Canine Ocular Diseases with Dr. Casey Carl, DVM

We're excited to have Dr. Casey Carl, DVM, the Associate Medical Director at Paw Print Genetics, back for another Good Breeder Webinar! This webinar focuses on ocular diseases in dogs. You can also check out Dr. Carl's previous webinar he did on canine coat color genetics here.

Transcript

Dr. Judi Stella [0:02] Hi, everybody! Thanks for joining us today. Today’s guest is Dr. Casey Carl. He’s the Assistant Medical Director at Paw Print Genetics, and he’s going to talk about ocular diseases, including PRA, PLL, and juvenile cataracts. We will have time at the end to answer many of your questions. We probably won’t get to all of them, but we’ll try to get to as many as possible. With that, I will turn it over to Dr. Carl. 

Dr. Casey Carl [0:27] Thanks so much, Dr. Stella! I’m really happy to be here. Thanks for having me again, you guys. I know some of you probably attended my first presentation that I had here with Good Dog. I’d like to thank Good Dog for having me. This has been a lot of fun, and they’re a great team to work with. I’m really happy to be involved with Good Dog and all the great things you guys are doing, so thanks so much for having me. This is great. So today, like Dr. Stella said, we’re going to talk about a variety of different canine eye diseases, for which genetic testing exists. Some of these diseases there are versions of—the diseases for which genetic testing does not yet exist, and hopefully at some point there will be, but we’ll talk about all of those various things. 

[1:10] First of all, we’re going to go over a few different things. We’ve got a few topic outlines here that we would like to discuss. First of all, we’ll go over intro and definitions and some inheritance patterns, specifically recessive, dominant, and X-linked. If you’ve seen my presentations in the past, I often go over some basics, nuts and bolts types of things, before I get started—just so everybody’s on the same page. If some of this is review for you, I apologize. But it’s good to be on the same page and get an idea as to how some of these diseases are inherited. We’re going to talk specifically about Progressive Retinal Atrophy and the wide variety of different types of this disorder that are out there. We’ll talk about Primary Lens Luxation, which is a common disorder that we see in a lot of Terrier breeds. We’ll talk about hereditary or juvenile cataracts. There’s a couple of different mutations that we are aware of that occur across our dog breeds. Lastly, one that wasn’t in the promotional materials for this but that I thought would be a good one to add in here is Collie Eye Anomaly, which is a disorder that’s seen in a host of different herding breeds, and it can be a particular concern in quite a few numbers of breeds. Lastly, we’ll talk about some questions and answers at the end, so save up those questions. If you have anything, we’ll definitely do our best to try to address them.

[02:27] First of all, we’ll talk about some definitions here quickly. The definition of a mutation (or variant in the genetics): it’s an alteration in the DNA that affects gene function. Variants—that terminology is used much more commonly these days than it used to be, rather than mutation—but these variants in DNA can result in a disease or trait if present. Allele is an important word. It’s essentially a version (or one copy) of a gene, so a particular version of  a gene. For example, when we have diseases, we would have a normal copy of the gene that does not contain the mutation or a version of the gene that does contain the mutation. Those are both different alleles. The combination of those two alleles ends up making up what we call our genotype at a particular location. That is just the combination of both of the versions of the gene that a dog got from each parent. (So, one from each parent.) If both of those copies are exactly the same, then we would refer to that dog as homozygous, or having two exact copies (or versions) of the gene (same allele from each parent). Or if they’re different, we would refer to them as heterozygous, so if we’ve got two different copies (two different alleles, one from each parent), then heterozygous is the terminology we would use for different versions. And then lastly phenotype. Phenotype is actually the clinical or physical presentation of the genotype in an individual. Sometimes, if a dog has a particular genotype, they may be simply carriers of a disease, but they may not actually show that specific clinical or physical presentation. We’ll talk about that when it comes to recessive diseases especially. 

[4:06] I’ll briefly go over some of our inheritance patterns that we have here. By far the most common one that we deal with when we’re talking about genetic testing is recessive disease inheritance. But we also can be dealing with some dominant or X-linked inheritance patterns in some of these diseases that we’ll talk about today, so we’ll go over those a little bit as well. 

[4:30] First of all, as a refresher, recessive diseases are those that a dog has to inherit two copies of the specific associated genetic mutation (or one from each parent), so they’d be getting one copy of that mutation from each parent and that would predispose them or place them at risk for that particular disease. Dogs with only a single copy of a recessive genetic mutation—they’re considered carriers of the disease, but they’re not actually going to express it themselves. However, if those carriers are bred with another dog that also carries the same mutation, then we will likely end up producing puppies that have that particular condition or disease. 

[5:07] This is a situation here using our Punnett square. If we took a carrier dog for a particular genetic mutation, we have a carrier here that has one copy of the genetic mutation. This dog here does not have the genetic mutation. This is the ideal situation that we talk about when we’re talking about breeding dogs with a recessive disease mutation. These are handy-dandy Punnett squares, which is something you see in a lot of early biology courses. Basically what we’ve done here is the letters here on the outside of the Punnett square are indicating the versions of the gene that these particular dogs have. For example, here on this carrier dog, the capital A here indicates that this is the normal version of the gene that it got from one of its parents. The lowercase letter down here is indicating a mutated copy of the gene that it got from its parents. What we do here is we essentially pull these letters into the Punnett square in the corresponding rows and columns and get a determination at this one location of the genome what might happen if we bred these two dogs together. If you notice here, we will end up with a situation where we get two of the four dogs have two normal copies of the gene and two of the four dogs have one copy of the mutation down here. Essentially, it’s going to be a 50/50 split between carrier and normal dogs. One way I think about this is that this dog here (this carrier) could pass on either this one or this one to every offspring, so this dog is really the dog that’s creating this 50% scenario here. Sometimes people will think that if they breed a carrier to a normal dog, they’re only going to get 25% but you see here this carrier—it can only pass on one or the other to every dog so it’s really going to be 50% with this. 

[7:00] This scenario here with two carrier dogs is a situation we’re trying to avoid when it comes to diseases. When it comes to traits and recessive traits, then we want to perform this breeding in order to try to get a recessive trait—but when it comes to diseases, this is not going to be an ideal situation. We’ve set up our Punnett square. In this situation, this dog here that was previously normal is also now a carrier. If we extrapolate out all of these allele versions of the gene in the Punnett square, we’ll see this is where we can get into some trouble. Because we’re going to end up with about 25% (or one out of every four dogs) coming up as affected with this particular condition. Another 50% are going to be carriers of the disorder (two out of every four). And then one out of every four (25%) would end up as normal. This sometimes surprises people. People often. Don’t realize that they could actually potentially get clear dogs out of this situation. And sometimes people will test their dogs when they have two carrier breedings and then the normal dog and not understand how that was even possible. It is possible. It’s just not an ideal situation, because some affected dogs are also going to be produced as well. 

[8:05] We move onto dominant disease inheritance. I put a picture of a Bull Mastiff here because it’s one of the few breeds today that we’ll talk about that actually has a dominant risk factor for these diseases, and there is a dominant version of Progressive Retinal Atrophy that occurs in Bull Mastiffs and Mastiffs. But dominant diseases are those where a dog only really needs to inherit one copy of the associated genetic mutation from a single parent in order to develop that disease or increase the risk of the disease, depending on the particular disease. For that reason, we know that at least one of the parents will either be affected with that disease or potentially could be at-risk for the same disease. In some cases, diseases might not always manifest. In some cases, those are going to be diseases that we call incomplete penetrance. We’ll talk about some of those here in a little bit. And then in other cases, the disease may be onset disease, where if genetic testing had not been done, this parent with a dominant mutation—they may not even realize that this dog could develop disease at a later time. 

[9:10] Here we have a similar set-up again with the Punnett square with dominant disease. Here on the left side, we’re showing a dog here that actually has a dominant condition being bred to a normal dog. Again, this dog doesn’t necessarily have to be showing clinical signs, because in most cases, people that had a dog with a dominant disease that was showing clinical signs—most people are not going to breed that dog. But if this has a late onset, or if there happen to be other factors involved, it may be something that could occur. Again, going ahead and taking a look at our Punnett square, we see that roughly about half of the dogs would be normal in this scenario, with a dog with a dominant mutation. Half are going to be either at-risk or affected here for that as well. Obviously, this is a bad scenario that we want to try to avoid in many cases. But we’re going to see a little bit of a nuance to this with a couple of diseases that we talk to today that are technically dominant, but they have significant incomplete penetrance. We’ll talk a little bit about those and how that may change our breeding strategy a little bit. 

[10:15] Lastly, when it comes to the inheritance patterns, we’ve got our X-linked recessive patterns. X-linked diseases are those that are caused specifically by a mutation on the X-chromosome. As you may be familiar, males only have one X-chromosome. Females do have two. But males only have one. They’ve got their X-chromosome, and then they’ve got a Y-chromosome. The unfortunate part for males, though, is that if they happen to get this mutation on their X-chromosome, they don’t have a second X-chromosome to play a role in trying to essentially cover for the other one, or a normal version of the gene to essentially make up for the fact that they have this mutated copy. So, for that reason, males that inherit these mutations are much more likely to develop disease than females, because females actually have to inherit two copies of these, because they have two X-chromosomes. They have to get it from mom and dad, whereas the males really would only need to inherit one copy from their mother in order to actually develop that. 

[11:20] Again, here’s a little bit of a different scenario. We can show our Punnett square again. On the left axis here, we have this dog that is technically a carrier of an X-linked trait. This would be a female. One X version of the X-chromosome is normal; the other version of the X-chromosome, or the other allele, is the diseased version. And then we have a normal male dog up here. He’s got a normal copy of the X-chromosome from one parent and then has its Y-chromosome from the other parent. Again, as we take a look at our Punnett square, we can see where this becomes an issue. We have up here on this left side our females. We know these are female because they have two X-chromosomes here on this side. This dog here—one out of four of them—this female would be a normal female. This female here—50% of females, I should say—would be a carrier in this case. When it comes to the males, though, 50% will be normal (or one out of the two males will be normal) but one of the males (or 50% of the males) will actually develop that disease because they are going to get that mutated copy of the X-chromosome. Again, their Y-chromosome can’t make up for that. They don’t have another version of the same gene there. So we’ll see that when it comes to females, about half will be normal, half will be carriers, but the males, unfortunately: half would be normal but about half of them would be affected with that particular condition. It is important for these diseases that we make sure that these females are not bred to help try to avoid this from happening. 

[13:10] So now we’re going to get to the good stuff! We’re going to get to a disorder known as Progressive Retinal Atrophy. It’s a very widespread disorder throughout the dog world. It’s a close correlate to a disease we see in people known as Retinitus Pigmentosa and can be a very common concern for some breeds.

[13:28] It is a group of inherited eye diseases caused by a variety of different mutations in many, many different genes. There have been dozens of these mutations now—at least a couple dozen, I believe—that are now found. The various PRAs affect many breeds, and unfortunately there are many, many breeds that are known to develop PRA but we actually don’t know the underlying mutation. We do know mutations that are associated with well over a hundred breeds, maybe a couple hundred breeds now. But many PRAs do still exist in breeds out there and the underlying genetics behind those are simply unknown at this time. Again, these PRAs we can test for: recessive, dominant, or X-linked inheritance, depending on the specific genetic mutation. There’s no real universal naming scheme. The early mutations that were found—they tried to stick a little bit more of a universe scheme, but since, things have kind of fallen apart (and we’ll talk about that). The lack of universal naming scheme makes PRA really challenging when you’re trying to determine which specific test your dog might need for a specific breed. Because if you choose the wrong one, it’s not going to be all that helpful for you. We’ll talk a little bit about this naming scheme and how this came about and just a couple of things to highlight in order to make sure you’re getting the right test. These PRA types vary a lot. They can vary in what we call their penetrant (so, how likely a dog with a mutation is going to be to develop the disease). They’re going to vary in age of onset, their speed of the progression of the disease, and the specific inheritance type (as we talked about). And then the various retinal cells—in some cases, with these PRAs (actually in a lot of cases with PRAs)—a specific photo-receptor cell type that exists in the retina there will be affected first. That can change the way that these dogs initially present when they are first seen with this disease. The eye examination findings are essentially indistinguishable, regardless of the type of this particular disease. A doctor may be able to diagnose PRA in a dog but may not be able to tell you which specific form of that PRA. In fact, they would be very unlikely to be able to tell you the specific form of PRA that dog has, if they didn’t know any better in terms of what mutations existed in that particular dog. But testing will help us in determining whether that mutation that is known to occur in that breed is actually the one causing disease. Something that could potentially (at least theoretically) occur is in some cases, you could have other mutations that are not actually known or not tested for. 

[16:04] Just to give you an idea of all of the different types of PRA, I was going to show all the different types of PRA or closely related diseases that we test for at Paw Print Genetics. First we have our Cone-Rod Dystrophies, our Rod-Cone Dysplasias. These are some of the early namings, as I mentioned earlier, that were used. As you can see, they’re a little bit confusing even from the get-go because there was one form of PRA known as Cone-Rod Dystrophy, and then somebody came along and created another form of PRA called Cone-Rod Dystrophy 1 and started from there. So that initially is confusing in and of itself. But some of the more recent mutations that have been discovered—they don’t really apply that name to it any longer. 

[16:46] These are all different genetic mutations that we test for at Paw Print Genetics. Obviously things can be a little tricky, especially if people start using acronyms like CRD for Cone-Rod Dystrophy or RCD for Rod-Cone Dysplasia. Things can get really tricky when you start throwing the acronyms around. It’s pretty easy for people to sometimes get those mixed up. One of the easy ways—at least when you’re trying to find the appropriate testing at Paw Print Genetics—you can actually just do a search for a particular breed and find the list of the tests for your particular breed on our website, to make sure you’re getting the right one. Worst-case scenario, you can also just call into our laboratory and talk to someone, too, and we can give you some advice on how to go there. At Paw Print, we actually have veterinarians and geneticists on staff to talk to our clients daily. You’re more than welcome to give us a ring, and we can chat about that and make sure you’re getting the right one. 

[17:35] So, when we talk about PRA, where exactly is the issue occurring? This is a little graphic here of a human eye. I couldn’t find a canine eye, so there are a couple of changes here that are a little bit different, but we’ll ignore those for the time being because most of this is going to really apply. This is going to be the front of our eye. This is going to be the portion that we see through here on the right. Light is going to come in this way, through our clear cornea at the front of our eye, go through this hole here in the iris known as the pupal. It’s going to go through the lens. The lens plays a very important role in focusing that light to a particular location on the retina here, on the back of the eye, where all this light information is taken and eventually transmitted down the optic nerve to go to the brain. In the case of PRA, the retina is really the site of disease. That’s going to be this thin layer of tissue there that holds all of these (what we call photo-receptor cells or rod and cone cells) back here in this portion of the eye. This retina will start to degenerate. The light will come in and really can’t be taken in in the same way or can’t elicit a response in the same way that it once could. That response ends up not going down the optic nerve and eventually, when enough of these cells are damaged in the retina, then the dog will eventually become blind. 

[18:52] The age of onset can vary greatly. One of the contributing factors to that, when it comes to PRA, is whether the PRA falls into the camp that we would refer to as a dysplasia or if the PRA falls into a camp that we would refer to as a dystrophy. 

[19:08] There are a couple of important things about that. Dysplasia essentially is referred to as an abnormal development of the cells or abnormal development of the retina, in this case. These particular types of PRA are more likely to be seen when there’s a mutation in the gene that’s responsible for the actual development of that cell to reach its normal, mature state. In general, these are going to tend to be earlier onset versions of the disease. That makes sense, because if your genes are mutated and can never develop a normal, mature cell, then those cells would be easily destroyed or purged by the body because they’re not going to be normal enough to be able to make it past some of these “filters” that we have to recognize these types of changes. A good example of this is a type of PRA known as Rod-Cone Dysplasia 2, which we can see in Collies. That is a very early onset disease. Loss of vision begins in these dogs usually around 6-8 weeks of age. Quite often they’re fully blind by about 8 months or so. Dystrophies are a little bit different. A dystrophy type PRAs are caused by a degeneration of normally developed cells. So, the cells will actually reach their mature state, but genetic mutations for these types of diseases quite often occur in genes responsible for the ongoing maintenance of those retinal cells. So, since they can’t be maintained appropriately, eventually at some point, they very well may be destroyed as well or undergo this process of degeneration. In general, this tends to be later onset disorders because the cells actually have to mature to their final state before the degeneration occurs. There are exceptions to this. There are actually exceptions to both dysplasias and dystrophies in terms of the age of onset, but for the most part, this is the general thing that we see. An example of this is Cone-Rod Dystrophy 4, which is a mutation that has been described in a whole host of breeds, but one of the common breeds it’s talked about in is English Springer Spaniel and can be a cause of blindness in the English Springer. This particular disease as well does display some incomplete penetrance, so not every dog that inherits two copies of the mutation associated with Cone-Rod Dystrophy 4 will actually develop the disease, but they may. This disease actually has been reported in dogs anywhere from 1-15 years of age, as the initial age of onset. With this particular form of Cone-Rod Dystrophy, it is quite variable.

[21:45] What would we expect to see if we’re looking at our dogs and they have PRA? What are going to be some of the first signs that we would see? Quite commonly in PRA, dogs will either lose the rods or cones first—either/or, depending on the type of PRA. Which one they lose first will end up resulting in whether they lose nighttime or daytime vision first. When we’re talking about the case of, say, a Rod-Cone type disease (Rod-Cone Dysplasia), the Rod-Cone first indicates that the rods tend to be the specific cell that’s affected in the retina first. They actually tend to be destroyed first. Rods play a really important role in being able to take in low light or to be activated at low light, so therefore when rods are destroyed, night blindness becomes a common thing that we would see, especially in early stages. Dogs may be apprehensive to go into a darker environment from a lighter environment. You may notice that they have a tough time now getting around when the lights get low. In diseases where cones are affected first, we would actually notice the opposite. In situations like Cone-Rod type disease where the cones are affected first (like Cone-Rod Dystrophy 4, like we just talked about), quite often, we’ll notice that day blindness is going to be the first sign we see; they can actually navigate fairly well when light levels are low, but when light levels get high, these cones are responsible for reacting to this very high-intensity light and sending a signal in that case. Those types of stimuli are not going to get through and dogs will have suffered from day blindness. There are disorders where only cone cells are affected. In those dogs, they develop only day blindness in those cases. There are some diseases that can be tested for, just purely cone degeneration only. It can result in that. There is an example in Poodles that is out there. We’re not offering that test at this time at Paw Print, but it is something that is available. There’s another form of PRA known as Central PRA, or it also goes by Retinal Pigment Epithelial Dystrophy (RPED). Lots of fancy words. Basically what happens in these cases is that the superficial pigment that coats the retina—that degenerates and that degeneration ends up resulting in the ability of the retina to process light. It is associated with Vitamin E deficiency, but there are genetic underpinnings for this as well. In dogs that develop Vitamin E deficiency, they may also develop a similar disorder. This one tends to be a little bit more rare in terms of the type of PRA that this one is, but it is something that is seen. Most PRA cases in general end up in complete blindness, but dogs may retain some vision with certain PRA types. It just depends on the specific type and the specific individual. Some dogs will retain at least some vision in these cases. In late onset—I throw this on here; it’s not something that typically is talked about a whole lot when it comes to PRA, but PRA cases as they progress, quite often dogs will end up progressing to late onset cataract formation as well. It ends up not being a huge factor in most of these because the dogs are suffering so significantly from vision deficits usually by this time that it doesn’t end up contributing a whole lot more to the disease state, but it is something that sometimes we can see. 

[25:13] What would we expect to see if a dog comes in, a veterinarian’s doing an examination—what is the veterinarian actually looking for? One of the major things for Progressive Retinal Atrophy would be a change in the size of blood vessels. In Progressive Retinal Atrophy, those blood vessels that they noticed in the retina will gradually decrease in size. There’s also going to be a thinning of the retina that allows us to see some of this more, but it also ends up resulting in increased “eye shine” in these dogs. Tapetum lucidum is the structure that’s in the back of the eye, and if you’re not familiar with the name, you’re probably well familiar with what it does in dogs. One of the ways that this is often noticed is when we take pictures of our dogs and we notice there’s a yellow shine in their eyes when we take a look at the photograph. That’s essentially a reflective surface on the back of the retina that ends up resulting in the light bouncing back. It plays a role in better vision in low-light conditions. The light will actually reflect inside the eye and allow the dog to be able to see a lot better. But in the cases of PRA, with the thinning of that retina, additional light gets to that tapetum lucidum and ends up resulting in an even more pronounced eye shine. Interestingly (and you may be familiar with this), sometimes in cases of dogs that have changes in their pigmentation (for example, merle dogs and other colors), you may notice that they actually end up—instead of having a yellow eye shine, which is common in dogs when that light is bouncing off the tapetum—having a red eye shine, where the light is actually bouncing off of the blood vessels in the eye. That red comes back. Sometimes the pigment in eyes—depending on the breed and depending on what the coat color pattern and things are—we can see some change in the way that that looks. (Just kind of a side note that a lot of people sometimes are interested in.) Dogs with PRA may have no abnormal findings on eye exams until they’re closer to the typical age of onset. This is why annual exams can be so important for a variety of different breeds when it comes to PRA. You do an eye examination very early in the dog’s life, you’re not likely to see a later onset PRA at that time. Many breed clubs recommend doing annual eye exams. This is one of many reasons why that can be really useful, especially if you’re planning on breeding that dog one day. We’re also looking for any inherited eye condition at all that potentially could be a concern, not just the ones you can test for. So eye exams are always really great to consider when we’re talking about the health of our dogs. I look at them as an adjunctive add-on to testing in that they give us more information than genetic testing can give us alone, and we’re looking for diseases that we couldn’t necessarily test for. 

[28:02] Next one we talk about is Primary Lens Luxation. This is a very common disorder that we see in a variety of different breeds.

[28:08] Mostly in Terrier breeds. It’s caused by a mutation in what we refer to as ADAMTS17 gene. It is autosomal dominant, so it only requires one copy of the mutation for these dogs to be at risk, but it does display incomplete penetrance, so that means that not every dog that inherits the copy of this mutation will actually go on to develop this disease. 

[28:30] Here we have the diagram of the eye again. I wanted to show you exactly where we are having our issues when it comes to Primary Lens Luxation. That would be right up here on the lens, but specifically on these little fibers here known as zonules that actually encircle the lens and hold it in place and keep it right here in front of the pupil so that when the light comes in through our cornea and through our pupil, it’s in the correct position that it can transfer that light to the retina in a focused fashion and allow us to be able to see. In the case of Primary Lens Luxation, the mutation ends up resulting in these zonules becoming weaker and more prone to breakage, so these fibers here actually at some point in the dog’s life may break, thus allowing this lens to be able to basically free-float in the eye. The most common thing that we would end up seeing with that, when that occurs, is that that lens will actually pop through the iris and end up what we call the anterior chamber portion of the eye. As a veterinarian, many of us out there have seen this, where a dog comes in and you’re looking in their eyes, and you notice there’s just a lens sitting right in the front of the eye, just hanging out there. This occurs most commonly in this direction, I believe. I’d probably have to double-check on this to be certain of it, but I believe there’s a pressure gradient here that ends up pushing it forward. This is most commonly where it will go. If the lens falls in the back of the eye, it tends not to be as severe of a concern, even though the dog will have blurred vision and not be able to see any longer. When the lens moves forward into this anterior chamber, this can be an emergency. (We’ll talk a little bit more about that in a second, why that happens.) Essentially, when eyes are producing the fluid that fills the eye, it is produced here in the ciliary body. The fluid is emptied into the back of the eye. It squeaks past the lens here and makes its way to the front anterior chamber. This liquid then is drained from the eye through some canals that occur right here on the corner where the cornea meets the iris. These are really important in draining that eye. If this fluid cannot make it through past the lens into the anterior chamber and then drain out, then that fluid begins to build up in the eye. The lens popping into the anterior chamber ends up resulting in that fluid having a much more difficult time being removed from the eye. An increase in pressure will end up in glaucoma in a lot of these cases. So when we have a rupture of the lens, it’s really important for us to get on that quickly so that glaucoma doesn’t set in. That glaucoma can end up doing damage to the optic disc, or the optic nerve here, and end up resulting in blindness in the long-term. So these are often emergency situations. Veterinarians would really want to assess the intraocular pressure in these dogs as soon as they come in to see where they’re at and to see how quickly they need to move on this. 

[31:25] What do we see here? Quite commonly when it comes to Primary Lens Luxation, most of these dogs that have this mutation are going to present with a luxated lens somewhere around 2-8 years of age, but it can vary quite a bit. Sometimes it can be later. I haven’t seen a lot of cases younger than that, but I guess theoretically it could. As I mentioned, the lens dislocates from its normal location because of the breakage of those zonules or ligaments that hold it in place there. Most commonly, us as dog owners are going to notice that all of a sudden, the dog is going to start showing signs of eye irritation. There’d be blinking or squinting. They may be tearing. As I mentioned, the lens can go forward or backward in the eye, but it’s more likely that it will go forward in the anterior chamber. It is a surgical emergency. Try to retain that vision if the intraocular pressure is increasing, that fluid cannot get out. It can end up resulting in glaucoma if untreated. 

[32:22] Both eyes are nearly always affected when it comes to Primary Lens Luxation but there may be a delay in when that occurs. They may be separated by weeks or months, but nearly always if you see one lens luxate in relation to this mutation, the other is probably not too far behind. There’s a particular study that was done here; I’ve actually marked some information down here at the bottom. But this is a study that was done in Tenterfield Terriers and Miniature Bull Terriers, both of which are known to inherit this mutation. They were looking at the penetrance that they saw in dogs that they had tested for this disease, based upon their clinical history. Dogs that inherited two copies of the mutation that’s associated with Primary Lens Luxation, at 2 years of age, none of them were affected. When they tested 3 year olds, they found about 10% of them were affected. When they tested dogs greater than 6 years of age, all 100% of the dogs that they looked at in this particular study had developed Primary Lens Luxation. As I mentioned, this is a dominant disease, though, so it only takes one copy of this mutation to actually be at an increased risk for Primary Lens Luxation. In the dogs they tested that ended up having only a single copy of the mutation, they were at a much lower risk, but it was still a very significant risk of Primary Lens Luxation. Dogs that they had tested that were 3 years old, they had a less than 5% chance. Dogs that were 10 years old had about a 60% chance of having Primary Lens Luxation at that point in their life in this particular study. Now, it is important to note that these are specific breeds and these numbers may vary a lot from breed to breed. We just don’t have a lot of data in individual breeds right now. It could vary quite a bit from breed to breed. Maybe some breeds that only have a single copy are going to be at lesser or greater risk of developing PLL but right now we don’t have a lot of that data. This was informative in terms of what we may see out there. Also, in this particular study, they found that dogs that had one copy of the mutation were more likely to develop PLL at a later age than those that had two copies. There was about an 18-month difference between the two groups in terms of the average age: 54 months for dogs that had two copies and 72 months for those that had one copy. Just making it a little bit more likely to occur earlier in life. 

[34:50] In terms of breeding these dogs, it can be a little bit tricky because many of the breeds that have the mutation associated with Primary Lens Luxation actually inherit it in a very high frequency. When we have a situation like this where the mutation is found in high frequency, we really have to pay attention to the overall genetic diversity of the breed, and that is really crucial for the overall breed health. If we have a breed that has this mutation at a very high frequency and then we go and eliminate every single dog that has this mutation… For example, in a breed that has a 40 or 50% likelihood to carry this mutation, we would devastate the breed by eliminating all of those dogs that would otherwise be a part of the gene pool. So, we have to pay close attention to this. In some cases, especially in breeds where this is at a very high mutation, we may have to consider breeding dogs that have one copy of the mutation to clear dogs in order to prevent all of the loss of that genetic diversity. Now, about half of the dogs in that case would end up being clear from that pairing. The other half would have one copy and would be at an increased risk. That’s counterintuitive, to want to do that, but in the long run when we’re comparing the options here, if we were to eliminate all of the dogs that had the mutation in breeding, we’re going to be undertaking a far worse condition for the breed, because of the fact that they may be much more prone to other issues later. If we eliminate all of these dogs and increase our genetic diversity, when all of these dogs end up breeding again to essentially repopulate that gene pool, all of those dogs are going to be more closely related than they would have otherwise been (prior to eliminating all of those dogs). We know that when dogs are more closely related, within a particular breed, that can result in a host of things, including decreased life span, smaller litter sizes, and (most importantly) an increase in other recessive diseases. Because those dogs that are now closely related are more likely to share some of these common genetic mutations, and so that can increase the risk of recessive diseases—particularly the ones that we can’t test for are the most concerning, because all dogs (or even us, as people) all carry recessive disease mutations that, if we were to have children with the right partner/if a dog was to have puppies with the right partner, then you could end up with a recessive disease that maybe you couldn’t test for that is just kind of hanging out there. So genetic diversity is absolutely crucial. I think this should be an important consideration for all dog breeding, especially in situations like this where it’s a little bit tricky, where dogs that have a single copy of the mutation may actually develop the disease. It may be best practice, though, to prevent dogs who have two copies of the mutation from breeding. I think that that would be relatively wise in most circumstances because all puppies that are born from that (even if they’re bred to a clear dog) would be at an increased risk for PLL because 100% of that litter would end up inheriting one copy of that mutation and would end up potentially having an issue. 

[37:53] Next we’re going to talk a little bit about hereditary cataracts in dogs. There are two known mutations of hereditary cataracts. Oh, first of all though! I put this picture on here. This is my dog, Spike. He absolutely loves sunbathing. In fact, during the summer months, he is actually very familiar with the time of day when the sun will actually hit his pillow on the back porch. Many times, right around that time of day, I’ll find him at the back door waiting for us to let him out so he can go do his sunbathing. Well, one of the causes of cataracts in dogs are environmental factors. One of the major environmental factors is UV light exposure, just like in humans. Older humans are prone to cataracts with age because of chronic UV light exposure and perhaps other environmental things. Dogs also have that same scenario as they age. They may develop cataracts in absence of any genetic mutation just due to that. I have a feeling that someday my dog’s love will end up resulting in cataracts as well, that I may have to deal with that with him at some point in the future.

[38:55] A lot of people do ask about that in terms of inherited versus acquired cataracts. Both are actually quite common in dogs. As I mentioned, when it comes to the hereditary cataracts or juvenile cataracts, there are two known mutations that we deal with. Both of them are in the same gene, this HSF4 gene. One of them is a recessive form of the disease and one of them is a dominant form of the disease. This dominant form of the disease does display some incomplete penetrance as well, like the PLL does. (We’ll talk about this in a little bit.) I have the associated breeds here with these two conditions. I do have some asterisks next to the Poodles here for the recessive HC. This is something that has not previously been talked about much in Poodles or really at all in Poodles. There was one study that found this specific recessive mutation in Standard Poodles. We’ve actually found the mutation in all size Poodles. I don’t have any indication as to where this may have been coming from because it seems a little bit unusual to find in the Poodle, given that it was originally found in the Boston Terrier, the Frenchie, and these Bully breeds. We don’t know at this time, clinically, what this might mean for Poodles. There have been some anecdotal reports of Poodles having a very onset form of hereditary cataracts, which this particular form is, and we’ll talk about it here more in a moment. I just wanted to point that out because people may see this and say, “That doesn’t make any sense. I’ve never heard of this before.” Well, we don’t really fully know if this is going to cause disease in these dogs, but we have an indication to think that it might. It is something that’s listed now on our website for these breeds in case, especially in the case of maybe a dog coming up with an early onset cataract that they could then test this mutation to see if this is an underlying cause of that. (We’ll get into that a little bit more, though, here in a few moments.)

[40:42] Again, our diagram of the eye. I wanted to show what is actually going on. In the case of cataracts, it’s actually the lens that’s involved. This lens, over time, will become more and more cloudy and will start to slowly fill in with all of this opaque protein here that is no longer transparent as it is when it’s properly aligned in there. 

[41:02] That’s because of the abnormal folding and bounding of proteins within that lens that occurs because of these genetic mutations. 

[41:12] Obviously when the light comes in here, if it’s going to be scattered and not focused, then these dogs would end up with a very cloudy field of vision. As this gets more and more severe, they’re essentially blind or functionally blind, even though they can still make out the light; it’s going to be impossible for them to really be able to make out any specific, defined objects. 

[41:33] The lens becomes progressively cloudy or opaque. You can see here in this dog, this actually looks like eye shine in this picture. If you look in there, this is just a very white crystalline-looking object here; that’s the cataract forming in the lens there. This dog is probably not seeing well at all at this particular point. Those look fairly mature here, at least from the outside looking in. The age of onset, the location of where the lens is actually becoming opaque or cloudy, the rate of the progression, and the amount of what we call binocular symmetry (or the amount of similarity in disease in each eye; so if one is cloudy, does the other eye also look the same way?)—all of those things can vary by the specific type of hereditary cataracts that a dog may inherit. When it comes down to it, if you’re trying to figure out “Does my dog have a hereditary cataract?”—if the dog only has a cataract in one eye and it’s been quite some time since that one eye has actually shown the cataract and there’s not a cataract forming in the other eye, most likely that’s not a hereditary cataract. There are exceptions to that, I’m sure, that are out there. But in most cases, hereditary cataracts are going to be seen in both eyes; even if one is affected first, the other one shouldn’t be far behind when it comes to developing that. That is one thing that we often use to differentiate these, especially in cases where there’s no genetic testing for that particular cause of cataracts in breeds, and there are many breeds that develop cataracts at this point for which no genetic testing is available, unfortunately. One of the questions I often will get is do you think this is inherited? If it’s in both eyes, we have to assume in most cases that it probably is. There could definitely be other explanations for why it occurred in both eyes. For instance, some inflammatory diseases or infections that occur in both eyes can cause that. If it only occurs in a single eye, we’re usually pretty safe in saying that it’s probably not inherited. 

[43:33] I’ll first talk about the recessive form of the disease here, quickly. Again, these are the lists of breeds that are most commonly affected. This particular form of hereditary cataracts has a very early onset in dogs, somewhere about 8-12 weeks of age is a very common age for this particular form of hereditary cataracts. It doesn’t explain the late onset cataracts that are seen in Boston Terriers, and so there’s probably another genetic mutation there in Boston Terriers that occurs that causes a later form of this. Dogs with this would be much more likely to be seen early on. They’re usually completely blind by 2-4 years of age with this form. This is kind of a standard recessive mutation, so we would use a standard recessive breeding practices to try to avoid producing affected dogs. Best practice is going to be breeding carriers of the mutation (which are non-symptomatic, because it’s recessive) to clear dogs. You’d get about 50% of the litter in that case that would be clear, 50% that would be carriers. It may be best practice to avoid breeding dogs with two copies of this mutation because, again, every single dog would get one copy of the mutation if this dog with two copies was bred to a clear dog. All of those dogs would have that mutation. You’re essentially increasing the frequency of the mutation in the population by doing that. It may not be best practice to do that. Dogs with two copies, it may be less likely for breeders to breed them for that reason.

[45:02] When we’re talking about the dominant type of cataracts, things are a little bit different, especially with the age of onset because it’s the dominant type of cataracts that we see in the Australian Shepherds and their varieties. They most commonly are seen somewhere between 2-7 years of age in these dogs. As I mentioned, this particular mutation ends up resulting in a dominant form of cataracts, but they do have incomplete penetrance. Dogs with one copy of this particular mutation, it’s only required that they have one copy in order to develop them but some dogs won’t ever develop the cataracts with that. However, dogs that have one copy of the mutation are over 17x more likely to develop bilateral cataracts (cataracts that occur in both eyes). They’re more likely to develop those bilateral cataracts than dogs without the mutation, so greater than 17x more likely to develop that. For example, if your breed had an incidence of cataracts at, say, 1%, the inheritance of this mutation would bring that up to, say, 17%. It’s a pretty great increase in risk when they have that. However, that being said, most dogs that inherit one copy will develop a type of cataract known as a posterior polar subcapsular cataract (PPSC). These particular types of cataracts are not typically going to progress, and they typically don’t interfere with vision. This tends to be a more mild form. However, there are cases where dogs with one copy can develop more severe disease and actually suffer vision impairments, but they tend to be more the exception than the rule when it comes to just a single copy of this mutation. Most dogs with a single copy of this mutation are going to have this other form of cataracts, which tends to be less severe and doesn’t seem to inhibit their vision in most cases. When it comes to two copies of the mutation, we definitely get into a situation where penetrance is much higher. I don’t have great data on the actual percentage of dogs with two copies that will go on to develop severe cataracts in their lifetime, but it seems to be fairly high. These dogs are definitely more likely to develop a severe form of cataracts known as a nuclear type of cataract that actually will obscure the whole lens. It usually will occur in a very rapid progression, and that vision will fade fast when that starts coming on. In terms of breeding recommendations, I went to the ASHGI website, which is the Australian Shepherd Health and Genetics Institute website, and I basically copied this just word-for-word directly from their website as to what they’re recommending. Annual eye exams came up first at the top of the list; monitor these dogs, especially dogs that have a single copy of the mutation, for the potential development of cataracts. Dogs that develop cataracts and are seen on an eye exam—it’s recommended that they should not be bred, regardless of the number of copies that they have. Dogs with just one copy of the HSF4 mutation should be bred only to clear-tested dogs, just like we were talking about earlier. It’s going to be best practice. But, that being said, if that dog with a single copy was found to have developed some cataracts, it would be recommended to not go ahead and breed that dog (even to a clear dog) because of the presence of that. Now this could be tricky, obviously, because if you’re doing annual eye exams, you may find that your dog didn’t develop a cataract by the time the dog is ready to breed but may develop it ongoing. Annual eye exams—they’re not going to prevent that breeding from happening necessarily, but they may end up allowing you to prevent producing more puppies down the line if you happen to catch that your carrier dog (or your dog with one copy) ended up developing these cataracts somewhere along the way. If a dog has two copies of the mutation, it’s their recommendation that it would be better to use a clear or a dog with a single copy of the mutation. It would be better to use one of those dogs, specifically a full sibling since that dog is going to have a very close genetic make-up as to the dog that has two copies (or at least of equal quality). It would be preferable to find a clear or a dog with one copy to breed, rather than a two-copy dog, as I mentioned earlier. If you do happen to breed a dog that has two copies of the mutation, it is absolutely imperative that you breed them to a clear dog to eliminate the number of likely cataract patients. If you breed to another dog that also carries that mutation, it’s going to be at least half of the dogs from that pairing that would end up developing a more severe form of cataracts later. First-step relatives (parents, offspring, full and half siblings) of a clear dog that has been diagnosed with hereditary cataracts (so, if they are a relative of a clear dog that has been diagnosed with cataracts, even though they don’t have that specific mutation) should only be bred to HSF4-clear dogs or those that have no family history of those cataracts. Again, this is a challenge because dogs may not develop cataracts until after breeding age. In most cases, when we talk about a dog with two copies of the mutation, most people know that that’s probably not the best-case scenario to breed that dog. But we fall into a little bit more of a gray area in these dogs that have a single copy of the mutation. It may be that these dogs will develop cataracts with age, but if people start breeding around 2 years of age (which is common), it may not be seen at that particular moment. Doing those annual eye exams is going to be really crucial to try to identify that at the most early point possible to try to limit the potential damage of that in breeding lines. However, I will say many, many, many people that have a single copy of this mutation in their line will end up breeding those dogs to clear dogs. That is a very common practice. It’s not really my place to say whether that’s right or wrong, but it is something that could potentially end up resulting in some of the dogs developing even those mild cataracts; it may make it hard for them to pass an eye examination.

[51:27] And then the last of the diseases we’ll talk about today is Collie Eye Anomaly. Here’s my Spike again, out on the river in Montana, getting a sunbath in—his favorite place to be.

[51:44] This disease is a very common disorder that we see in a host of herding breeds and some other breeds out there. It was originally described in Collies, so that’s why we call it Collie Eye Anomaly. But it’s actually been found in some other breeds now as well. It is autosomal recessive, a pretty straight-forward recessive disease. It’s a disease that’s also known as choroidal hypoplasia, which is actually somewhat of a better name because it actually explains what’s going on. That essentially means an underdeveloped choroid. The choroid is a part of the eye. It’s a layer of tissue that lays between the retina and the white (or the sclera) of the eye. It supplies the retina with nutrients and oxygen, because there’s a whole lot of blood vessels in that layer that end up playing a really important role in supporting the retina and allowing that retina to stay alive. If the choroid is underdeveloped, then the retina may not get all the nutrients and oxygen that it needs and then could end up resulting in that retina undergoing a process of degeneration or not fully developing in the first place, which would be a big concern. 

[52:44] We’re not talking specifically about the retina but a layer under it. For all intents and purposes, it essentially is in the exact same location; it’s just deep to the retina there. Any disorder of the region is going to commonly result in some sort of vision deficiency. 

[53:05] In the case of Collie Eye Anomaly, the clinical signs can vary significantly. Quite a large number of these dogs are actually mild. This disorder is non-progressive, so if a dog is not suffering significantly from this disorder at 3-4 months of age, it’s very unlikely this dog is ever going to have problems with Collie Eye Anomaly. Mild cases may not show any clinical signs. You may not notice that the dog has anything just by looking at them and even in some cases, you may not notice it on an eye exam (which we’ll talk about in a moment). In more severe cases, though, can display obvious bleeding into the eye. They can suffer some retinal detachment, and blindness would usually occur pretty early in life. Blindness, obviously, is the worse-case scenario with Collie Eye Anomaly in these dogs. 

[53:53] The eye exam is an interesting thing that we deal with here when we’re talking about Collie Eye Anomaly. Around 10 weeks of age in dogs, we undergo a development of that tapetum lucidum that we talked about earlier that was responsible for the eye shine, that structure in the back of the eye. And then also the choroid undergoes a process of pigmentation around that same time, 10 weeks of age. Unfortunately, that pigmentation and the development of the tapetum may mask mild disease in these dogs. That results in a phenomenon that is really commonly talked about with Collie Eye Anomaly called the “go normal” effect, which means if you looked at a dog prior to 10 weeks of age when they have these other changes to the eye, you may have been able to easily identify the genetic disease present. But once these changes start going, it may be nearly impossible to actually see any changes in the eye examination. You really want a great clinical understanding of what’s going on with the dog. It really needs to be examined prior to 10 weeks of age. In some cases, with these herding breeds known to develop Collie Eye Anomaly, breeders do that to assess their eyes. If you know that there’s no way that the dogs have two copies of that genetic mutation, then this is going to be less of a concern for you, to get that early eye exam done. But if you know for some reason that your dogs may have it (say it was an accidental breeding or something), that would be a reasonable thing to consider, looking at it early and seeing what’s going on there. 

[55:20] On an eye exam, veterinarians are going to notice certain pale areas of the retina. They may also notice, again, a significant change in the way the blood vessels look, similar to the way we see it in PRA. We’re going to see some decreased or abnormal blood vessels. They can have a very unusual arrangement. This is often found in a portion of the eye known as the temporal region, temporal to the optic nerve. It’s a common location where people would be looking for these particular abnormalities. Also associated with this is the underdevelopment of the optic nerve, or what’s referred to as optic nerve coloboma, or malformation of the optic nerve. This is associated with more severe disease. Dogs that have colobomas are more likely to also suffer from retinal detachments, which can result in blindness. This is something that is more likely to be seen on an eye exam, even after that 10 week period. It’s a lot easier to see this. But not every dog that has CEA actually develops coloboma, so it may not be seen on an eye exam if they don’t develop this, if it’s been after that 10 week mark. 

[56:33] Since this is a recessive disease, carriers of this will not develop the disease and they can be safely bred to clear dogs. About 50% of those dogs from that litter would be carriers but not affected. It may be best practice to avoid breeding dogs with two copies of the mutation to try to keep that mutation frequency lower in the breed population. 

[57:00] That about reaches the end of all the things that I had planned to discuss today, but I’m very happy to stick around for as long as it takes to answer all of these questions that I’m sure many of you have. If I don’t know the answer, I’m also happy to take the opportunity offline to look things up and to get back to any of you as well. You just can’t know it all! I think Dr. Stella has some questions that have been submitted. I’d be happy to start answering some of those. 

Dr. Judi Stella [57:30] Thank you so much. This was great! We do have a few questions. One question that was submitted for the webinar is: Is one color or variety of Poodles more likely to have hereditary cataracts than another color, genetically?

Dr. Casey Carl [57:47] Good question. No, not that I’m aware of. As we did mention earlier, it’s possible that maybe (at least theoretically) some of these Poodles that we see with cataracts may be related to that mutation that was first described in the Boston Terriers. It still remains to be seen, but it is also very possible that there could be other causes of cataracts out there. To my knowledge, there is not a specific coat color that is associated with it. It should be independent, in most cases of cataracts. Unless perhaps there was something to do with the coat color appearance and a particular breed characteristic. In this case, I can’t think of one that would result in that. 

Dr. Judi Stella [58:29] With PRA, does the vision get blurry until everything is indistinguishable or does everything go dark for the dog? They’re wondering if it’s a light darkness thing or if it’s just blurred?

Dr. Casey Carl [58:41] It’s mostly that things go dark. It goes dark gradually over time, but it’s not like in the case of the cataract where everything is just cloudy and they still see the light. With the PRA, basically no message is getting home. As more and more of those cells are impacted, less and less of that signal makes its way to the brain, which ends up making things darker and darker and essentially not able to make out any light at all over time. 

Dr. Judi Stella [59:10] There’s a couple of questions about PLL. One is about how much pain is involved, because you mentioned the intraocular pressure, so is that painful for them? 

Dr. Casey Carl [59:19] Yeah, it can be incredibly painful. Glaucoma is one of the more painful diseases that we deal with, so much so that in situations where the glaucoma can’t be remedied, in some cases, inoculation or removal of the eye is a reasonable option to try to make that dog’s quality of life get better because those dogs are very painful. The initial luxation of the lens probably does have some pain involved, but it’s not going to be nearly as painful as what occurs once that pressure starts building up. 

Dr. Judi Stella [59:58] Is there an immediate action that a general veterinarian can do for the luxation or does that require a specialist? 

Dr. Casey Carl [1:00:05] In most cases, it would require a specialist in order to remove that lens. I don’t know many general practitioners that would be versed enough in that type of procedure to do that. In most cases, an ophthalmologist is going to have to get involved. In the rare circumstances where the lens actually luxates and ends up in the posterior chamber of the eye (in the back portion of the eye) where it can’t be seen easily, in some cases where a person is not able to pay for immediate removal of that lens or those kinds of things, sometimes some veterinarians will take a more casual approach to those and actually kind of just let that be, unless it’s causing the dog some obvious problems. In some cases, they don’t when they’re back there. Again, if it does occur in the front portion of the eye, that would be something that you’d want to get dealt with right away with an ophthalmologist. 

Dr. Judi Stella [1:00:55] Is PRA painful and/or are cataracts painful? 

Dr. Casey Carl [1:01:01] Cataracts are only really painful in the sense that sometimes glaucoma can be a secondary development late in the stage of cataracts, but cataracts in and of themselves are not painful. Many humans get cataracts and, at least the ones I’ve talked to, have never mentioned anything about pain being a component to that. PRA also is not considered a painful disorder either. It’s just kind of a loss of function. 

Dr. Judi Stella [1:01:27] A couple of questions about the color of the eyes. Are blue eyes more prone to cataracts because they’re lighter? 

Dr. Casey Carl [1:01:41] To some degree, yes, because the eyes are less likely to absorb some of that UV light that’s coming in. When we’re talking about juvenile cataracts, that would not be the case. We’re talking about more the old age cataracts. Dogs or humans with blue eyes are more likely to develop cataracts with age if they have that blue eye because of the lack of absorption of a lot of the UV lights; it tends to be more likely to happen. In albino animals and albino people, that becomes even more of a problem where they don’t have any pigmentation in the eye; that becomes a bigger concern. 

Dr. Judi Stella [1:02:17] There’s a lot of questions about specific PRA mutations and also hereditary cataracts for specific breeds, so where’s the best place for people to find if there is a known mutation in their breed? That’s probably the easiest way for me to ask that question.

Dr. Casey Carl [1:02:36] One easy way—at least what a lot of our clients do—is they’ll go to our website and search for a particular breed and the test for that breed. I encourage people, though, to follow up with their breed clubs as well because occasionally there’s a test that we aren’t able to offer for some reason. That would be something that they would have to get elsewhere and may be a really important concern for the breed. One place would be to check simply on these laboratory websites like ours to know whether that is seen in that breed or not. You’re also welcome to call at any time, too, and we can talk about specifics and see. But there are a host of breeds out there—a large number of breeds—which we can see PRA or juvenile cataracts in, and we simply don’t have a mutation yet for it. We’re pretty limited, especially with the cataracts. 

Dr. Judi Stella [1:03:27] Are there any genetic tests for glaucoma? 

Dr. Casey Carl [1:03:31] Yes, there are a few different genetic mutations for glaucoma, and I didn’t cover glaucoma today but there are a few. Quite often they will involve the actual canals out of the eye, allowing the fluid to escape. There’s both what we call an open angle and a closed angle version of glaucoma. There are genetic mutations available for that in different breeds that can be found. We offer a few at Paw Print. 

Dr. Judi Stella [1:04:01] Regarding traits or diseases with incomplete penetrance, is it thought that there’s another unknown/unidentified gene that’s driving the expression or environmental factors or a combination of those things? Why does it just occur in some?

Dr. Casey Carl [1:04:14] All of it is a possibility. Quite often there are genetic mutations that are believed to be implicated in there. There’s a good example of this in degenerative myelopathy. Degenerative myelopathy is a progressive neurological disease. It’s very common in dogs. We see it in well over a hundred breeds now. But there’s recently been a genetic mutation that’s been found in the Pembroke Welsh Corgi, which, if a dog is at risk for DM and they also have this other mutation, they’re more likely to develop it at an earlier age. These kinds of things probably do exist quite commonly in our dogs, but we just haven’t identified all of those yet. As we move forward with more and more understanding of what goes on, we may have more of these modifying factors covered and we may be able to more accurately test for all of these things and be able to make better predictions or better recommendations about how to breed these dogs. 

Dr. Judi Stella [1:05:06] Let’s just do two more since we’re a little over here. When a vet does a normal puppy vet exam, can they see CEA or can only a specialist do that?

Dr. Casey Carl [1:05:19] Many general practitioners might be able to see that if they have the right optimilogical equipment, and if they’re comfortable with really looking in eyes. It does take a little bit more training to get good at looking at eyes and you have to do it a lot. If your veterinarian isn’t quite as well versed in ophthalmology, then a specialist is definitely going to be the way to go. In order to get an actual CERF examination or one of these eye examinations that you can actually register for your breed club, many times that will have to be through an ophthalmologist in order to get that in. That would be a very common route to go. 

Dr. Judi Stella [1:05:57] And then we have one I thought was interesting, sent in before the webinar: The breeder is importing Cavaliers from the UK and EU. They have seen PRA in those lines. Is that something that you test for or have information on?

Dr. Casey Carl [1:06:15] I don’t specifically have that. We hear that quite a bit. There probably is some truth to that in some cases, where a specific line from a particular region of the world ends up coming up with a mutation first. I will say that we live in a pretty global society nowadays and many dogs are bred around the world from different locations. Usually if it’s found in one country, just like we’ve seen with Covid, it doesn’t take too long before all of these things start popping up in other countries as well. I’m not familiar with that being a factor in Cavaliers—just European Cavaliers—but it wouldn’t surprise me that we see that in a breed. It very well may make its way into other countries if it’s not already there. 

Dr. Judi Stella [1:07:01] Okay, well, I think that covers a vast majority of the questions. For anybody that we didn’t get to, you can reach out to us or Dr. Casey and he, I’m sure, would be happy to answer them for you. Thank you so much again for joining us. I really appreciate you taking the time and giving us this information. To all of our breeders that joined us as well, thank you very much. 

Dr. Casey Carl [1:07:23] Thanks so much for having me, you guys. I put up all my contact information here, including my work Facebook page as well. Feel free to go ahead and find me there. I occasionally will post some things. I’m not as active on Facebook as I once was, just due to being a little busier than I used to be, but I’m definitely happy to take any questions here on Facebook. You can reach me there or via email. You can also call our direct line during business hours. I’m very happy to take any calls you have at any time. Thanks so much to Good Dog for inviting me to do this. I’m really, really pleased to be working with you guys. It’s a class-act that you guys have at Good Dog, and you guys are doing great work for breeders. I really look forward to continuing to do more of these as we continue to go forward. Thank you so much. 

Dr. Judi Stella [1:08:05] Thank you! We enjoy working with you just as much! Take care, everybody!