or the nuclear layers, tend not to
00:03:17.11 reflect light as much as the plexiform layers, were the axons and synapses of the retina reside.
00:03:25.15 Because the cell body layers are interspersed with the synaptic layers, we can obtain a
00:03:31.14 very nice layered structure of the... image of the retinal structure non-invasively from
00:03:36.18 patients using this technique in the clinic.
00:03:38.24 I'd like to call to your attention some of the layers in this OCT scan that represent
00:03:44.27 the locations of the photoreceptors.
00:03:47.26 The dark layer I'm showing you now is the location of the photoreceptor cell bodies,
00:03:52.25 where the rod and cone nuclei reside.
00:03:55.14 Then, there's a bright line separating the nuclear layers from the inner segments of
00:04:02.14 the photoreceptors, where all the mechanics and machinery necessary to generate proteins resides.
00:04:09.14 There's a bright band called the connecting cilia band, which connects the inner segment
00:04:15.22 to the outer segment of the photoreceptor.
00:04:17.22 And at this location, the photoreceptor connecting cilia reside.
00:04:20.28 They play an important and critical rule in trafficking proteins from the inner segments,
00:04:25.26 where the proteins are synthesized, to the outer segments located in this somewhat dark band,
00:04:30.14 where they are necessary to turn light into a message that the brain can understand
00:04:36.00 through a process known as phototransduction.
00:04:39.11 And, in patients with retinal degeneration, we can monitor the presence and integrity
00:04:45.10 of this bright connecting cilium band to determine the extent to which photoreceptors have degenerated
00:04:51.18 and died.
00:04:52.18 Again, showing this histological section of the retina, if we focus our attention on the
00:04:58.11 parts of the retina that actually do the work of turning light into a message the brain
00:05:02.19 can understand, the inner and outer segments, shown here, and magnify this, studying it
00:05:08.17 with an electron microscope rather than a light microscope,
00:05:11.24 you can see that the inner segment machinery of the cell is connected to the outer segment discs,
00:05:19.00 which phototransduce light into a chemical message that the brain can understand by the connecting cilium,
00:05:25.08 shown here.
00:05:27.12 This is the cilial structure that characterizes all photoreceptor cells.
00:05:31.17 It is important not only for photoreceptor structure but also for photoreceptor trafficking
00:05:38.08 of proteins that are synthesized in the inner segment
00:05:41.18 and then transferred down to the outer segment,
00:05:44.05 where they are necessary to allow the light to be turned into a message the
00:05:47.19 brain can understand.
00:05:48.19 So, you can understand that proteins that localize to the important connecting cilium
00:05:53.22 can cause problems with the photoreceptors, and can even cause them to die.
00:06:00.15 Photoreceptor cilia are somewhat similar to the cilia you heard about earlier in this talk.
00:06:05.19 They are primary cilia, non-motile cilia, and they have a 9+0 structure.
00:06:10.06 They connect the inner segments of the photoreceptors to the outer segments.
00:06:14.16 And every protein that the vision cell needs, photoreceptor needs, to turn light into
00:06:20.06 a message the brain can understand through a process known as phototransduction,
00:06:25.05 as well as proteins necessary to keep the outer segments alive and working,
00:06:30.02 must be made in that inner segment part of the cell
00:06:33.26 and transported to the outer segment by that essential connecting cilium structure.
00:06:40.19 When cilia proteins are mutated or abnormal, retinal degeneration can occur.
00:06:46.16 Because normal cilia are required for normal function, not only of the retina but also
00:06:50.22 of the inner ear, the brain, and the kidneys.
00:06:52.26 So, it's sometimes causing syndromic forms of retinal degeneration.
00:06:56.08 And again, photorecp... retinal degenerations
00:06:59.20 can sometimes affect that specialized photoreceptor cilium,
00:07:02.06 with or without effects on other types of cilia in the body.
00:07:07.15 The first example I'll tell you about today is caused by a cilia protein known as RPGR,
00:07:14.13 which stands for retinitis pigmentosa GTPase regulator.
00:07:19.15 This gene is mutated about 70% of the time in patients who have inherited retinitis pigmentosa
00:07:25.20 in an X-linked fashion.
00:07:27.05 It's a gene encoded on the X chromosome.
00:07:30.16 It's also mutated or changed in about 25% of male patients with retinitis pigmentosa
00:07:37.17 with no clear history of X-linked inheritance.
00:07:41.03 And it's an abnormal gene change in about 11% of retinitis pigmentosa overall,
00:07:46.15 making it an important cause of retinal degeneration.
00:07:49.20 It plays an important role in formation of the photoreceptor outer segment discs by
00:07:55.15 interacting with a protein called RPGR-interacting protein, or RPGRIP.
00:08:01.08 And also plays an important role in trafficking of a protein called opsin, that is necessary
00:08:06.14 for normal phototransduction and photoreceptor cell survival.
00:08:11.08 This is a fundus photograph, or a picture of the back of the eye, from a patient with
00:08:16.18 X-linked retinitis pigmentosa.
00:08:18.13 This 19-year-old patient had a mutation in the RPGR gene that resulted in a frameshift
00:08:26.05 encoding that protein, and causing it to be truncated early
00:08:30.12 and perhaps not functioning normally.
00:08:33.02 This 19-year-old patient presented with difficulty with night vision and difficulty with side vision.
00:08:39.02 He retained good central vision, however, until his... the age of the examination,
00:08:44.24 which in this case was 19.
00:08:46.13 You can see in this fundus photograph that, compared to a normal 19-year-old,
00:08:51.09 in this patient the optic nerve is somewhat pale, the vessels are somewhat narrow,
00:08:56.20 and, if we look further out at the edges of the eye,
00:09:00.08 you can see this black pigment change, which
00:09:03.02 is a cur... is known as bone spicule pigmentary change.
00:09:06.26 And that occurs in areas where the photoreceptors have gone away and died.
00:09:11.05 However, right in the center of his retina, which is the area responsible for
00:09:15.24 central visual acuity, the retina is more normal.
00:09:19.11 And his vision in... at this time was approximately 20/30.
00:09:24.14 The reason it was 20/30 can be seen in this optical coherence tomography scan.
00:09:29.21 Unlike the normal scan I showed you earlier in this talk, you can see that at the very
00:09:33.19 center of the retina we see dark spaces.
00:09:37.13 These dark spaces are cysts, which represent fluid accumulating in the very center of the retina.
00:09:44.20 Another abnormality that we can see on this OCT scan, which is a little more subtle but
00:09:49.21 I'll demonstrate to you with a higher magnified scan,
00:09:53.17 is that that important inner segment-outer segment junction band,
00:09:57.19 shown here in white,
00:09:59.22 is only present right in the center,
00:10:02.05 where the patient's visual acuity is good.
00:10:04.08 You'll notice that at the edges of this scan that band is absent.
00:10:07.27 And that indicates that the photoreceptors beyond the very center of the retina
00:10:12.19 have degenerated and died, even at the age of 19 in this patient.
00:10:17.07 So, an even more severe form of retinal degeneration is known as Leber congenital amaurosis,
00:10:24.01 or LCA.
00:10:25.01 This presents with very severe vision loss in infancy or early childhood.
00:10:30.00 And the vision loss in this case is due to death of the photoreceptors at very early ages.
00:10:36.05 Children with LCA present with abnormal eye movements called nystagmus.
00:10:40.15 They're often farsighted or hyperopic.
00:10:43.10 And many of them rub on their eyes in what is believed to be an attempt to stimulate
00:10:47.20 some perception at the visual cortex due to mechanical stimulation, given that the photoreceptors
00:10:53.12 are not responding to light.
00:10:55.24 Children with LCA sometimes have an abnormal pupil response to light, where, when you shine
00:11:00.28 a light in the pupil, rather than constricting as it normally should, the pupils dilate.
00:11:07.05 LCA has been associated with at least 14 and perhaps even 17 different genetic mutations.
00:11:13.25 At least 2 to 3 of these are associated with mutations in proteins that localize to the cilia.
00:11:20.13 And 2 of these are RPGRIP1 and, as Wallace mentioned earlier, CEP290, or NPHP5.
00:11:29.08 RPGRIP1 causes a very rare form of Leber congenital amaurosis, affecting only about 6% of children
00:11:36.24 with this disease.
00:11:37.24 However, it is an important protein that forms an axoneme component of the connecting cilium
00:11:43.13 of photoreceptors.
00:11:44.13 It is an important protein to anchor the ret... retinitis pigmentosa GTPase regulator, or
00:11:50.27 RPGR protein, that I mentioned in the patient with X-linked retinitis pigmentosa that caused
00:11:56.19 vision loss later in life.
00:11:59.02 This protein regulates the actin cytoskeleton reorganization as new discs are being formed
00:12:06.02 on a daily basis.
00:12:08.04 When it is absent, proteins do not traffic normally from the inner segments to the
00:12:13.05 outer segments, resulting in disorganized outer segments.
00:12:16.10 And the protein opsin, which is necessary for normal phototransduction, becomes mislocalized
00:12:22.01 to the cell nucleus.
00:12:23.16 If it's not able to get into the outer segments, phototransduction cannot occur and children
00:12:28.11 cannot see.
00:12:29.20 This is a fundus photograph of a child with Leber congenital amaurosis, also showing
00:12:34.26 pallor of the optic nerve, attenuation of the vessels, and pigmentary changes.
00:12:40.06 Unlike the patient I showed you a few minutes ago, this picture was taken from an infant
00:12:43.23 under anesthesia, demonstrating that this is a very early onset form of retinal degeneration.
00:12:49.25 We can measure how well the vision cells are responding to light, objectively, in children
00:12:55.06 that are very young, and in older people as well,
00:12:58.19 using a contact lens with a wire in it on the eye.
00:13:02.25 This is analogous to an electrocardiogram, where electrodes are used to measure electrical responses
00:13:09.00 that the heart makes whenever it beats.
00:13:11.06 This test is known as an electroretinogram, which measures electrical responses that the
00:13:17.17 retina creates whenever it responds to light.
00:13:20.26 This child with Leber congenital amaurosis has an electroretinogram which is shown at
00:13:25.16 the bottom of this slide.
00:13:27.04 And in response to dim lights that should only stimulate the nighttime vision cells,
00:13:31.09 or rods, as well as bright lights that should only dem... stimulate the daytime vision cells,
00:13:36.24 or cones, the patient's electroretinogram is essentially unmeasurable,
00:13:41.07 suggesting that both the photoreceptor types,
00:13:44.06 the rods and the cones, are severely dysfunctional and
00:13:47.17 their responses are nearly absent in this young child with Leber congenital amaurosis.
00:13:52.15 As I mentioned before, ciliopathies can affect not only the retina but also other cell types
00:14:00.04 in the body.
00:14:01.11 As Wallace had mentioned, often times cilia mutations will cause not only retinal degeneration
00:14:07.02 but problems with the kidneys, known as nephronophthisis,
00:14:10.19 which is for... causes progressive death of the renal cells and tubules.
00:14:14.19 A condition known as Senior-Loken syndrome is characterized by retinitis pigmentosa plus
00:14:21.08 nephronophthisis.
00:14:22.08 And this occurs in about 10% of patients who
00:14:25.09 have mutations in genes called NPHP1 through NPHP4.
00:14:31.25 There's a gene known as NPHP5, which caused Senior-Loken syndrome associated with
00:14:36.26 cystic kidney disease
00:14:39.10 and early onset retinal degeneration, which rarely can also cause
00:14:42.24 Leber congenital amaurosis in the absence of any kidney disease.
00:14:47.00 And this occurs... accounts for only about 3% of patients with LCA.
00:14:53.27 Another syndromic form of Leber congenital amaurosis associated with mutations that affect
00:14:58.06 the cilia is caused by a gene called NPHP6 or CEP290, and Wallace mentioned this gene
00:15:06.21 in his part of the talk.
00:15:08.08 It causes... it's a very common cause of Leber congenital amaurosis, responsible for about
00:15:13.16 20% of these cases.
00:15:16.11 This gene localizes to the centrosome and connecting cilia of the photoreceptors,
00:15:22.09 and associates with the two proteins I mentioned earlier in this talk, RPGR and RPGRIP1.
00:15:29.28 It also sometimes causes a disease called Joubert syndrome.
00:15:33.18 Joubert syndrome is characterized by dysfunction of the kidneys, the retina, and the cerebellum.
00:15:40.19 The cerebellar disease causes a very interesting and somewhat unique finding that is visible
00:15:46.02 on histological sections and also MRI scans of the brain, in which the cerebellar vermis
00:15:52.07 tissues are hypoplastic or dysplastic.
00:15:55.09 Their fibers do not cross the central midline or decussate, resulting in a feature on MRI scan
00:16:02.08 that can help with... assist with the diagnosis of this disease,
00:16:05.23 known as the molar tooth sign.
00:16:08.08 And I'll show you that picture... a picture of that molar tooth condition in the next slide.
00:16:14.11 Patients with this disease also have thick, elongated cerebellar peduncles, which contribute
00:16:18.21 to the molar tooth finding, and a deep posterior interpeduncular fossa.
00:16:24.10 This is felt to be a consequence of defective axon guidance in the absence of normally functioning
00:16:30.06 cilia.
00:16:31.09 There's no crossing of the superior cerebellar peduncle structures.
00:16:35.10 Interestingly, a mouse with mutation in a gene called Rd16
00:16:40.27 also has early onset retinal degeneration.
00:16:44.18 And this is the mouse equivalent of the CEP290 gene.
00:16:48.06 This MRI scan pan... slide shows a patient with Joubert syndrome at the top, and a
00:16:55.00 normal subject at the bottom.
00:16:56.13 And you can see the cerebellum is shown in the middle of this slide.
00:17:00.11 And, unlike the normal cere... cerebellum shown at the bottom of this slide, which looks
00:17:04.26 a little bit like a butterfly, the patient with Joubert syndrome has an appearance of
00:17:09.28 almost a... a molar tooth, with very elongated cerebellar peduncles.
00:17:16.05 This is also seen in another section, shown here, where, again, the cerebellar vermis
00:17:20.15 is hypoplastic or dysplastic.
00:17:22.17 And there's a big space between the two sections because the axons are not crossing normally,
00:17:28.25 as they should, in the absence of the function of this normal ciliary protein.
00:17:34.01 So, interestingly, CEP290 and RPGRIP1 both cause Leber congenital amaurosis.
00:17:42.19 Both of these are photoreceptor ciliary proteins.
00:17:45.23 Both of them cause early onset and very severe degeneration of the rod cells, subsequently
00:17:51.11 followed by a generation of the cone cells.
00:17:54.26 But, importantly, the central cones in both of these diseases tend to be spared until
00:17:59.17 later in life, resulting in some residual central vision for patients with these mutations.
00:18:06.08 Retinal degenerations can also be associated with other proteins
00:18:09.17 that localize to the connecting cilium or other ciliopathies.
00:18:12.28 A large and somewhat uncommon but important class of retinal degenerations is known as
00:18:18.22 Bardet-Biedl syndrome.
00:18:20.21 This disease... class of diseases causes retinal degeneration, again, because mutations that
00:18:26.27 affect the connecting cilium in the outer retina result in photoreceptor dysfunction
00:18:31.12 and death.
00:18:32.12 We can monitor that connecting cilium band, carefully, in the clinic, non-invasively,
00:18:37.27 using a spectral domain optical coherence tomography scan, which I showed you earlier
00:18:42.10 during this talk.
00:18:44.04 In addition to retinal degeneration, Bardet-Biedl syndrome includes systemic findings, including
00:18:49.25 obesity, extra fingers and toes -- known as polydactyly --
00:18:55.09 general abnormalities such as hypogonadism,
00:18:59.22 about half of patients have difficulty smelling,
00:19:02.08 and many patients have hearing loss,
00:19:05.13 again, manifestations of mutations in proteins that affect the critical ciliar
00:19:11.05 structures of a number of different tissues in the body.
00:19:14.27 This slide shows a picture of polydactyly of the feet, showing an extra toe.
00:19:21.05 And a patient who had had polydactyly of the fingers, where... who was 56 years old and
00:19:27.10 the polydactyly, or the extra fingers, had been removed early in life.
00:19:30.17 So, sometimes the only clue that a patient had polydactyly will be surgical scars on
00:19:35.22 the fingers of older or adult patients.
00:19:38.07 This patient had a mutation in a gene known as BBS10.
00:19:42.14 And you can see that patients with Bardet-Biedl syndrome have retinal degeneration that sometimes
00:19:48.24 affects even the central retina, or the macula, resulting in central... severe central vision loss.
00:19:55.06 In this patient with advanced retinal degeneration, due to a mutation in BBS10, the... you can
00:20:01.20 see widespread loss of the photoreceptors, as manifested by pigmentary changes, really,
00:20:07.00 throughout the fundus.
00:20:08.09 In addition, the optic nerves are very pale and the retinal vasculature is very thin.
00:20:12.20 And this patient's vision was reduced to the order of barely being able to see hands moving
00:20:17.11 in front of his face.
00:20:18.26 The contact lens ERG test was... resulted in responses that were unmeasurable, suggesting
00:20:25.15 severe and diffuse widespread photoreceptor degeneration.
00:20:29.20 To give a patient a diagnosis of Bardet-Biedl syndrome
00:20:33.17 requires at least 4 of 6 primary features.
00:20:37.17 These can include rod cone dystrophy, polydactyly on either the ulnar side of the hand or the
00:20:43.22 fibular side of the foot, obesity is a key finding, and often the...
00:20:48.20 based on metabolic indexes, greater than 97%,
00:20:52.08 meaning these patients are quite overweight.
00:20:53.27 Oftentimes, patients will have learning disabilities.
00:20:57.26 General abnormalities can be essential... an essential component of the diagnosis.
00:21:01.25 And in... renal abnormalities such as the cystic kidneys that Wallace mentioned earlier
00:21:05.25 in this talk are a frequent finding in patients with Bardet-Biedl syndrome.
00:21:10.18 Less common features that can also be seen, but which are not required to make a diagnosis
00:21:14.20 of Bardet-Biedl syndrome, include delay in the development of speech,
00:21:19.15 fing... fingers that are not necessarily extra, but might be fused abnormally at birth,
00:21:25.03 similarly, toes that have been fused, or syndactyly,
00:21:28.06 developmental delay or learning difficulties,
00:21:30.22 diabetes insipidus, diabetes mellitus.
00:21:34.03 Abnormalities of the teeth, such as hypodontia, can be a feature of Bardet-Biedl syndrome.
00:21:38.28 Some patients can have problems with their heart or their kidneys.
00:21:42.00 And again, patients sometimes have difficulties with smell.
00:21:46.10 Bardet-Biedl syndrome not only causes rod-cone degeneration, but can also cause...
00:21:52.05 which is variable in its severity... but can also cause pigmentary retinal degeneration with
00:21:56.28 early macular involvement, resulting in very severe vision loss at early ages.
00:22:02.07 And in some cases, the diagnosis is made with a contact lens test, or ERG, as early as infancy
00:22:07.17 or 14 months of age.
00:22:09.04 And these children are sometimes mistaken for patients with Leber congenital amaurosis
00:22:13.12 until a history is taken to find that, indeed the patient has other systemic manifestations,
00:22:19.19 such as polydactyly, or obesity, or developmental delay, or kidney disorders.
00:22:24.00 Many times, a primary care physician has observed these separate systemic abnormalities and
00:22:29.22 not known that the retinal degeneration was associated as well, until the ERG is obtained,
00:22:36.02 at which point a diagnosis of Bardet-Biedl can be made.
00:22:39.00 It's an important diagnosis to make because patients need to be monitored over the course
00:22:43.02 of their life for the development of hepatic, renal... hepatic and renal disease,
00:22:49.09 as well as diabetes.
00:22:51.07 There are up to 14 different mutations that can cause Bardet-Biedl syndrome.
00:22:54.16 And some of them cause very severe and early onset vision loss, with legal blindness in
00:22:59.16 the second or third decade in up to almost three-fourths of patients.
00:23:03.13 However, there are other genetic mutations that cause Bardet-Biedl syndrome which are
00:23:07.14 milder in their onset and severity.
00:23:10.05 Some people can be asyma... asymptomatic and nearly normal.
00:23:14.13 And in this particular mutation, vision doesn't always correlate with age.
00:23:19.00 Some patients retain normal visual acuity until their second and third and even fourth decade.
00:23:25.17 This is an example of a patient with one of the more severe genetic mutations, BBS5.
00:23:31.08 This [unknown] patient was from a family with a history of consanguinity, in that her parents
00:23:37.10 were first cousins.
00:23:38.26 She retained central visual acuity of 20/200, which equates to legal blindness,
00:23:44.20 but does enable her to read large-print letters.
00:23:47.10 But you can see, again, there are retinal pigmentary changes in the macula, which have
00:23:51.25 been seen in other patients with Bardet-Biedl syndrome.
00:23:54.27 In contrast to some of the other patients with retinal degeneration that I showed you today,
00:23:58.22 the optic nerves are less pale, the vessels are less attenuated, and there's less
00:24:03.20 bone spicule pigmentary change in the edges of the retina than are... was observed in
00:24:08.20 some other forms of retinal degeneration.
00:24:10.26 When we get an optical coherence tomography picture of the retina in this patient,
00:24:15.16 we see loss of the inner retinal tissues at the fovea, resulting in her 20/200 visual acuity.
00:24:20.22 But actually, the inner segment-outer segment band, shown here, is relatively well preserved
00:24:25.19 in the macula, again corresponding to the fact that she retained some central visual acuity,
00:24:30.08 even at the age of 20.
00:24:33.17 This is a patient with a less severe form of Bardet-Biedl syndrome caused by a mutation
00:24:38.02 in the BBS1 gene.
00:24:39.26 In this patient we see some abnormality at the level of the macula, and a more extensive
00:24:45.23 evidence of vascular attenuation and pigmentary changes along the arcades.
00:24:51.00 In addition, the disc is slightly more pale in this 19-year-old child with Bar...
00:24:55.09 BBS1 mutations.
00:24:56.16 Her OCT looks very similar to that of the other patient, again, with severe thinning
00:25:00.27 in the center and abnormalities of the connecting cilium bands throughout the macula.
00:25:07.23 So, the take-home points I wish to leave you with in regarding... regarding patients with
00:25:13.07 ciliopathies or ciliary mutations is that cilia account for an important component of
00:25:19.23 photoreceptor structure.
00:25:21.13 So, abnormalities of photoreceptor cilia genes can cause death of the photoreceptors,
00:25:27.09 both the rods and the cones.
00:25:29.08 And abnormalities of photoreceptor cilia genes or ciliopathies are an important cause of
00:25:34.07 retinal degeneration, in addition to multiple other systemic findings that can occur when
00:25:39.05 cilia mutations are present.
00:25:41.28 Again, the widespread expression of ciliary genes often results in systemic abnormalities
00:25:47.08 beyond the eye, including primary ciliary dyskinesia Senior-Loken syndrome,
00:25:53.00 Joubert syndrome, and Bardet-Biedl syndrome.
00:25:56.14 And ciliary gene abnormalities represent an important target, or important targets,
00:26:00.14 for investigation and potential future... future therapies to help patients not only lose their
00:26:05.13 vision due to retinal degeneration but also enjoy healthier and longer lives.

Videos in this Talk

Part 1: Ciliopathies and Retinal Degeneration
Audience:
- Researcher
- Educators of Adv. Undergrad / Grad
Part 2: Ciliopathies and Retinal Degeneration
Audience:
- Researcher
- Educators of Adv. Undergrad / Grad

Speakers: Wallace Marshall, Jacque Duncan

Total Duration: 0:49:43

Recorded: January 2014

All Talks in Human Disease

Talk Overview

Cilia and flagella are complex, but highly conserved, structures found on most cells of the human body. Mutations in proteins localized to cilia can cause a collection of human diseases including renal failure and retinal degeneration. Dr. Marshall begins with an overview of the complex internal structure of cilia and flagella and the machinery, called intraflagellar transport (IFT), required to build and maintain these structures. Mutations in motile cilia were known to cause several human diseases but it wasn’t until scientists began studying IFT in the green algae Chlamydomonas, that the key role of non-motile cilia in human health and development was recognized. Marshall describes how mutations in cilia and basal bodies can cause human diseases as different as renal failure and retinal degeneration.

In the second video, Dr. Duncan explains that the inner segment of photoreceptor cells, where proteins are made, and the outer segment, where light is transduced into a chemical signal, are joined by connecting cilia. Mutations in proteins that localize to the connecting cilia can lead to photoreceptor cell death and vision loss. In a number of syndromic diseases, such as Bardet-Biedl Syndrome, retinal degeneration is just one of several symptoms all of which are caused by mutations in cilia throughout the body. By identifying specific gene mutations causing retinal degeneration, Duncan hopes that better treatments for patients with these syndromes will be developed.

Speaker Bio

Wallace Marshall

Wallace Marshall received his BE in Electrical Engineering and his BS in Biochemistry from SUNY Stony Brook and his PhD in Biochemistry from the University of California, San Francisco. He was a post-doctoral fellow at Yale University. Currently, Marshall is a Professor of Biochemistry and Biophysics at UCSF. His lab is interested in the… Continue Reading

Jacque Duncan

Jacque Duncan is a Professor of Clinical Ophthalmology at the University of California, San Francisco. She uses cutting edge imaging techniques to diagnose diseases of retinal degeneration. Duncan has research funding from numerous sources to develop novel treatments and devices designed to preserve retinal function. Duncan received her MD from UCSF where she completed an… Continue Reading