Taysha Gene Therapies, Inc. (TSHA) Earnings Call Transcript & Summary

Good morning, and welcome to Taysha Gene Therapy's CLN1 disease Investor Day. [Operator Instructions] Today, we will be providing an overview of CLN1 disease, review patient natural history data and discuss the TSHA-118 program and clinical development strategy. Joining the call today is RA Session II, Taysha's President, Founder and CEO; Dr. Angela Schulz, our key opinion leader guest speaker from Children's Hospital, University Medical Center Hamburg, Eppendorf; Sharon King, President of Taylor's Tale; Dr. Steven Gray, Associate Professor in the Department of Pediatrics at UT Southwestern and Chief Scientific Officer, Adviser at Taysha; and Dr. Suyash Prasad, Taysha's Chief Medical Officer and Head of R&D. Next slide, please. Before we begin, please note that this presentation will include forward-looking statements within the meaning of the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. These statements may include the expected timing and results of clinical trials for our drug candidates and the regulatory status and market opportunity for those programs as well as Taysha's manufacturing plants. Please see Slide 2 of this slide of the accompanying presentation and Taysha's SEC filings for important risk factors that could cause the company's actual performance and end results to differ materially from those expressed or implied in these forward-looking statements. Taysha undertakes no obligation to revise or update any forward-looking statements to reflect events or circumstances after the date of this conference call except as may be required by applicable securities law. I'd now like to turn the call over to our President, Founder and CEO, RA Session II. RA?

Thank you, Kim. Good morning, and welcome, everyone. At Taysha -- at Taysha, we are developing AAV9 gene therapies to eradicate monogenic diseases of the central nervous system. As you can see here, we have a robust pipeline. And as you can see here, we have a robust pipeline of innovative, potentially -- and potentially disease-modifying therapies. But today, we will focus on CLN1 disease. Next slide. We hope you find this a very informative day and look forward to you joining our future Investor Days on Rett syndrome in September and Angelman syndrome in October. Next slide. Today we are excited to do a deep dive into CLN1 disease, including our preclinical pharmacology and toxicology data and the clinical development strategy for TSHA-118 our promising CLN1 candidate. Currently, there are no approved treatments for this severe and devastating neurodegenerative lysosomal storage disease that is characterized by progressive degeneration of the CNS. We are honored to begin our event with a presentation from key opinion leader, Dr. Angela Schulz, a clinician, and clinical researcher who specializes in lysosomal storage disorders from The University Medical Center Hamburg-Eppendorf. Dr. Schulz will discuss the fundamental aspects of CLN1 disease, review disease prevalence, natural history, patient subtypes and current treatment challenges. Her overview will provide a deep understanding of CLN1 disease and help set the stage for our treatment approach with TSHA-118. Following Dr. Schulz. We are very excited to have a presentation from Sharon King, President of Taylor's Tale, a nonprofit organization supporting CLN1 research and rare disease. Sharon will provide a patient and caregiver perspective on the burden of disease. This perspective will give real-world context to some of the therapeutic endpoints and current management approaches used in the treatment of CLN1 disease as well as provide insight into how even incremental treatment improvements may lead to meaningful benefits in the daily lives of patients and their caregivers. We will then transition into our therapeutic approach for CLN1 disease, with our promising TSHA-118 program, an AAV9 gene replacement therapy designed for lifelong expression of the CLN1 gene. Dr. Steven Gray, Associate Professor in the Department of Pediatrics at UT Southwestern and Chief Scientific Adviser at Taysha, will review the preclinical and pharmacology data generated to date for TSHA-118 and Dr. Suyash Prasad, our Chief Medical Officer and Head of R&D, will discuss the clinical development strategy for this promising product candidate and provide regulatory update. We are very excited about the therapeutic potential of TSHA-118, which has already been granted orphan drug designation, rare pediatric disease designation and fast track designation from the FDA, and orphan drug designation from the EMA for the treatment of CLN1 disease. We expect to initiate a Phase I/II clinical trial for TSHA-118 in the second half of this year, with biomarker data expected in the first half of 2022. With that, I will now turn the call over to Dr. Angela Schulz to provide an overview on the disease and discuss the natural history of CLN1, Dr. Schulz. Next slide.

Thank you for the kind introduction. It is an honor and a big pleasure for me to be part of this Investor Day meeting today and to give you an overview and introduction into CLN1 disease. Next slide. I would like to give you a brief introduction into the institutional I'm working with to give you better feedback on my background. I am the head of the clinic for pediatric degenerative brain diseases. And we mostly see patients with Batten disease or NCL diseases at our center here in Hamburg, Germany. We do have more than 170 patients with Batten disease, both national and international, who come to our clinic every 6 to 12 months. As you can see here with regard to patient numbers, there are large cohorts with patients with CLN2 disease, CLN3 disease, but we also do have a significant numbers of patients with CLN1 disease and all other forms of NCL diseases. We also coordinate an international patient database called the DEM-CHILD database for all NCL diseases. And this allows us to collect natural history data for all our patients that we do see in a very closely prospective basis. And also, it allows us to develop clinical outcome measures for these different NCL forms. We are also a center using the first approved treatment for one of the NCLs, the intraventricular enzyme replacement therapy for CLN2 disease. We do have now more than 50 patients who come every 2 weeks to ask for this kind of treatment. And being part of the Phase I/II trial for development of this treatment and ultimately approval, I think we have learned a lot how natural history data should be used and can be used for clinical trials, especially for pivotal Phase I/II trials. And we hope that this experience will guide us for doing a similar positive development for CLN1 disease. Next slide, please. CLN1 disease is one of many NCL disorders. NCL stands for neuronal ceroid lipofuscinosis. These are new degenerative lysosomal storage disorders and they all have in common that there's lysosomal storage material in almost all tissues of the body. Depending on the various NCL types, the ultra-structure under the electron microscope can vary in these different NCL diseases. And for example, in CLN1 disease, the ultra-structure is resembling a granular structure. This has been used previously for diagnostic purposes, but nowadays, diagnosis is really based on genetic and enzyme activity results. Next slide, please. As I told you, there is a large number of NCL diseases. And in fact, this number has been growing over the past years. To date, we know at least 13 genetically distinct human NCL diseases, and there might be even more out there. 12 of those are autosomal recessively inherited like CLN1 disease. All these NCL diseases share clinical hallmarks, and these are dementia, so loss of psychomotor function, visual loss due to retinopathy and epilepsy. And taken together, the NCL disorders really form the most frequent cause of dementia in young children and teenagers. So this is really a big burden for these patients and taken together, even though these are rare diseases, they really form a fairly large group. Next slide, please. There's a new classification of NCL diseases, and this classification really reflects the different genes and clinical phenotypes. So we do not just talk about an infantile or juvenile NCL disease anymore. We always mentioned the effect of gene and then also, this should be followed by the age of onset when first symptoms occurred and the ages of onset can really range from congenital to infantile, late infantile, juvenile and adult. There is a certain definition congenital means, first, symptoms should start at birth; infantile phenotypes, start at 6 to 24 months of age; late infantile phenotypes, between 2 to 5 years of age; juvenile patients show first symptoms between 5 to 7 years of age; and the late juvenile and adult phenotypes. Next slide, please. Here, you have an overview of all the known 13 different NCL diseases. And you can see that there are different proteins affected in these diseases. The genes that encode for effected proteins can encode both for lysosomal soluble to lysosomal enzymes. They can encode for other enzymes, but also to known enzyme proteins like transmembrane proteins. We focus on CLN1 disease. With CLN1 disease, there's a lysosomal enzyme deficient, which is called palmitoyl-protein thioesterase 1 or in the subsequent slides, I will just call it PPT1. The age of onset in this disease can vary from infantile to late infantile to juvenile to adult patients. And we do see that there is a fairly strong phenotype, genotype relationship. There are certain mutations who clearly cause an infantile phenotype. There are others where we know that they will cause a juvenile or adult phenotype. And we believe that this is most likely due to different amounts of residual enzyme activity. So when we do our laboratory measurements of palmitoyl-protein thioesterase activity, which we can do in our diagnostic lab here in Hamburg, we do see that infantile patients usually really have 0 enzyme activity, whereas in some juvenile or adult patients, we might find low residual enzyme activities. However, still, we do know that even if you only have 50% of enzyme activity, like we can measure in some heterozygous parents, this might be enough to be completely healthy. So in order to restore enzyme activity are most likely does not have to restore 100% or maybe not even 50% of enzyme activity, we believe that far less amount of enzyme might still be enough to be completely healthy. Next slide, please. So as I told you CLN2 disease is caused by deficiency of the lysosomal enzyme PPT1. It's caused by mutations in their respective CLN1 gene. There are more than 70 pathogenic mutations known, and the inheritance is autosomal recessive. In this disease, there's accumulation of lysosomal storage material, which leads to mostly neuronal cell dysfunction and death. The disease is diagnosed by either measuring PPT1 enzyme activity, which can be measured in materials like dry blood spots, leukocytes or fibroblasts. And if they are sufficient or 0 enzyme activity, this is an indication for the disease. And this is usually followed by a genetic detection of the pathogenic mutation on both alleles of CLN1 gene. In some patients, we also do electron microscopy examination of skin biopsies because sometimes the patient might have a sequence variant detected, for example, by exome sequencing on the CLN1 gene, the phenotype might be milder. So we might not be so sure whether or not this is CLN1 disease. So in such case, it's really helpful to find the classic granular deposits in the lysosomes of the skin biopsy. And this is illustrated here on the right lower side, in this image. Also, the fact that we can use dry blood spots in order to diagnose enzyme deficiency in this disease really helps to advance early diagnosis because dry blood spot cards can be easily shipped internationally to our lab and to other laboratories. The enzyme activity measurement is very cost efficient in Germany, it only costs EUR 15 per sample. So we really have achieved improvement of early diagnosis by encouraging pediatric colleagues to really look for this diagnosis early on, and I will tell you about first signs of this disease in the next slide. Next slide, please. Here is an overview on the different phenotypes that we are aware of in CLN1 disease. The phenotypes range from infantile to late infantile, juvenile and adult. Infantile phenotype shows the first symptoms at the ages of 6 to 18 months. And a typical first symptom is psychomotor development delay becoming apparent at the age 12 to 18 months. So these children usually only have a maximum motor function of being able to stand with support. Their maximum language function might be single words only usually if untreated, they might not reach the ability to really form 2, 3-word sentences. At the age of 18 months, rapid cognitive and motor decline happens. By the age of 24 to 30 months or not even 3 years old these children usually are wheel-chair bound already. They suffer from severe muscle hypotonia, ataxia, myoclonus. They have severe epileptic seizures also starting at the age of 2 years. And vision loss another 1 of the 3 hallmark symptoms in NCL diseases, starts not at the very beginning of the disease, however, it becomes apparent at the age of 2 to 3 years. But still, these children are very young and I think the infantile phenotype really reflects very well the record rate of progression in this disease. The next phenotypes that we are aware with late-infantile phenotype starting at 18 months to 4 years. Here, first symptom is not a delay, but epilepsy and psychomotor decline already. So these children might develop normally at the very beginning, but then at 2 to 4 years, seizures start happening in parallel, there is rapid cognitive and motor decline, and then this is followed at the age of 4 to 6 years by vision loss. So still rapidly progressive with this type of disease, but starting slightly later. The juvenile phenotype starts at the age of 4 years and can start even up to early adolescence. And here, the first symptom is very different from the other 2 phenotypes, it's vision loss. These children have a completely normal psychomotor development until the age of 8 to 12 years. They go to school. They are very bright. They even have good grades in school. However then, vision loss starts at the age of 6 to 10 years, but still, they might be cognitive or completely normal. However, at 8 to 12 years, early teenage ages the cognitive decline starts happening followed by epileptic seizures and motor decline. But overall, this disease progression is slower compared to infantile late infantile and the order of symptoms is different because we have vision loss as the first and not as one of the last symptoms. Very rare phenotype that exists as well is the adult phenotype, which starts in late adolescence or older. The rate of progression is very protected and the first symptom can vary. It can be cognitive decline, psychiatric problems, depression, vision loss, motor problems. There are very few case reports. And in these case reports these patients range from having 2 to 3% of residual enzyme activity only. Next slide, please. So I think this overview has shown you that CLN1 disease phenotypes can vary by age of onset, order of symptom onset, rate of disease progression and life expectancy. The infantile and the juvenile phenotypes really are the most prevalent ones to our knowledge today. So in Germany, for example, and in other Northern European countries, the infantile phenotype is quite prevalent. We also do have juvenile phenotypes, similar condition might be in the U.K. In the U.S. also, I think they're mostly infantile and juvenile phenotype patients. There is a strong genotype phenotype correlation for CLN1 mutation. For example, infantile CLN1 patients in Finland, all have the same mutation. Next slide, please. This is just a graphic overview on focusing on these 2 different phenotypes, just again, to really emphasize that they are very different and that the rate of progression is very different and also the order of symptom onset is different. Juvenile phenotype, first symptom vision loss at the 10 to 12, followed by the psychomotor decline, children are blind in their late teenage ages then this is followed by seizures, epilepsy, might be very therapy resistant and then in the early 20s, these children are wheelchair bound, and the age of death might be in the early or late 30s. Infantile phenotype, everything is happening much, much earlier. These children do not have a normal psychomotor development. They do have a delay in their development earlier on and already show their first signs of psychomotor decline at the age of 1 to 2 years. Already by age 2, 2.5, they will shut down, they suffer from very therapy refractory seizures and turn blind. The age of death might vary a bit also depending on different palliative care measures. But I think this graphic really shows you that in case we are able to have a phenotype altering treatment. And we truly hope to have this in our hands very soon with the help of Taysha, we should be able to see any success and stabilization of disease progression very soon in infantile patients. And also, we have the great condition that juvenile phenotype patients who have a normal psychomotor development at the beginning until early school age are also patients who can be very well followed because they can undergo neurocognitive testing, they can do a lot of different prospective clinical scoring assessments. So we do have 2 scenarios that allow us very well to test efficacy of putative treatment. Next slide. In order to not only talk about this disease, but give you a little bit of an idea of what the disease looks like in a child, I would like to share with you a series of videos that a mother of a boy with CLN1 disease was kind enough to share with us here. This is the same boy at different ages. So if we start the first video at age 12 months, you see that this little boy already has delay in his psychomotor development. He's not able to stand with support. However, he's very alert, he has very active movement. He does voluntary movement. So there is a delay, but we do not see regression yet. Next video, please. At the age of 18 months already, he is wheelchair bound. So now we do see the effect of psychomotor regression already. You see that his alertness has decreased. He is a little bit more fuzzy and he will not be able to sit without support anymore. Next video, please. This is the same boy here at the age of 2 years or 6 months later, where seizures have become a big problem. You can see here that he has partial seizures during his sleep with the twitching of his face. Next video, please. At age 3 years, the disease has significantly progressed. The boy is now completely bedridden, suffering from dystonia from myoclonus. He has swallowing difficulties. And this is really a stage of the disease, which is extremely burdensome, where agitation, irritability, really cause a big burden to the family and especially to the patient. Next slide, please. This is the same patient at age 5 years. Here, he is in our intensive care unit. He has suffered from severe pneumonia. But fortunately, he was able to recover from that. And so you see him on the last video at age 6 years, being in the late stage of disease, but we're happy to say in a quite stable stage of the disease. He is bedridden but he doesn't suffer from dystonia. He's quite relaxed. You might be able to see his smile and he's enjoying to listen to his mother's voice. So here you see him smiling. So the disease in late stage disease kind of, we call it burns out. So some of the problems we see earlier on get milder, but still, of course, it's a progressive disease, and these children have to suffer severely. Next slide, please. And one of the worst symptoms if you can say that there are any worse symptoms in this disease because everything is really terrifying is the symptom of what we call agitational distress in these infantile CLN1 disease patients, where we do see a lot of movement, spasticity, ophistotonus, dystonia, these children cry, scream, whimper, they show tachycardia, sweating. This is a very complex clinical picture which might be suggestive to pain, but we have been able to rule out pain in quite a few of these children and we're able to calm then down with the right neurologic medications, which help them to calm down, but not necessarily pain medications. So it's important to be quite experienced with this disease in order to be able to distinguish the symptom of agitation and distress from pain because, of course, these kids could also have various reasons for pain. But however, if we could already improve this phase of the disease with the severe agitation I think we would help these children a lot. And just to give you an idea what this could look like and that's the video on the right side, there's a lot boy, he is I think 14, 15 months old at that age, and he has been crying and screaming for hours and hours during the day and at night. So this is really terrible for patients and parents. And this is the phase of the disease that is very distressful. Next slide, please. So why is this happening? Well, we have told you already that CLN1 disease is a neurodegenerative disease. And the infantile form of it is very, very rapidly progressive. And this is reflected by severe brain atrophy, as you can see here on the MRI image in the middle. You can also see the severe brain atrophy on the right side. This is a post-modern brain of infantile CLN1 patient. And also, the severe loss of cortical gray matter is reflected by the EEG, which is basically almost no activity. It's almost a flat line EEG. So this really reflects the rapid progression of neurodegeneration. Next slide, please. Now switching over to the other second most prevalent form of CLN1 disease is the juvenile form. I told you already that these children show normal second order development until ages 8 to 12 years. So nobody would think about this disease before that age. But then at early school age, usually Grade 1 or 2, the children start to show symptom that we call overlooking. So they do not focus anymore where they want to look, but they use their outer retinal segments in order to be able to focus on something. This is usually becoming apparent at the age of 6 to 10 years. If you look at the retina, we do see signs of retinitis pigmentosa and also stemming of the arteries and venous vessels on the retina. The vision loss is followed by cognitive decline then epileptic seizures and then motor decline. And the motor decline is often really represented by Parkinson like movement disorder, and we can show you this on the video here on the right side. This is a young lady, she's 18 years old, and she shows these short steps, bend knees that is very typical for a Parkinson like movement disorder, very similar to Parkinson patients. Next slide, please. Here, we see what is going on in these patients' brain, also in juvenile CLN1 disease. There's progressive brain atrophy, here is an MRI of the same patient at age 11 years and 18 years. There's significant loss of cortical gray matter, but it's not as rapidly progressive as we've seen it in infantile CLN1 disease. Next slide, please. So what are the challenges with CLN1 disease, if we want to go and develop a clinical trial design and endpoints. Of course, there is a limited number of patients. This is a rare disease, but we're very confident that this challenge can be overcome. Next slide, please. This is the main reason why we have started years ago the so-called DEM-CHILD NCL Database Consortium where 19 countries and 26 centers are collaborating in collecting natural history data on various forms of NCL diseases. This started initially as a European project because it was funded by the European Commission. However, now it has spread to various countries, including the U.S., Southern America, Asia and we're very happy to have this great collaboration with our colleagues all over the world. Next slide, please. This international collaboration really has the aim to collect precise natural history data of all types of NCLs to also improve early diagnosis because if you want to go into clinical trials, we need to diagnose these children early on. We want to optimize standard of care for patients so that we're really able to compare disease progression among them under same treatment, and we want to establish evaluation tools for experimental therapies. And most importantly, these data should be available to any third-party be it scientists or industry in a very transparently regulated and time effective process. Next slide, please. So the database characteristics are really in line with what those FDA and EMA really ask for in order to acknowledge this as control data in clinical trial. The database has been audited and approved both by EMA and FDA when we collected and used CLN2 disease natural history data in this database as control data for Phase I/II clinical trials for CLN2 disease. So they were happy to see the type of data collected, the audit trail, the data storage on different servers with emergency power supply and the fact that we do have a backup of every data set every 24 hours. And in addition, we have independent data monitoring and the data collection is in compliance, both with international and also with a quite strict European data safety and protection rules. Next slide, please. This international collaboration is quite successful, should be reflected by this table here. If we take together all our patients with CLN1 disease here from Italy, Finland, Germany and the U.S., we have a total of 61 CLN1 patients. 39 of those having infantile phenotype, 16 with variant late infantile and 6 with juvenile. And the number is constantly growing. This is a data cut from about almost 3 years ago, where we collaborated and we did the first analysis of these data. Next slide, please. But not only do we need a good number of patients, we also need good reliable clinical outcome measures and biomarkers in order to test treatment efficacy. Next slide, please. We do have the great situation that there are already quite a few approved clinical scoring systems for NCL diseases. We do have a clinical score for late infantile and juvenile CLN1 disease that we call the Hamburg scale. It has already been applied to CLN2 disease and was used as a control measure for a Phase I/II pivotal trial for CLN2 disease. And this scale has 4 functional categories, motor function, language, visual function and seizures, and each function is scored from normal function to no function left being 3 down to 0. This is a very easy-to-use scale. There is excellent inter-rater reliability, and it has the advantage that you can use the scale both retrospectively and prospectively. So we are able to assess the entire disease course longitudinally. We can do retrospective analysis prior to date of diagnosis. And then at our center, we start the prospective collection of data after diagnosis of the patients when they regularly come to our clinic every 6 months. The focus is really on functional relevant outcome measures. And however, for the infantile CLN1 phenotype, we do need some adoption and selection of parameters, which I will show you in a moment. On the right lower side, you see a graph illustrating disease progression in 41 CLN2 patients where we were able to assess their disease progression over the entire course of the disease and they lose on average 1.8 scoring units per year. And you can see that using this scoring system, we have a very homogenous disease phenotype with regard to the loss of motor and language function. Next slide, please. There's another rating scale developed by the University of Rochester, Professor Jonathan Mink, which is the Unified Batten Disease Rating Scale. This rating scale is really very well developed for the juvenile phenotype of CLN1 disease. This rating scale is much more detailed compared to the Hamburg scale. So teaching is quite important in order to ensure a good inter-rater reliability and it can only be used prospectively. But when using prospectively, it gives you a very detailed description of the juvenile phenotype. But also this scale needs some adoption or selection of parameters for the infantile NCL phenotype. That good teaching really results in very good inter-rater reliability shows you the slide on the right side, where we have performed Rater training back Jonathan Mink here at our Hamburg Center, where 4 of our team -- 4 NCL physicians have been trained and have rated a number of patients simultaneously, and we do see that there is the agreement between each rater and trainer, was more than 99%. Next slide, please. In order to overcome the challenges that we do have with the original Hamburg scale and the UBDRS scale in the infantile NCL patients, we really have the challenge that most children who were affected at this early age do not reach milestones to walk without support, and they will not be able to talk in short sentences. But no scoring systems that we have used for the older children have used these milestones, and therefore, they can only be used with some restrictions. So we're very happy that our patient associations like Haley's Heroes support us in order to develop the Hamburg infantile CLN1 score. Next slide, please. This score looks very much like the other Hamburg scores. However, here, we have another category where we look at the age appropriate function and where we ask whether there's development delay presence. So we do not only look at normal function down to no function left, but we do look at delay of function and age appropriate function. And the categories we focus on our mobility, fine motor function and expressive language because these are the ones that we can really assess over time. We also have selected a couple of add-on categories like digital attention, the agitation irritability, which I mentioned before, seizures, feeding, communication and interaction where we look at whether patients are age appropriate or whether there is some pathology. This, again, is a very easy-to-use scale, so it's easy to have good inter-rater reliability. Again, we can use it retrospective and prospectively, which I think in infantile NCL is very important because by the time children are diagnosed, they might already show developmental delay. And again, we focus on functional relevant outcomes. Next slide, please. We do have 16 infantile CLN1 patients that we are applying the scoring system, we're about to publish these data. This is just a few patients that we show here, there are 2 patients where we have accessed the total score. But also on the right upper side, you can see the score for mobility, lower left side fine motor function, lower right side, expressive motor function, what these data already indicate that we have a very rapid disease progression. So these children lose scoring units rapidly, and they do so in a very homogeneous fashion. So the way these curves look like, really remind us to what we've already seen in late infantile CLN2 disease, where we also had a very rapid homogeneous progression of disease, and these data at the time really helped us to have good control data for clinical trends. Next slide, please. So use of natural history control data in clinical trials, can this be done? And especially, can it be done when this data have been collected independently or previously to starting the clinical trial. Next slide, please. And I believe that this is really possible, and I think we were able to show this. Again, this is the example from CLN2 disease. These are 41 CLN2 patients who we have rated over the entire course of the disease for their motor and language score, and we were able to calculate their rate of decline, which was equivalent to the loss of 1.8 scoring units per year. And these natural history data were used as comparative control data in a Phase I/II clinical trial, they were collected independently, they were successfully audited by FDA and EMA. They were collected in international collaboration, and there was a nonexclusive data transfer at that time to the sponsor BioMarin. Next slide, please. And here is the result from the respective clinical trial where we compared patients treated with an enzyme replacement treated with treatment with cerliponase alfa in CLN2 disease compared to untreated natural history patients over time. The red curve are the untreated patients and the blue curve for the treated patients, and you see the change of the motor and language score over time. So the more the score decreases and becomes negative, there were several children doing, and we could show that there was a significant difference between treated and untreated children. Next slide, please. So we do think that especially in these rapidly-progressive diseases, such natural history data can be well used in clinical trials and a good tool to show efficacy of new experimental treatments. Next slide, please. And starting early on with the collection of these data can really advance and accelerate the approval of new drugs for these terrifying diseases. We were able to really speed up the development of cerliponase alfa for CLN2 disease as we can see here. We have already done a lot with regard to collecting natural history data for CLN1 disease. Next slide, please. And we hope that these efforts that not only take place in our center, but also at the University of Rochester, at various other places in Europe and in the U.S. and really, with the strong dedication of many international researchers to share their data, to share with third parties like Taysha can help accelerate the development of clinical trials and ultimately, drug approval for a disease like CLN1 disease because it's a terrible disease. There are many children suffering from it and the time is running, and we really need to make a change. I thank you for your attention. Next slide, please, also happy to take any questions and look forward to the next talks from my colleagues. Thank you.

Thank you, Dr. Schulz. We will now begin the Q&A session. The first question comes from Joon Lee of Truist. Evidently, PPT1 is expressed in non-CNS tissues. What are some of the non-CNS manifestations of the disease and with systemic administration of gene therapy be considered?

Well, that's a very good question. So far, we do not have a lot of evidence that other organs are affected by the disease. And we do not really understand why this is the case. I think one reason why we do not see other problems really is the rapid progression of the disease and if patients would get older, they might show other systems being affected. The only thing that we might see in very few patients is some ventricular hypertrophy, so some cardiac pathology in the juvenile phenotype. However, in infantile patients, late infantile and most juvenile patients, I haven't seen any other organs being affected. However, we should be aware of the fact that other lysosomal storage disease is like mucopolysaccharidosis where it well affect not only the CNS but other organs. So we should really monitor the entire body system very closely if we are able to change the course of the disease and have the children become older.

Great. And a follow-up question from Joon Lee of Truist. In your view, which group infantile or juvenile have a better chance of showing improvement with gene therapy?

Well, first of all, I think what we are aiming for really is stopping progression and slowing down progression, we cannot turn back the wheel with regards to improvement. There are 2 challenges. So in infantile patients, I think we have a condition where the disease progresses very, very rapidly. So if we would be able to change the course of the disease, we should be able to see this in a very short time. And if I compare this to my experience with late infantile CLN2 disease, we were able to show efficacy of treatment within 1 year of treatment. And these data were used then for the approval of the medication. And late infantile CLN2 disease progresses slightly slower than infantile CLN1 disease. So we have a rapidly progressive disease where if we have a good effect of treatment, we should be able to see this very, very early within a year, maybe even earlier, I would say. However, we are dealing with patients who are very, very young, who might have some psychomotor delay. So there is a challenge in doing certain tests on them. It's a challenge under neurocognitive testing, et cetera. However, in the juvenile CLN1 phenotype, we do have patients who are normally developed initially where we are able to do those tests. However, for these children, it might take a bit longer in order to see efficacy of treatment because the overall disease progression is more slow. So I think we can learn important things from both patient groups.

Your next question comes from Kristen Kluska of Cantor Fitzgerald. Dr. Schulz, given you see a high number of CLN2 patients, do you see any overlaps on phenotypes with natural history and patient progression with CLN1 as both our soluble lysosomal enzymes and vary in terms of age onset?

Yes. We do see some overlap, which is why in our diagnostic laboratory, we have a routine that every patient where somebody asks for CLN2 diagnosis, we automatically also measure the deficient enzyme for CLN1 disease, PPT1 because we want to make sure that we diagnose both diseases really early on because there is indeed some overlap. But using enzyme activity assays and genetic testing, I think we're able to clearly diagnose each variant. But I think since the availability of an approved medication for CLN2 disease, the awareness of NCL diseases, CLN2 disease of enzyme activity testing really has increased significantly. So the number of CLN1 patients that we diagnose has increased tremendously over the last 3 years.

Thank you very much. Your next question comes from Yun Zhong of BTIG. Do patients with the adult form have a normal lifespan? The 2% to 3% of normal enzyme activity in patients with adult form, is it measured from the plasma? And what do you think could be the minimal enzyme activity from gene therapy that could bring clinical benefit to patients?

These are great questions, but they are all quite hard to answer, I think, at this stage. We do not have enough data to really make clear statements about life expectancy in adult patients. I mean the adult patients that I follow, I follow them since about 15 years. So they might now be in their late 40s. So there's still some time until we would be able to tell whether they do have a normal life expectancy. I think it's just too early on with -- since the disease has been diagnosed the first time since we had the first adult patients in order to have such data. So it's hard to tell at this moment, but it could be that they have a normal life expectancy, but I'm not sure about this because, again, we're waiting on other organ manifestations and are wondering about that. With regards to residual enzyme activity, I think we need more data on this, and we are in the process of getting more data. What I can say is that, for example, in CLN2 disease, when we test heterozygous parents, they only have sometimes 40% of enzyme activity from what we do see with regard to reference ranges in normal healthy adults, but heterozygous parents are completely healthy, completely normal. We know from other lysosomal storage diseases that sometimes 5%, 10% of enzyme activity can be enough in order to be completely healthy. So I think restoring 100% of enzyme activity is not necessary, not even 40% might be necessary. Probably you only need much less than that. But I think these are data. We still need to learn more about and collect more in patients. And it's important to really do this in the same specimens, so whether it be leucocyte or dry black spots or CSF and do this with the same laboratory method, but this is something that's ongoing work.

Right. Thank you. Your next question comes from Kristen Kluska of Cantor Fitzgerald. Along similar lines of the prior question. What percentage do you think of enzyme activity is needed to show an impact on some key manifestations? And do you think this differs in respect to the different phenotypes?

I don't think that this might differ with respect to different phenotypes. Of course, if you have a milder phenotype, we might already have some residual enzyme activity within the patients. So you don't need to add that much. But in the end, they might all need the same final amount of enzyme activity. But as I said earlier, this for me with regard to human data, this is hard to guess, but maybe my colleague, Steve Gray might be better able to answer this with regards to data from the animal models.

Great. Thank you. Your next question comes from Laura Chico of Wedbush. Dr. Schulz, thank you so much for showing in depth the symptom burden and progression of CLN1 patients. Given your experience with Brineura, I'm wondering if you could elaborate on what would be a good outcome for gene therapy in these patients, and what aspects of the disease are most important?

Well, I think this might depend a little bit on the phenotype we're looking at. But in general, I would say that looking at motor function, looking at language function in the infantile phenotype, looking at the symptom of irritability would be good functional categories of the disease where we should be able to see stop of disease progression or slowing down of disease progression. Looking at the category of seizures, this is a little bit more challenging because seizures can be affected by different anticonvulsive treatments that the children are on and we usually see sometimes improvement or worsening of seizures over the course of the disease, really depending on what medications they are on. So this is something that's a little bit more flexible. But I think motor and language function and in case such treatment would also be applied to the eye, of course, vision function would also be not their outcomes.

Great. Thank you. Your next question comes from Silvan Tuerkcan of JMP Securities. Within the CLN1 disease scale, which measures do you expect to be impacted first and most by a functioning gene therapy?

I would think the physical categories with regard to motor function and language function.

Great. Thank you very much. This now concludes our Q&A session. Thank you, Dr. Schulz for all your insights and for addressing all these questions.

It's been a pleasure. Thank you.

I would now like to turn the call over to Ms. Sharon King who will discuss the disease burden and patient -- from a patient and family perspective. Sharon?

Thank you, and good morning. Thank you, Taysha, for inviting me to share a little of my family's experience with CLN1 disease. As you've heard from Dr. Schulz, CLN1 disease is a devastating illness for the child and for the family. There are medications and therapies that can help to alleviate some of the symptoms. But for now, there's nothing that gets to the underlying cause of the disease. These children and families need and deserve better outcomes. Next slide, please. My daughter Taylor was diagnosed with CLN1 disease in 2006. And just before her eighth birthday and she passed away in 2018, just after her 20th birthday. I often think of Taylor before Batten disease entered our lives, a time when her life held so much promise. What would she be doing today, which is a woman of 23. Would she be in graduate school, would she be starting her first job, would she be in love. From the beginning, Taylor loved life. She was happy. She was precocious. She was whip-smart, and she could hold her own with her older sister and brother. She wanted to be a vet and the pop star and she worked at it. Her family sat through more performances from the heart in our family room than we can count. Taylor could sing word for word, many of her favorite Hannah Montana and high school musical songs. She was an extrovert in a family of introverts, and she changed us forever. She made us better. And I believe Taylor made the world better. And I think she's going to continue that legacy for a long time to come. Our focus after Taylor's diagnosis was to find joy in each day. but there were many days when finding joy was much like running a marathon. Other days are really race. We depended on members of our team, Taylor, to help us find reasons to smile and say, today is a good day. And in the final days of Taylor's illness, I made a promise to continue the fight for others. And I also promised not to forget or sugar coat the hardships that these children and family face. We can't make things better if we don't understand the experiences and the challenges faced by these children and families. Next slide, please. I sometimes wonder why it wasn't apparent to me that something was seriously wrong when I think about the symptoms that led to Taylor's diagnosis. It was insidious happening over the course of about 2 years. At the time, I didn't string any of it together, but as I look back, I can now see the path to a tragedy. Taylor was reading when she entered kindergarten. So I wonder why I wasn't more concerned when here first grade teacher came to me to report Taylor's DIBELS scores. DIBELS scores give the teacher information regarding the child's potential for reading success. Taylor's low scores were totally unexpected, a backwards progression. And I wish that I've been more curious at that time. But that's the point. The scores were totally unexpected. We asked for a retest and the scores improved. So we chalked it up to a fluke and didn't think about it again. But in October of Taylor's second grade year, we visited the North Carolina State Fair with my parents. My mother, my older daughter, Laura and Taylor visited an exhibit where you have to exit by going up dimly lit stairs. Mom and Laura noticed Taylor feeling for each step with her toes. It was obvious. She couldn't see. So mom made a point to tell me and encourage a doctor's visit. I didn't follow through until I saw the problem for myself. Few weeks later, while trick-or-treating Taylor was falling up and down porch steps and over plants and bushes. She was either extremely clumsy or she couldn't see. I called in the first available appointment, was in January. So 2.5 months later, she was examined by a pediatric ophthalmologist. He could find no evidence of vision loss. He did think the Taylor had an emotional issue. He said he thought she was looking for attention. And I left the appointment frustrated and angry because Taylor was not my first child. And I thought she was very happy and well adjusted. But a month later, her teacher came to me and said that Taylor was not attentive in class, and she was certainly not meeting expectations in the classroom. She suggested an evaluation with the schools counselor, and we agreed. A month later, the school's counselor came back to me and said, there is something going on with Taylor, but I just don't know what. And privately, she said to me that she thought whatever was going on with Taylor was going to need more than the school could offer, and we were going to need outside help. By this time, I was really beginning to worry because our happy child was becoming more and more withdrawn. I made 2 appointments, the first to a learning specialist and then to a pediatric neurologist. The learning specialist diagnosed a nonverbal learning disability. The neurologists treated for ADHD but the medications seem to make things worse. In the meantime, we decided to get to the bottom of Taylor's vision issues, and we made an appointment with a neuro-ophthalmologist. We saw him multiple times and I always thought there was something in his domain that made me suspect he suspected more. He also brought in a retinal specialist who confirmed retinitis pigmentosa. Again, I felt uneasy because I suspect both doctors thought something more was going on than vision loss. A week later, the urologist called and asked me to schedule genetic screening for Taylor. And I resisted because Laura's wedding was 2 weeks away. She absolutely insisted. We get it done and get it done quickly. So we went for the blood draw just before the wedding. We would later learn that Taylor's neurologists had diagnosed another child in our area with CLN3 disease, a form of Batten similar to Taylor's CLN1 disease later onset phenotype just a few months prior. Imagine a rare disease like Batten and a neurologist sees it twice within a few months. Laura had only been home from her honeymoon a few weeks when the geneticist called and asked that we come in to review Taylor's results. We scheduled a visit for the next day, July 24, 2006, diagnosis day CLN1 disease. Next slide, please. We were hit by a title wave of grief. And it's a grief that turned you upside down and inside out. It doesn't go away. You just learn to live with it. It's not a grief solely owned by the parents. It affects the family, the extended family and even friends. On diagnosis day, we all became sick. In those first weeks, life was uncertain, and we cried a lot. We couldn't plan a future because we could barely get through a day. Close friends rallied and the diagnosis was so frightening. Others didn't know what to say. So they avoided us. We didn't tell Taylor the extent of the illness only that she would be seeing a lot of doctors, and she was going to have to help us to help her. What else could we do? She was barely 8 years old. And we didn't want to destroy her hopes and dreams. She was smart enough to know that something was going on. But as a family, we believe that hope is important. For Taylor, it was a blissful kind of hope. And for her family, it was more of a pragmatic hope. We needed to believe in the possibility of a different outcome than that shared by the geneticist. And we founded Taylor's Tale to give that hope wings. This little public charity gave my family and friends a way to fight back and channel grief productively. For a long time, Taylor's vision loss and learning difficulties were really the worst effects of CLN1 disease. But in the beginning, and in the beginning, her diagnosis caused more problems than the disease itself. As Gemini had experienced some isolation after her diagnosis, so did Taylor. Parents were afraid to invite her over for play dates. What if she failed, what if she had a seizure. The isolation began almost immediately out of uneducated fear. The school system also faced Taylor's diagnosis with fear and trepidation. Instead of looking at the whole child and focusing on what she could do they focused on what she struggled to do or couldn't do. And at some level, I understood this turmoil because remember, they were dealing with not one Batten diagnosis but two, IEP meetings went on for hours with multiple attorneys in the room. But we wanted to spend more time with Taylor and more time fighting Batten disease. So we decided to enroll Taylor in a little school for children with learning differences. It was a caveat. We would also provide a teacher for the visually impaired and as time went on a one on one. It was an expense that we never planned. But Jim and I would just look at each other and say, we'll figure it out later. I'm glad because it was one of the best decisions we ever made. Isolation can be almost as bad as the disease itself for these children. And this little school made sure that she was included and that she was cared for. On the first day of fifth grade, we arrived at the school and headed to Taylor's locker. The teachers had identified Taylor's space with this figure that you see on the left side of the screen. They knew my child well, Batten fighter. She was a fighter and they felt for her. The students not only included her, they embraced her and her time at the school was probably some of the best days of her life. Next, slide, please. Supporting Taylor's quality of life was job 1 for us and a full-time effort. Her weekly activities included 5 therapy sessions such as PT, OT, speech, aquatic therapy and orientation and mobility. We spent a lot of time in the car going from session to session. Her vision steadily declined, but her resilience was amazing. She adjusted to changes in her vision continuing to do the thing she loved. She could run up and down stairs and operate her boom box and the TV control like a champ. I can still see Taylor working on her custom-made Valentine's and writing her name on rail. There were other effects of Batten that weren't so easy to modify and control and they started to pile up around age 14 to 15. The movement disorder was probably the most impactful at that time on her quality of life. These movements usually began following moments of pleasure such as hearing the beat in the background music at her favorite pizza place or hearing children laughing and talking across the aisle at Target. Taylor would smile and she chuck a little. And as she connected with these moments and then the episodes would began, we learned to exit public prices quickly. CLN1 disease goes after everything, it can steal from these children, even these simple moments of happiness, our greatest fear was when these episodes became more prolonged because some of them did evolve into full-blown tonic-clonic seizures. We could rarely rescue them at home and it would result in a trip to the ER and sometimes a week or more in the hospital. At 15, Taylor was losing weight and swallowing was becoming more difficult. Her speech therapists suggested a swallow study. And I still remember the beautiful June morning as we walked into the hospital for the study. She was chattering away in her haltering manner -- halting matter, but she was chattering just the same. Study results showed that she was aspirating everything she swallowed. So a G-tube was scheduled within a few days. A week later, I heard my daughter say her last words. Mom, I'm hungry, and she never spoke again. Taylor's loss of speech had a devastating effect on her and her family. She could no longer sing along with the song she loved or tell us how she was feeling or what she needed, simple things such as our traditional Tuesday night dinners, when we all gathered for fun and togetherness changed. Our little extrovert could no longer express herself or be a part of the conversation and the pain was really deep. Families who've lived with CLN1 disease would probably tell you the first day of wheelchair the day that first wheelchair is delivered is a sad milestone. Our sweet girl, who ran 5 Ks with her friends and was going to school dances. Just a few years earlier, was wheelchair bound in her late teen years. In Taylor's final years, we had 76 hours per week of in-home health support, and it was a blessing because caring for these children can be demanding and stressful. Even during the night when we had care so that Gemini could sleep, I slept with one eye on the monitor beside my bad. I knew every time our home health care support checked on her or repositioned. Repositioning is important to avoid contractures and pain. We followed a strict schedule of stretches to avoid this pain, and there was a great deal of equipment to support the efforts. Taylor's room was filled with a stand, mats, balls, bolsters. We had an electric ceiling lift for transfers. Taylor slept in a large sleep safe bed for her safety and for ease of care. We fought long and hard for that bed and only won the battle when she managed to hurt herself by tossing herself out of the King size bed in her room. We'd added bed rails and the rails became our evidence of need. One of the rails was bent beyond repair, which she fell herself over it. We had to fight harder, believe it or not, for her shower chair. A CNA dropped Taylor while bating her and that again is easy to understand because she -- when you're trying to hold up a soap -- soap slippery girl and bathe her. I took photos of the results of that fall, the bumps and bruises to convince our insurance provider that Taylor really did need that shower chair. These experiences are just a glimpse into the life of those living with CLN1 disease. There is so much more that I could share with you. This disease will and can steal everything from a child. Family space, unimaginable grief and depression, isolation, financial hardship. I've had some families tell me that they actually feel guilt that they can't do more to help their child. It's a difficult road, and I'll be forever grateful for the support of our family and friends. They loved Taylor well. Next slide, please. I met Dr. Steven Gray, a scientist in the Gene Therapy Center at the University of North Carolina at Chapel Hill in November of 2011. It was another life-changing day in my life. Steve was working on a rare disease called GAN. His commitment to the science, his vision for expanding learning from the GAN study and his compassion for children and families living with rare diagnosis drew me in. And Taylor's tale helped to initiate a study that today live on in TSHA-118 for CLN1 disease. In closing, I hope that you're wondering how you would face CLN1 disease, if it happened to your child or your grandchild and how you would keep going under such physical and emotional burden. Gwen, next slide, please. When Taylor was diagnosed, my husband and I were told that we would not likely see a viable treatment targeting the underlying cause of CLN1 disease in Taylor's lifetime and possibly not our own. But sometimes, you just have to believe that things can be better and do what you can. Jim, Taylor and I found this quote on a footpath while walking the [ Greenway ] in our hometown of Charlotte, North Carolina. I'm sure you understand why it resonated so deeply for us then and even more now. It is hope that keeps these families going and can serve as an accelerator for progress. But hope is an action word. You have to do things for things to actually get better. Next slide, please. Thank you, Taysha. Thank you for your dedication, your commitment and for doing something to make progress and create hope for families like my own.

Thank you, Sharon, for sharing your story. It's wonderful to hear the patient voice and the caregiver voice. And we, in our audience really appreciate you sharing your story.

Thank you.

Yes. Thank you. Now, I'd like to introduce Dr. Steven Gray, Associate Professor in the Department of Pediatrics at UT Southwestern and Chief Scientific Adviser of Taysha. He will now be talking about the preclinical data for TSHA-118. Steven?

Thank you very much. And first of all, I just want to say to Sharon, thank you so much because you and Taylor are the reason why all of this happened. You reached out to me, this is the reason why we started on this, and this was the inspiration that kept our lab going to develop all the work that I'll present to you right now. So if you go to the next slide. So the approach, as I think everybody would be aware of, to try to treat CLN1 disease is a simple gene transfer of the CLN1 gene. In this case, we are delivering a human CLN1 gene that was codon-optimized, driven by a relatively strong ubiquitous promoter-based beta-actin promoter. And this was packaged in a self-complementary genome design, with -- and packaged with an AAV9 capsid. So if we go to the next slide, you can see this is not meant to go into detail on all of this, but really just to impress upon you the wealth of data and the breadth of the experiments that we conducted to develop this treatment and to understand how treatment with AAV9 CLN1 could benefit understanding the doses that would be effective that could translate to humans, understanding the ages that we might intervene and the points in the disease course where this might show a benefit and then ultimately, the safety of the approach that we looked at extensively in mice, in my own lab and also through a contracted toxicology study in rats. So if you go to the next slide, I'll just walk through the highlights of the results of all these experiments I think the most important thing that we can look at in the mouse model is survival. And we were using a knockout model of CLN1. These mice are published, they're well characterized. And they have -- they basically have a phenotype where, in our hands, the first point that we could measure and quantify any behavioral deficits was around 4 to 5 months old. But then the mice end up progressing pretty well. with minor deficits until about 7 months old, where they've been rapidly decline with a median survival around 8 months old. We tested initially intrathecal injections of TSHA-118. And you can see here kind of this age response at a high dose level where if we treat mice at 4 weeks old before symptoms, these over symptoms emerged, then we could extend the survival out to a median 18-month survival with some mice have any normal life span. And with -- and I'll stay with all of the data that I'm presenting that we terminated all the mice in a predefined schedule by 21 to 24 months old. Some other survivals would go out past 24 million. If we treat the mice later, at 12 weeks old, then we still have a significant and quite meaningful extension and survival that's a little bit less than if we treat them earlier. This is kind of a highlight of the data, but I'll go into some more detail on the next slide. And if you can bear with me, this is a very busy slide because we did very extensive experiments to try to understand what this treatment would look like and how we should plan it out as we're moving forward to translate to humans. And I'll focus on the panel on the left first. And the nomenclature here IT is for intrathecal LM and H is low, medium or high dose and those are defined at the bottom of the slide. And so you can see here that if we treat mice at 1 week old, and I would correlate this possibly to a human infant with classic CLN1 disease. Then we normalize the survival. We've got the mice with a median survival going out very similar to wild-type mice. If we drop the dose actually tenfold lower and we treat them at 1 week old, and this is the dash blue line, you still see a profound extension of survival. And then if we move this out to 4 weeks old, which is still very early in the disease course, then you can start seeing a clear dose response emerging where a low dose provides some benefit a medium dose is longer. And then the high dose, again, is bringing this out close to that of an unaffected mouse. And we did test this combination treatment, and this question came up, I think, from Joon Lee and Angela Schulz presentation of treating the systemic disease. And in this case, we tested this where we did a high intrathecal dose and then we tried to further dose escalate by giving an intravenous administration of the same vector at the same time. And so you can see when we treat the mice early, that combination of intrathecal with IV really doesn't provide any additional benefit. And as I'll show you later, one explanation for this might be when you do an intrathecal injection then a significant amount of the vector does escape and get into circulation. And so we still get high transduction of the liver and other peripheral organs leading to very high levels of PPT1 enzyme that circulates in serum for the life of [indiscernible]. So if we shift to the right panel. This is where we're treating mice really after the onset of overt symptoms that we can quantify. And so you can see here a clear age response where treating mice at 12 weeks sold with a high dose, gives us significant benefit in survival. But then if we move to 20 weeks old, we did a lot of experiments to 20 weeks old. Then there's this really graded response. There's a clear dose response. And so you can see this with the dashed blue line at the low dose, where treating mice early, the low dose was still quite effective, but treating mice that are symptomatic or after the start of over symptoms that low dose provided a minimal benefit. But then the high dose at that point when the mice are symptomatic does still provide a significant benefit. And then we explored again, this question of doing this combination treatment at this 20-week age where the mice are clearly symptomatic. And and this is where the data diverged a little bit from when we treated mice very early, pre-symptomatically at this later point in the disease, the combination of intrathecal or high intrathecal dose with a high intravenous dose, which is in the orange line going out there, it did provide a significant benefit over just doing the intrathecal alone. And then interestingly enough, if you want to look at this data carefully, you can look at the dark blue solid line and the light blue solid line of -- doing an intrathecal injection and an intravenous injection, these are both at the same dose per mouse that it actually provided a similar treatment benefit at this age. But we are going in with the intrathecal route of administration because this does -- when you start to scale to larger patients, especially then this would end up with a lower overall dose and it also avoids circulating anti-AAV9 antibodies that might be present in some patients. And then the last thing that I'll point out here with these survival curves is the green lines, solid and dashed. And this is where we're pushing this out, treating mice at 6 months old, where the symptoms are starting to progress more and we're starting to see some mice, the very first mice die shortly there after this time point that at this age, when the disease is more progressed, then you see that the benefit is quite diminished. So overall, the picture here is that early intervention for this disease is very, very important. But there is still some room for some benefit in patients that have symptoms, I think, if we're trading this earlier in the disease state. And the dose response is important, particularly at the older time points, whereas even if we treat very, very young with the low dose, the results can be quite profound. So if we advance the next slide, this is all looking at survival, which is kind of a crude, but very important, obviously, outcome. But we wanted to see how well the mice retained function speak to maybe a quality of life issues. And again, these -- this slide is very noisy. There's a lot going on here, but it's to show you kind of the breadth of the data. And the important take-homes here are on the left panel, if we treat mice before they have any over symptoms then we see basically the treated mice retain normal motor function basically for their entire lives. There is some slight deviation when you get to the older ages, but the mice are still able to perform this task reasonably well. And the ones that drop off are the ones where we treated a little bit later with the low dose, and we see this same sort of dose and age response as we saw with survival curves. If we treat mice after the onset of overt symptoms, then sort of the same story it gets played out that we saw with the survival curves where these mice at the time that they were treated we're not able to do this task really well and then they had a rapid the climate on this, just like we felt the survival curves. But the mice as they -- the ones -- the cohorts where the mice did live longer, they actually retained that motor function basically until they started to to die. So if we go to the next slide. This is just looking at other assessments. So basically, all of the behavioral testing that we did and when we put these mice through a battery of various behavioral tests, they all showed essentially the same thing. So if we looked at grip strength that was measured by hanging time. So this is where you put the mouse on a wire grid, you kind of shake it so they grab on to it and then you turn it upside down, and it just measures how long the mice can hang on to that wire grid hanging upside down. And so if we treat the mice before the onset of symptoms, then they retain the strength basically throughout their lives. And if we treat them after the onset of overt symptoms, and you start to see as the mice meet their end of their lifespan, they lose this function, but the mice that live longer preserve that strength. So if we go to the next slide. This is -- we were testing the mice in the more water maze but what this test ended up being. And this is where you put the mouse in a pool that's filled with opaque water and you're measuring how long it takes the mice to find a platform that's partially submerged under the water. In this case, the data that was very informative from this test was actually video tracking of the mice where you could calculate your swim velocity. And so this is a very stringent test. And I think I'll start off with the right panel this time when we treat mice whose symptoms after the onset of overt symptoms, basically, the untreated mice past 6 months cannot do this task. They can't float. They can't swim at all. And so when we treated the mice very late, we really -- this was a very physically demanding task for them to swim. And we were actually quite encouraged that we -- when we treated the mice at 28 weeks old with the combination of intrathecal and IV, then the mice could actually preserve enough function to continue to swim on this task. But then if we go to the left-hand panel, you can see that the mice continue to be able to form this task quite well. And for kind of logistical reasons, we ended up having to basically stop this test after 12 months old. So if we go to the next slide, I wanted to shift away from the behavioral testing and talk about enzyme activity so we could measure the PPT1 enzyme in these mice. And one of the things that we did, well, it was difficult to measure in the CSF just because of the very, very small CSF volumes in mice and the difficulty -- technical difficulty collecting it, but we could look in serum and when we can look in tissue. And in this case, when we looked in the serum of the blood of these mice, we always saw the supraphysiological levels of PPT1 enzyme. This is a log scale, so we're talking about, in some cases, 100 or 1,000 times normal levels of enzyme that are circulating in the blood basically -- and we saw this extended for the life of the animals. We did follow mice out to 18 months to look very carefully at any safety concerns. And also in rats after 6 months old post injection, and there were no adverse consequences of overexpressing this enzyme to this extent for the life of the animals. But you can imagine if we were thinking about something like an enzyme replacement therapy, you would never -- having this level of sustained enzyme, this would be quite -- be viewed as quite an effective enzyme replacement therapy, except that the enzyme in the blood doesn't get to the brain. So that's where we're really acquiring this gene therapy approach to specifically target the central nervous system. So if we go to the next slide, I can kind of wrap this up, and one thing that I didn't really highlight is the safety study that was done in normal rats. This is a GLP safety study and rats were dosed at 6 weeks old by intrathecal administration, some were given IV administration. And those rats were followed out the longest time point with 6 months post injection. And this ended up being, frankly, a very boring study because there were -- there was no evidence of adverse findings in this study, up to doses exceeding what would be proposed in a clinical trial. I also want to highlight from the mouse study that we found a -- especially in presymptomatic animals that there was a wide dose response, where the lower doses could still provide a significant and meaningful benefit. But when we push to the high dose, that ended up being required more so for the later treatment ages. And we definitely showed evidence of widespread distribution, widespread expression of the gene across the brain, spinal cord, other organs. And so overall, this is a, I'd say, a successful study, and we're very excited to have Taysha pick this up and move it forward to patients like Taylor that desperately need this. So I'll wrap up there, and I'm happy to take any questions.

Great. Thank you, Dr. Gray, for your presentation. Our first question actually comes from Raju Prasad of William Blair and his question is for Dr. Schulz and Dr. Gray. Can you discuss the importance of targeting the soluble enzyme-based CLN diseases with gene therapy? Does that derisk an AAV-based approach at all in your view?

Sorry. Was that directed to Dr. Schulz?

Yes.

Okay. I thought it would be to both of us. Well, I think such -- I mean we do have the great condition that there is a soluble enzyme, and we were able to detect and measure enzyme activity now also with new methods like mass spectrometry, where we're really able to also look at very robust numbers of enzyme activity. So I think this is an important part with regards to looking at outcome measures. However, given the idea that probably enzyme is going to be used by the neurons and also heavily used probably the amount of enzyme that you might be able to detect in the CSF will probably not really reflect what is already positively impacting the neurons. So usually, and probably, Steven, you have to correct me if I'm wrong, but my understanding was that usually neurons would release the enzyme if they do have a lot enzyme, but otherwise, they might really use it up. So probably whatever we detect in the CSF will be even lower, and we would have to extrapolate that there will be more within the neurons, at least that would be my understanding, not being a neuropathologist.

Yes. Maybe -- maybe I'll follow up to say whenever -- with AAV9, the pattern of transduction, we would target neurons, we would target astrocytes, we'd target other glia, target ependymal cells. And so some of these cells would use the enzyme things like the ependymal cells will be secreting this into the CSF, most likely. So I think it's hard to say exactly to what Dr. Schulz was referring to, but because you could have local spread of the enzyme, say, from astrocytes or oligodendrocytes to neurons that wouldn't -- that might not even show up in the CSF. But then you're also if you're producing the enzyme that's circulating the CSF, then it's able to spread throughout the brain beyond what the spread of the virus might have achieved and essentially do an enzyme replacement therapy approach with that circulating level of enzymes. So it would be like is reminiscent of the Brineura for CLN2, but on an ongoing basis, where the brain is -- or the cells in the brain or the factories to provide the enzyme on an ongoing basis without repeated injections.

Great. Thank you very much for addressing that. Your next question comes from Joon Lee of Truist. What's the rule of thumb when you scale up intrathecal dosing from mice to human? Also, you showed data using IT and IV dosing in mice. Have you tried intraparenchymal dosing?

Well, maybe I'll address the first -- in terms of intraparenchymal dosing, these are approaches that have made it into the clinic for multiple gene therapy trials. But in terms of trying to get widespread distribution of the vector to all areas of the brain and the spinal cord. I'm not aware of any studies that have really been able to achieve that with intraparenchymal injections. The number of injections you would have to do to get adequate spread throughout the brain and it would be staggering and not feasible. So there are other labs that have looked at that. Mark Sands' lab, Washington University has tested intraparenchymal injections in young mice. But those studies look very positive because you can fill much of the mouse brain volume with the injections. But when you scale it to humans, you just -- you can't get that degree of spread. So in terms of translating to humans, there's multiple approaches to try to calculate this. It can be by CSF volume. It can be by brain mass, it could be by body weight. But I think body weight is probably a bit inaccurate because patients can be different sizes. But if you scale essentially by CNS mass or CNS volume, then -- that's the metric that we've used across any gene -- CNS-directed gene therapy approach, and I think that's become standard for the field.

Great. Thank you. Your next question is a from Joon Lee of Truist. In peripheral tissue and cells, do you see lysosomal inclusions, such as the granular inclusions that you see in neurons?

You just cut out just a little bit there. Can you repeat that?

Yes. In peripheral tissues and cells, do you see lysosomal inclusion such as the granular inclusions that you see in neurons?

So to be -- Angela, would you be able to address that, the peripheral -- the organ pathology?

Well, we do see the lysosomal inclusions in almost all tissues of the body. But for some reason, I think the neuronal cells seem to be most really affected by the disease. In addition, looking at lysosomal inclusions and the extent of lysosomal start probably might not necessarily correlate with really outcome because we know from other studies that you might be able to get rid of lysosomal storage material, but still do not have the ability to change the phenotype. So in contrast to what we thought years ago that the lysosomal storage material really is the toxic part to the cell. And if we're able to can rid of this lysosomal storage material, the outcome would be improved, I'm kind of doubtful to that. So detecting or not detecting the [ storage ] might not be the best outcome measure at least to what I know from other clinical trials.

Yes. And maybe I'll follow on that to say this is one reason with all of our studies that we focus primarily on functional outcomes in the animal model. We focused on survival benefits. We focused on improved motor function improved strength improved cognition because ultimately, if you're fixing these underlying biochemical or pathophysiological problems, then there's a good reflect in improved function of the mice and improved survival of the mice.

Great. Thank you. Your next question comes from Laura Chico of Wedbush. Dr. Gray, I believe all the animals has supraphysiologic PPT1 activity in plasma following administration of TSHA-118. Could you add some context around what percentage of normal expression you would anticipate in humans at 5E to the 14th VG dose?

Yes. I'm sorry. It's really difficult for me to extrapolate that. I could say that I would certainly expect in the serum that we would get supraphysiological levels from the mice. As I said, there were just -- there's technical limitations in terms of being able to collect the CSF from mice and being able to collect enough CSF to assay PPT1 activity. So I'm sorry, we just don't have the data for you to answer that.

Suyash, would you like to comment on that as well?

Sure. I think that I think Steve is correct in that we're going to see supraphysiological level of enzyme in the serum. And it's true it's hard to extrapolate from the mouse studies because as Steve has mentioned is you can't take CSF -- in the small amount CSF available in the mouses, microliters and you can't take it and sample it. What I would say is that the 5E14 total we dosed -- VG dose is a pretty high dose when we look at some of the other intrathecal dose gene therapies out there. And the one that we like to spend some time on is our giant axonal neuropathy program, where we're seeing really nice clinical stabilization of disease of the 3.5E14 dose. So 5E14 is a pretty high dose. While I'll also say is that this is a secreted enzyme. So even though you may be get transduction of a certain proportion of the cells within the brain, the enzyme is such that it leaves each cell -- it gets extra-cellular traffic after it's broken down the palmitoylated substrate within the lysosome in [indiscernible] [ that we've been talking about seen from electron microscopy ] [indiscernible] that particular cell, this extra cellular traffic can enter another cell through the mannose-6-phosphate receptor and break down additional substrate there. And that can once again leave that cell and enter another cell. So you only need a small [indiscernible] -- because it secretes, it's actually affect a really significant pathological difference, which will hopefully translate into a clinical [ standardization ], [ if not in clinical improvements ].

Great. Thank you very much. Your next question -- Suyash, your next question comes from Kristen Kluska of Cantor Fitzgerald. As this preclinical data further validates that earlier intervention is correlated with greater outcomes, how will the company work with third parties and organizations to ensure patients are being diagnosed earlier?

Sure. Thanks for the question, Kristen. And yes, in terms of patient finding activity, we always have a similar approach across all of our rare diseases, which are -- we engage with and interact with key opinion leaders who treat us [indiscernible], we work with professional organizations, so they are the first hear about the patient in some parts of the world. And we have a field team with on the ground based on the ground activity going out there and finding patients. But you're absolutely right, Kristen, the key thing here is that as you've heard from Steve, from Angela that we actually need to -- you actually need to treat earlier before the chance for neuronal loss has had a chance to take hold. And I think -- we're working with groups like Invitae and GeneDX. These are programs that, as once again Angela mentioned, the [indiscernible] organizations for particular diseases was with looking at the actual cell side under the [indiscernible] now in the mutation analysis. And now there is big panels where a chart presents with a few seat symptoms and the position in media sets off a blood spot or blood sample for a whole test of 20 - 25 of these diseases. So the diagnostic age is reducing further and further. In addition to that, we're working very closely our Head of Government Affairs, Emily McGinnis, who has real expertise in newborn screening and how to get newborn screening moving forward. She was able to do that with the SMA program. So that's now being implemented in many, many states around the world, as to diagnose patients earlier, either in the very early stages of symptoms or even pre-symptomatically. So working very hard to -- working very hard to try to get newborn screening panels to include the CLN1 assay, which is -- the technology is absolutely [indiscernible] and now it's more a policy and political decision to move that technology of the newborn screening. So those are things we're doing to try and make sure the diagnosis is made earlier and earlier. But as you can see, the data has cleared that the earlier you treat the better, which is the case also for many of the other [indiscernible] disorders.

Great. Thank you, Suyash. And I just wanted to go back to addressing Laura Chiko's question from Wedbush that just to clarify that we haven't seen the 3.5E to the 14 dose yet or 1.8E to the 14.

Absolutely, Kim. Thank you for correction. Just to clarify, yes. Patients in the GAN study being dosed to 3.5E14, we've only seen the 1.8E14 total VG data. Thanks for clarifying, Kim.

Yes. No worries. Thank you. Great. And your next question comes from Yun Zhong of BTIG. Did you evaluate memory with more Morris water maze testing time to find the floating platform?

Yes. That ended up being technically tricky because the mice -- one of the phenotypes it was a visioned very early and the Morris water maze is dependent on those unrecognizing visual cues around the tank. So that just ended up being a confounding variable that made the data difficult to interpret.

Okay. Thank you. Your next question comes from Silvan Tuerkcan of JMP Securities, great presentation. Could you please comment on the discrepancy between supraphysiological levels of active PPT1 levels, and yet survival is not completely rescued?

So there's data that has been published out of John Cooper's lab at Washington University in St. Louis that where they've looked at the pathology of these mice, and it starts very, very early. I think that they can detect pathology in these mice as early as 1 month old by histological methods. And so when we talk about symptomatic and presymptomatic there's inflammation and there's degeneration that is occurring very early in these animals that may, in some cases, be predating the symptoms that we can assess and quantify by our measures in the mice. So I think that, that probably touches on a theme across all neurogenerative diseases that once the disease process is set once there's significant neurodegeneration that happens, you might be able to stop or slow that. But I think that it's an open question about whether there's any potential for reversibility. So I think that the efficacy at the different treatment ages even when you have these high levels of enzyme activity is just a reflection of what is lost, what is left to preserve. And I should also say that when you talk about supraphysiological levels of enzyme circulating in the blood, we don't -- there may be lower levels that are in the central nervous system. We may be getting those high levels, say, from overexpression in the liver, for example. And it's understood that the enzyme does not cross the blood-brain barrier going from the blood into the brain.

Great. Thank you. Your next question comes from Yun Zhong of BTIG. This is directed to Dr. Schulz. If patients are automatically genotyped for CLN1 when tested for CLN2, with the approval of Brineura, have you seen more CLN1 patients diagnosed?

Yes. This is indeed the case. We have more patients being diagnosed and also we do see the patients being diagnosed much earlier now. And I think this is an important improvement with regard to any upcoming clinical trial because the earlier we can start children on treatment the better.

All right. Thank you very much for that. And thank you, Dr. Gray for your presentation and for you and Dr. Schulz and Dr. Prasad's Insights. We'll now end this Q&A session, and I'd like to now introduce Dr. Prasad, who will be speaking on the clinical development strategy for TSHA-118.

Great. Well, thank you very much, Kim. And yes, we've heard from Angela and Sharon and Steve -- Angela gave a very nice overview of the disease and her thoughts as to what's needed as we move forward into clinical development for CLN1 and learned some other lessons towards the such cells. So Sharon gave us a very eloquent description of the burden of this disease and how it's affected her and her family, which was really very moving and very impactful. And then Steve, of course, outlined his very comprehensive preclinical package of data, which has been the essentially -- forms a part of our discussions with regulators over the past few months. I'm not going to take those pieces of information and weave them into our clinical development strategy and talk through our thinking and plans in that regard and what we have been doing at Taysha specifically. So next slide, please. So we had a busy year on CLN1. We've run a couple of advisory boards. The first one was in March earlier this year, where we brought together a number of the world's experts calling Batten's disease, including Angela and Steve and others. There are a few specific learnings from that. Now, I'll take you through some of those earnings in a moment. We've also run a number of CLN1 patients focus groups in the early part of the year. Now this is very, very important. We've seen how the patient story, the patient narratives weaves into everything we do at Taysha across all range of programs. And in addition to hearing from wonderful speakers such as Sharon, we also spend a lot of time in a very formal way exploring what it is specifically the effects patients and families and children themselves and use those insights and weave them into our clinical development strategy and our regulatory thinking. And we're going to give you some specific examples of what we learned from those and how it impacted clinical trial planning. We've had a number of interactions with regulatory agencies on our CLN1 program. In fact, across our portfolio of programs. And those have been really very positive, and I can touch on that in a moment also. We've completed our GMP (sic) [ cGMP ] drug product fill. So we have a significant amount of high-quality product ready to be used in the clinical trial. There's a little bit of release testing yet to be done, but we're very confident this will be suitable drug for the clinical trial. We'd like to publish the work we're doing. So we're presenting the study design and thinking around outcomes, assessments and also the patient feedback work we've done with the International Congress of NCL diseases, which is taking place in St. Louis, I believe, in October this year. And interventional protocol, essentially, is near complete, we just have a few minor matters to complete before they can be the interventional protocols [ can be signed on ]. Next slide, please. So as I said, we had a nice scientific advisory board; a very in-depth discussion. Two of these early on in the year, including Batten's experts, gene therapy experts, CNS disease experts, and metabolic medicine, experts from around the world. And they gave us a lot of nice insights on clinical study design and thinking and how do you identify patients, what should we have as inclusion/exclusion criteria. If the next slide, I'll take you some of the specific learnings. And this is an important slide, please. And next slide, please. So in line with some of the companies already diagnosed, as typically confirmed with genetic testing now. And a few years ago, it wasn't done that way, it was done histopathologically, now it's done by genetic testing. Sometimes early, specific clinical diagnosis may be challenging due to common nonspecific initial symptoms, which you heard when you heard Sharon's story. But nowadays with panels such as run by GeneDX in detail. As Sharon presents with some nonspecific features, types of developmental delay, perhaps some visual loss and then a tested for a whole host of metabolic and neurological diseases at [indiscernible]. So the diagnostics rates are improving and also diagnosis is apparent key at younger age. We've spent a lot of time talking about PPT1 activity. I'll have a slide later on in my deck, that goes into a little more detail also. And we've also talked about how hard it is to give specific numbers on what would be appropriate and meaningful in terms of paralleling it would like expectancy and [indiscernible]. Having said that, the general thought amongst the key opinion leaders, we got together was look, if you improve the PPT1 activity from 0.1% to 5% that will be positive, especially given the fact that adults may range between 4%, 5%, 6%, 7% and 8% from what we know at the current model. So from our perspective, anything over 5%, maybe over 10% would be seen as a real positive. And as we've already heard, it's likely that we don't need a great deal of enzyme to make a dramatic change in clinical circumstance -- it's a secreted enzyme, so a little of this enzyme goes a long way. The third point was -- talking about different outcome measures and about how they may need be slight different from phenotype to phenotype. So often a slow attainment of skills is -- or by regression, and the incidence of vision loss is actually common across the three pediatric groups of patients. And seizures and behavioral issues may also occur, prior to visual deterioration in some [ juvenile ] patients also. So we've given some thoughts specifically as to what end points might be more appropriate for which specific clinical grouping of patients, [indiscernible] one of those. Talking about the [indiscernible] of study. Now another point, which I think is important, and we've touched on some of the questions is the fact that there seems to be some accumulation, or inclusion of pathological substrate, extra CNS outside the central nervous system. But it doesn't seem to have a great deal of clinical impact apart from perhaps a slight amount of cardiac compromising the juvenile population, as Angela mentioned earlier. What I will say about IT administration, I think it's the important thing is not to forget the IT administration, actually, you can think about it almost as a dual IV IT route administration because between 40% and 50% of the drug is given intrathecally, will actually leak out in the systemic, so where it can actually then transduce to the liver, transduce other organs and therefore, increase levels of PPT1 extra CNS. And if there are indeed any extra CNS manifestations of the disease, we do cover that to some degree with intrathecal dosing of drug. The other point that I think is important to reemphasizes the fact that when an infantile patient starts to experience signs and symptoms, some degree of neuronal loss is already occurring. And based on Steve's preclinical data and our general thinking about lysosomal storage disorders in general, lower-doses, early-treated patients, many more effective [indiscernible] often than giving a high dose to a late treated patient. And what we mean here is that the earlier you treat a patient and more likely the better outcomes. So actually, early treatment rather than late is more important, than the actual is needed to be given. We've also spent a lot of time thinking about the outcome measures that are specific to the patient. And that produce a clinically meaningful change for patients and families. And this is important, and you'll hear how we've done this specifically when I'll talk to our patient focus groups. But this is really important from the perspective of the FDA, EMA and these all regulatory agencies. There's an increasing focus on listening to patients and families and what are clinical outcomes meaningful for patient and family rather than what the doctor feels is necessarily, clinically meaningful. And you can see this with increasing workshops with the FDA running and the greater focus on these patient reported outcome measures. In general, what I will say is the key opinion, we're very enthusiastic about our program, very optimistic about the gene therapy program. They are very compared by the preclinical data and as you can see, there's a real clinical urgent medium this particular population of patients. Next slide please. Okay. So let's talk about the patient focus group. So we do this really for two big picture reasons. One is we're really curious we want to learn about the patient experience on some of the most challenging symptoms, quality of life impacts develop endpoints appropriately and uncover any education gap we need to be [indiscernible] and also, we want to collaborate with the patient community, the patient community are incredibly important for us to be able to run a successful clinical development program and indeed have successful regulatory interactions. Next slide, please. And some of our approach is in a very disciplined way to develop a very formal questionnaire, do a pre-screening questionnaire before the meeting. And then remotely, we're now doing this remotely in the times of COVID, we're actually spending time going through the [ system ] questions, really soliciting in-depth feedback with an external facilitator in a disciplined way. So for this particular group for this particular program, we spoke to 12 CLN1 disease caregivers across the breadth of infantile, late infantile and juvenile CLN1 disease. We did this in fact in a number of -- Batten's disease and CLN1 organizations. And with the next slide, I'll show you some of the feedback. And it theres a lot of what you heard from Sharon earlier on today about what's most meaningful to the -- what was most meaningful to her and Taylor as Taylor progressed with CLN1. So communication is a big, big issue, of course. The ability to speak -- the ability to speak deteriorate at times, especially when it's coupled with vision loss. It really impairs the ability of the child to communicate with the family. So spending time looking at both communication and vision, is important. You'll see how we've done that specifically in our clinical design. You can see inability to sit, stand, walk and other major gross motor milestones. These are really important also. And so we've built that into clinical trial program, the ability to -- some of gross motor milestones, the ability of a child to sit , the ability to stand better, to also walk by themselves. [indiscernible] we've spend time, we're thinking about that. Seizures is a big part. We're looking at seizure activity in the clinical trials as well as in general, cognitive scales to look at any kind of decline in mental development over time and maybe stabilization and maybe even improvement in developmental progression in the children. Next slide, please. This slide calls out some of the specific quotes we heard from some of the patients and families. I won't read through these now. Many of these quotes actually do reflect some of the sentiment you heard from Sharon earlier. I'll let you read this in your own time. But you can see once again, cognition, mood communication speech is a big issue, seizures are big issue, motor decline is a big issue and vision is a big issue. But I can only reemphasize the significant burden of disease that these children and families undergo. Next slide, please. So this is the clinical trial, and I'm going to touch a little bit on the clinical trial and then when I talk about endpoints you'll see how we weaved the patient feedback and the KOL feedback into that. In terms of critical endpoints, biomarker activities, specifically PPT1 activity and the CSF is going to be our key biomarker endpoint. Of course, there are other biomarkers we can look at, for example, the accumulation of substrate, palmitoylated and how that reduces over time, that will be looked as well. But I think the most important biomarker we need to look at is PPT1 enzyme activity. From an efficacy endpoint perspective, looking the whole breadth of pathologic physiologic function and clinical markers, and I'll touch on that in a couple of seconds time. The intent will be to have 2 dose cohorts, 5E14 total VG, being given intrathecally and 1E15 total VG being given intrathecally. Once again, we get the drug intrathecally, you can see the bottom right hand corner of this slide, we pop a needle into the this slide. We put a needle into the L3 and L4 or the L4-L5 space for the child turned on to their side. We drain out a few mills of CSF. We then attach the tubing, attach the syringe, which we then and slowly inject by hand on the syringe drug to inject the drug. Approximately 10 mills over approximately 5 to 10 minutes. We then take the needle out and then put the child on the back and then tilt their head down in the Trendelenburg position for about an hour. This does 2 things. It helps pull CSF around the brain and it also helps a post-lumbar puncture headache, which is one of the known immediate consequences of a lumbar puncture, a headache, which you put the child on their back and head down which actually seems to relieve the [indiscernible]. So that's the clinical trial design from an outline perspective. Let's go to the next slide, please. And I want to focus a little bit more touch on this a little bit more. We've talked about PPT1 activity and talked about the relationship with neuronal loss. But I wanted just to folks to listen once again, which is a really important point. So the disease pathology is due to a loss of function mutation with PPT1 gene. This encodes the enzyme PPT1, palmitoyl-protein thioesterase. What this does, it's a soluble enzyme can move from cell to cell, it breaks down this palmitoylated substrate. And in the absence of the sense we can build up of these inclusions within the lysosome, the lysosome swallow the inclusions they then rupture, they can rupture and leak out their acidic enzyme lipid contents and cause neuronal loss. And you can see the graph on the right-hand side, you actually can get early disease even asymptomatically you're getting this accumulation of palmitoylated substrate early on and neuronal loss starts to happen -- and it's only once the neuronal loss has started to some degree that children actually will start to present. So some degree of neuronal loss has occurred, some degree of damage that may not be reversible has occurred by the time it shall present. This is why it's important to diagnose earlier, with even screening and treat as early as possible. And the likelihood is in line with Steve's preclinical data with the earlier treatment, more likely are to get an optimal outcome. So replaced in the PPT1 gene, the [indiscernible] PPT1 gene -- we've talked in the group for these disease, which is the loss of the PPT1 and so on. Let's go to the next slide, please. Now in terms of efficacy endpoints, I've touched on PPT1 activity in the CSF. We will, of course, measure in serum as well, which I think will be important. The life with -- is that one will be high. And I think the CSF level of the enzyme is going to be more flatter than what's going on in the brain. It won't be an exact proxy, but will certainly be the most accurate proxy and what's happening in terms of PPT1 activity in the brain cells itself. There are 2 key disease-specific or Batten's disease specific endpoints that we'll include. And that has precedence over some of the other diseases such as CLN2, CLN3, CLN6. Unified Batten Disease Rating Scale and the Hamburg scale. And Angela has touched on both of these scales earlier on in her presentation. In general, the UBDRS seems to be more appropriate for the juvenile patients and in general, the Hamburg scale is more appropriate for the earlier patients in infantile and late infantile patients. We'll look at many of the same features. So seizures, motor activity, behavior, functional capability, et cetera. And there is precedent once again, as I mentioned, on the CLN2, CLN3 and CLN6. In addition to that, we'll be looking at the Bayley-III scale, which is a cognitive scale, which looks at on cognition, language and motor activity. I think the most important scale here is likely the motor scale, in terms of gross motor milestones and how -- for example, child could sit by themselves, stack blocks, reach our by some object, have some object from coming to hand. So that's the important developmental progression scale to look at those specific milestones. And we will, of course, be looking at the Clinical Global Impression of Improvement scale, which once again is a more of a global measure, and it's a physician-rated way of assessing how well the child is doing. That has a lot of precedent. Now next slide, please. Those were the key efficacy points. The next slide now shows the secondary and exploratory endpoints. And you can see that bucketed into a few different buckets. So top right, you can see we've got other biomarker activities or [ accumulation ] palmitoylated substrate in particular. Communication is a key important outcome -- assessment to look at. As you've heard already, and it's a very nice scale, the ORCA, Observer Reported Communication Assessment, [indiscernible] by the receptor, and express their language capabilities and we'll be using that particular scale. Quality of life we'll be looking at. You heard about many of the issues with these children, that affect sleep, for example. There's other disease-specific assessments such as the CHOP INTEND, what was the seizure activity, frequency, duration, what are the medications, the child's own [ from ] seizure perspective. The Vineland-III for adoptive behaviors, cognition with the WPPSI-IV or WISC-V, depending on the age of the child. A lot of in-depth look -- look in the eye, so electroretinogram, [indiscernible] look at [indiscernible] layer thickness and visual acuity. So we'll hopefully see a stabilization in the ongoing progression of vision loss and hopefully an improvement over time. And then brain scans, Angela showed some nice images of a brain earlier and we'll look at the MRI to have volumetric changes as well as EEGs. Next slide, please. So I've talked a little bit about the KOL feedback from our advisory boards, I've talked a little bit about the feedback we've had from patients and families. And you can see those being presented -- that information being presented in abstract form at the NCL meeting in a couple of months' time, sometime during October. In terms of the next steps for TSHA-118, there's an ongoing collection of natural history data, which as you heard from Angela is being done up to regulatory standards and has -- [indiscernible] previously for an approval with Brineura, and CLN2. We'll be initiating Phase I/II clinical study in the second half of this year. We'll continue with patient finding activity with our key investigators and patient organizations and working with groups such an Invitae. And of course, site activation activities are ongoing in the U.S. outside the U.S. currently. So looking forward to starting the clinical trial towards the end of this year. On that note, I'll stop. Once again, thank my colleagues on the -- who spoke earlier, and I'm now also happy to take any questions.

Thank you, Suyash. We have time for just one question. The question comes from Eun Yang of Jefferies. Given the CNS mass and size increase as patients become older, do you think the initial target enzyme activity level should be greater than 5% to 8%?

I guess my feeling -- I think -- if a child is going from 0.1% to 5% to 8%, that's going to be a dramatic change. And given this is a secreted enzyme, we know that a little bit goes a long way. We know that from our expression of other enzyme with [ poster ] therapies. Do I think we'll get greater 5% to 8%? We may actually yet, quite a bit higher than 5% to 8%. And what I would say is the CNS mass and size is actually doesn't increase as much as other organs frankly. As any pediatrician will tell you that the organ that is the largest in comparison to the rest of the body is the brain at birth. That's the only -- increases the least in size over time, whereas other ones are, [indiscernible] from birth to old one. So I don't think -- I think a target of 5% to 8% is fine. We may well get higher than that. I don't think the increase in CNS mass or size really is that relevant. Hope that answer your question, Eun.

Great. Thank you, Suyash. And thank you, all our panelists for and speakers for your presentations today and for all your insights. I would love to now turn the call back over to RA Session for his closing remarks. RA?

Thanks, Kim. Next slide. We have enjoyed sharing in greater detail our TSHA-118 for CLN1 program with you. Looking ahead, we'll continue to focus on rapidly advancing our portfolio with many key milestones over the next 6 to 12 months. Lastly, I would be remiss to not thank but really appreciate Dr. Schulz, Dr. Gray and Sharon King with spending time and sharing their stories and insights with us this morning. Again, we appreciate you guys joining and the slides will be on our website for download. But more to come later this year with our Rett Syndrome Day in September, our Angelman Syndrome Day later in October. So thank you all for joining. Have a great day.