HDBuzz

Last month, we relayed positive news from uniQure’s trial testing AMT-130, a gene therapy delivered via brain surgery to lower huntingtin (HTT). Data released by uniQure in June suggested AMT-130 was safe and well tolerated in the small group of people that were treated with a low dose of the drug. Now we’re back to provide an update on findings from the group of people treated with a higher dose of AMT-130. This new set of data shows that the higher dose of the drug may be causing serious side effects. This doesn’t necessarily mean AMT-130 doesn’t work and won’t move forward, but it does mean that we need to take a pause, really look into what the data are telling us, and work out a safe plan to move forward for people being treated with the drug.

Despite setbacks, HTT lowering is still considered an attractive strategy by many researchers

One advantage researchers that study Huntington’s disease (HD) have is that we know exactly what causes HD – an expansion in the HTT gene. The expanded HTT gene produces an expanded HTT message that is then processed into an expanded form of the HTT protein that causes damage in brain cells. So, in theory, reducing the presence of that expanded HTT protein could alleviate the symptoms associated with HD because it directly targets the root cause of the disease. This means that despite recent setbacks for several clinical trials designed to lower HTT levels, HTT lowering is still considered an attractive strategy for HD therapeutics by many researchers.

There are several different ways researchers are trying to lower HTT. The first horse out of the gate in the HTT lowering race were antisense oligonucleotides (ASOs). These are short sequences that bind to a specific message which then cause it to be degraded. Without the message, no protein can be produced. So while the gene remains intact, the protein is never made. This type of HTT-lowering technology is being explored by Roche with their drug tominersen that took a step back to find the right dose and patient population. Wave Life Sciences is also using ASOs to selectively lower the expanded copy of HTT with their ongoing Phase I/II trial for WVE-003, SELECT-HD.

Another way to lower HTT that’s being tested in clinical trials is through “splice modulators”. These are drugs that change how the genetic message is edited. Like a story, every gene has a beginning, middle, and end. The end is a specific sequence that tells molecules in the cell to stop reading the code for that gene. Splice modulators work by editing the message to move that ending code up, confusing the sequence of that gene. So rather than a beginning, middle, and end, the story is just a beginning and end. The cell recognizes that this makes no sense and stops producing that protein.

HDBuzz recently wrote about the splice modulator branaplam, being tested by Novartis in the VIBRANT-HD study, for which dosing was suspended due to safety concerns. Another splice modulator, PTC-518, is being tested by PTC Therapeutics. Even though PTC-518 works in a similar way to branaplam, a head-to-head comparison of these drugs suggests they are actually quite different. So bad news for one doesn’t necessarily mean there will be bad news for the other. We’re still eagerly waiting for news about the PTC-518 trial!

AMT-130 is a one-shot gene therapy approach to lower HTT

A third way to lower HTT is through gene therapy, which is the technology being used by uniQure with AMT-130. This drug works by using a harmless virus to deliver DNA instructions that will destroy the HTT message. The HTT gene still exists in its original form, but now the cell contains a new message that will prevent the production of the HTT protein. Because the cells infected with the harmless virus contain the genetic instructions, they can make the HTT lowering message all on their own. This means AMT-130 is a one-and-done approach – deliver the therapy through a single procedure, and the cells will continue to make the instructions that allow them to lower HTT. This is both exciting and nerve-wracking. While it means only one treatment is necessary, it also means any changes are likely permanent.

To get AMT-130 directly where it’s needed most – the brain – it’s delivered using brain surgery. Because brain surgery is always risky, this trial was rolled out very slowly to be as careful as possible. After the first 2 surgeries were complete, the participants were watched to make sure there were no immediate negative effects. When everything went well, surgery for the rest of the study participants continued.

The trial testing AMT-130, HD-Gene-TRX1, is a Phase I/II designed to test safety and tolerability of the drug as well as find the right dose that will work for people with HD. Because one of the primary goals of this study was finding the right dose that will work best for people with HD, 2 groups were tested: a low dose group and a high dose group. Scientists at uniQure believe that the higher dose of the drug will not necessarily lower HTT further in each cell, but that more drug will mean that more brain cells will have their levels of HTT lowered by the same amount.

36 people in total were enrolled in uniQure’s AMT-130 study: 10 that received an imitation surgery that will act as the control group, a critical part of any study, and 26 people in the treatment group. Of the 26 in the treatment group, 12 were treated with a low dose of AMT-130 and 14 were in the group for the high dose. So far, 12 of those 14 have undergone surgery.

In June we got an update from uniQure about people that were treated with the low dose of AMT-130 12 months after their surgeries, which HDBuzz wrote about. In that group, the surgeries and drug were well tolerated with no major safety issues reported. uniQure shared that preliminary data indicating that HTT seemed to be lowered more in the group treated with AMT-130 than the control group. While this is exciting news because it means AMT-130 appears to be doing what we want it to do – lowering HTT – this was reported in a very small group of only 4 participants.

Some participants in the AMT-130 study have suffered serious side effects

In early August, uniQure made an announcement about participants from the high dose group in the AMT-130 study. Three participants (out of 14) from this arm of the study were found to have severe adverse reactions by an independent safety review committee. Two people that underwent surgery in Europe reported swelling and a third person, treated at a U.S. location, reported a severe headache and related symptoms shortly after surgery. While this is very upsetting and disappointing news, importantly, all three patients have either fully or substantially recovered and have now been released from the hospital.

What’s next for AMT-130?

There are many theories as to why these patients suffered these side effects, including some form of immune response. However, there is no clear or definitive explanations just yet and we must wait for further information before jumping to conclusions.

While the safety review committee doesn’t suspect the effects observed in the high-dose group of the trial are due to the drug itself, surgeries for the remaining 2 participants in this arm of the study have been halted for now. The low-dose arm is proceeding as planned and all trial particiants – in both the low- and high-dose groups – will continue to be followed for the duration of the trial. uniQure still expect to report data from the trial according to the originally planned schedule and we will be hearing further updates from the company about this trial in early 2023.

What does this mean for HTT lowering as an approach to treat HD?

The HD community has received disappointing news from many of the HTT lowering trials now and it is easy to feel like perhaps this is not a good strategy to keep pursuing to try and treat people with HD. It is important to keep a few things in mind though as all is not lost just yet. All of these trials have suffered very different problems and we only really have theories for why they haven’t panned out as we hoped, all of which might be unrelated to HTT lowering itself. All of these trials are also treating people with HD who are already showing symptoms and perhaps these folks are more vulnerable to potential side effects from these drugs. It’s important to note that none of these trials have given us a definitive answer as to whether HTT lowering in people with HD will improve symptoms or change the course of the disease. As the uniQure trial continues, we hope that the next data release might shed some light on this important question.

The VIBRANT-HD study began in early 2022 and was a long-awaited trial of a huntingtin-lowering drug, branaplam, that could be taken by mouth. On Monday, August 8th, we learned that dosing has been temporarily suspended at the recommendation of an independent committee that is monitoring the data from the trial. This decision was made because of signs that some of the participants taking branaplam may be experiencing new problems with their nerves, known as peripheral neuropathy. Let’s talk more about what happened and what’s next.

The HD gene and the quest to lower huntingtin

Huntington’s disease is genetic, meaning that it’s passed down in families from generation to generation. The genetic mutation that causes HD occurs in a gene called huntingtin, which produces a faulty RNA recipe, ultimately producing an extra-long huntingtin protein. This protein is believed to be harmful to brain cells, causing them to become sick and eventually disappear, and this leads to the many different symptoms of HD.

Over the past decade or so, novel approaches to treating HD have focused on a technique called huntingtin-lowering, which aims to decrease the amount of harmful huntingtin protein in the brains of HD patients. So far, the ones tested in people have been pretty invasive, requiring frequent spinal injections or brain surgery to deliver. Novartis, however, had recently begun a clinical trial of a huntingtin-lowering drug that could be taken once weekly, by mouth.

Branaplam and the promise of oral huntingtin-lowering

The story of branaplam and the VIBRANT-HD trial began with a different disease, known as SMA, which affects children. SMA is also genetic; it causes worsening muscle weakness in babies and young kids and is eventually fatal within just a few years.

Branaplam was originally developed as a genetic treatment for SMA. It is known as a splicing modulator – essentially this means that it can steer the remixing of the RNA recipe for the gene involved in SMA, and restore the function of the protein. In a fascinating twist of science, Novartis discovered that branaplam could also affect the RNA recipe for huntingtin, in this case leading to less huntingtin being produced.

In the summer of 2021, as more genetic treatment options became available for kids with SMA, Novartis made the decision to stop developing branaplam for kids with SMA, and to focus its efforts on adults with HD. This decision was supported by data in HD model animals, and very early safety trials of branaplam in healthy adults. Excitement built in the HD community around the possibility of an oral huntingtin-lowering treatment, and the Phase 2 VIBRANT-HD trial began in early 2022.

This week’s sad news

The VIBRANT-HD trial was planned to involve 75 people with early symptoms of HD, at more than 20 sites around the world. The main goals of the study are to test safety and the ability of the drug to lower huntingtin measured in spinal fluid. The plan was to test high and low doses of branaplam, each taken as a liquid once weekly for four months. Since early 2022, only the first cohort of participants had begun the trial. This was approximately 25 people, around 20 taking low dose branaplam and 5 taking placebo.

We learned today that the dosing in the trial has been stopped for safety reasons. We’ll get right to the point: branaplam was showing signs that it could be toxic to the nervous system. This was determined by an independent Data Monitoring Committee (DMC), a group of evaluators that has access to the data, long before the doctors, patients, or study sponsor (Novartis) know the outcomes. This is an important and standard practice in the vast majority of drug trials and it’s exactly for this reason – to keep participants safe in the event that problems arise.

The recommendation to suspend dosing in the study was based specifically on signs that branaplam might be causing damage to nerves outside the brain and spinal cord, known as peripheral neuropathy. Evidence from neurological exams, nerve conduction studies, and assessments of HD symptoms, as well as measurements of levels of a protein called NfL in the blood, all pointed to some concerns that some patients could be experiencing new nerve damage in their limbs.

What happens next?

In the immediate term, everyone participating in the trial will stop taking the treatment they were assigned. However, they will be asked to continue having their planned study appointments, which include blood and spinal fluid collection, and tests of nerve health. Essentially, the study will continue, but without branaplam or placebo, and participants will be monitored closely for other safety signs. This will be essential to understand as much as possible about branaplam’s effects on adults with HD.

There may also have been some people who were all set to begin participating in the VIBRANT-HD trial, at either a low or a higher dose – these folks will not begin the study. Current participants and doctors will stay “blinded” until the end of the study, meaning they still don’t know who was on drug or placebo.

What does this mean for branaplam…and huntingtin lowering?

Essentially, this trial suspension is a way to protect participants from further potential danger to their nervous systems. It also means that Novartis will need to take a step back, take the time to analyze and learn more from the data, and determine whether it would make sense to keep testing branaplam.

It might be that the drug is really not safe for people with HD, and moving forward isn’t an option. On the other hand, it might be possible to use lower or less frequent dosing, or it could be that branaplam may have affected some participants differently than others. This latter possibility is similar to how Roche will be running a new trial of the huntingtin-lowering drug tominersen in a specific group of people.

It’s a tremendous disappointment that branaplam looks much riskier than expected for adults with HD. This will of course be especially tough for the first brave trial participants in VIBRANT-HD. But the news affects everyone in the community who felt hopeful about the first oral huntingtin-lowering drug to be tested in people.

That said, this news is not reason to abandon hope in huntingtin-lowering – nor even in oral huntingtin lowering. Branaplam was originally designed to treat a different disease, and though it lowers huntingtin, there may be other reasons it is causing unforeseen issues, known as “off-target effects.” There is another oral huntingtin-lowering drug in clinical trials right now – it’s called PTC-518 and is being developed by PTC Therapeutics. Based on data published by the company, that drug may have more ideal drug properties, compared to branaplam. Importantly, PTC-518 shows more accumulation in the brain, compared to the rest of the body, and the brain is the primary treatment goal for HD. We look forward to updates from PTC after they digest the branaplam results, but we’re hopeful that their trial can continue, if experts feel it’s likely to be safe.

Gratitude and moving forward

Beyond these oral drugs, there’s a wide field of folks working on various approaches to huntingtin lowering, and ongoing clinical trials are being conducted by uniQure and Wave, with Roche’s next study in planning stages. There are also some important HD research conferences approaching this summer and fall, and there is sure to be exciting news to share from HD clinical studies and basic research laboratories worldwide.

There’s no doubt this is a tough day for the HD community, and for those of us hopeful for Huntingtin-lowering drugs to be an effective treatment for HD. But, as we often say, science is cumulative, and if we do it right, even failures in the clinic can teach us more than we knew before we started the trial.

The entire community owes the participants in the VIBRANT-HD study a huge debt. They rapidly signed up for the study, and their participation enabled us to get to this point – disappointing as it is – as quickly as possible. Their selfless contribution will enable the design of the next study to take into account the lessons learned in VIBRANT-HD, and get us closer to a day when we have effective treatments for HD.

uniQure is a company specializing in gene therapy, and they have been working on an experimental drug for Huntington’s disease (HD), called AMT-130, that is delivered via brain surgery. This is an unprecedented genetic approach to treating HD, and safety is the top priority for the first human trials. A press release and public presentation on Thursday June 23rd announced 12-month data on safety and huntingtin-lowering, from the first cohort (group) of 10 people with HD to undergo the surgery. HDBuzz also had the opportunity to speak with Dr. Ricardo Dolmetsch, President of Research and Development at uniQure, to get some additional clarity on what was shared. Overall, the drug and surgery were well tolerated, with no major safety issues arising so far. It can be difficult to interpret huntingtin-lowering data from such a small group, but what’s there so far looks like it could be promising – let’s explore what it means and what’s next for this study.

The first gene therapy for HD

Let’s begin with a refresher on the basics of this trial. Gene therapy is a technique that aims to permanently modify the core instructions from which living things are built. There are different targets and different methods for transporting such drugs to parts of the body and brain, but the key point is that gene therapy aims for permanence, a one-and-done delivery, to treat a genetic disease at its roots. Most HD gene therapies are focused on a technique called huntingtin-lowering, which targets the huntingtin gene or its genetic message molecule, RNA. The aim is to switch off the gene and decrease the amount of harmful huntingtin protein that is madebuilds up in the brain, with the goal of slowing the worsening symptoms of HD.

uniQure is developing an HD gene therapy called AMT-130. They are using an approach where a piece of man-made genetic material is packaged inside a harmless virus and delivered directly to the part of the brain that is most affected by HD, the striatum. This requires a single surgical procedure in which minuscule holes are made in the skull and tiny needles are used to inject the virus into six different locations deep in the brain. The drug spreads into many brain cells and sets up little factories for producing a type of genetic micro-message that tells the cell to make less huntingtin protein.

The state of uniQure’s HD clinical trials

uniQure spent several years testing their drug in different lab models and animals, including pigs that have the HD gene. Then, when it looked like they could safely achieve huntingtin-lowering in a large animal brain, they embarked in 2020 on the first trial in people, known as HD-Gene-TRX1. So far, 36 people are enrolled in different cohorts (groups) of this trial in the USA and Europe, some receiving a low dose of AMT-130, some receiving a high dose, and some receiving an imitation surgery, in which no needles are used and no drug given but the tiny holes are made.

Last week’s press release and an investor-focused presentation from uniQure shared some data, from just the first cohort of 10 participants with HD. 6 of these individuals received the low dose of AMT-130, and 4 were in the “control” group that had imitation surgery. In addition to showing that the drug and procedure were safe and well-tolerated, uniQure was able to share huntingtin-lowering data from 7 of the participants, 4 in AMT-130 group and 3 in the control group.

The very small numbers of people mean that the data is variable and should be interpreted with caution. That said, there may be reason for excitement, even with such a small group.

What was shared in the press release?

The June 23rd press release shared basic data on the side effects of the surgical procedure, levels of huntingtin after 1 year, and a protein called NfL that can act as an indicator of brain health. Essentially, what they shared addresses safety first and foremost, followed by a “biomarker” of how brain cells might be reacting to the treatment, and a measure of whether the drug is acting biologically in the way it’s meant to – this is known as “target engagement.”

Safety & Tolerability

This is the simplest piece to interpret and is solidly good news. The 10 participants were followed closely over the course of 1 year, and the main side effects they experienced were related to the surgery, which was overall very well tolerated. The surgery can take most of a day, and one person had a blood clot from being immobile for many hours, which resolved soon afterwards. Another person experienced delirium after the surgery, a period of serious confusion that happens sometimes after anesthesia, and this also resolved quickly. Those were the most serious side effects; other examples of minor ones were headaches after the surgery, and pain or dizziness after lumbar punctures to take samples of spinal fluid.

Measurements in spinal fluid

The 10 participants in the first cohort had lumbar punctures before having the surgery (“baseline”) and then 1, 3, 6, 9 and 12 months later. This was to allow uniQure to measure changes in levels of huntingtin as well as other biomarkers, like NfL, that can help to give a picture of brain health.

* Biomarkers: Temporary increase in NfL

A biomarker is something in the body that can be measured to give us a picture of an aspect of a person’s health. For a neurodegenerative disease like HD, an ideal biomarker changes reliably as things worsen, and reverts with treatment. NfL, which is released by sick brain cells, tends to increase as HD progresses, so it is increasingly being measured as part of human clinical trials. However, a short-lived increase in NfL can also indicate different types of stress on brain cells, such as that caused temporarily by an invasive brain surgery. As expected, the HD-Gene-TRX1 participants who received the drug had an increase in NfL that went up right after the surgery and slowly returned to baseline levels. For those who had sham surgery and no needles or drug, NfL levels stayed around the same over that time period.

* Target engagement: decreased huntingtin levels

The goal of uniQure’s therapy, from a biological standpoint, is to target the genetic “message” created by the huntingtin gene, so that less huntingtin protein is made in brain cells. So for AMT-130, “target engagement” means lower levels of huntingtin. They were only able to make accurate before-and-after measurements in a subset of participants, but despite this roadblock, it already looks like AMT-130 may be lowering huntingtin protein. For people who received the drug, they found that huntingtin levels dropped over time, and by 12 months they were about 50% lower on average. The people in the sham surgery group had lots of variability in the levels of huntingtin in their spinal fluid but looked fairly steady. Again, the numbers are way too small to talk about statistical significance, but overall it looks like the drug is doing what it is designed to do.

The trials and tribulations of measuring huntingtin

Ideally we would have a clever way to look directly in the brain at huntingtin levels before and after treatment, and scientists are working on tracers which would allow us to do just that, but these are not ready to use in drug trials just yet. Instead, scientists measure the very small amounts of huntingtin protein found in spinal fluid as a proxy, and these measurements are a technical challenge for the entire field of HD research. Of the 10 people in this part of the uniQure study, the researchers were only able to get reliable huntingtin-lowering data from 7; 4 people who received the drug and 3 who received the sham treatment. This means we are looking at data from a very small number of people so, whilst things look to be going in the right direction, we should still be cautious.

Another consideration is that uniQure’s drug lowers both healthy and harmful huntingtin, based on this data, by around 50% in people who received the low dose of AMT-130. Questions came up in the public presentation around whether longer exposure or higher doses could lead to “too much” lowering of huntingtin, but this seems unlikely for several reasons.

The work that uniQure have published in animal models shows that higher doses of the drug are safe and well tolerated over the course of several years. In people, the data so far show the levels of huntingtin getting lower and lower over time, but uniQure expects the lowering to level off after 12 months, as they have seen in their animal model experiments. They also show that higher doses of the drug don’t lower huntingtin levels much more than low doses; instead, the drug is able to spread to more parts of the brain, so the same level of lowering is seen in more areas, which they think will be beneficial.

Finally, there are several trial participants in the USA and Europe who have already received high doses of AMT-130, and none of them have had major dangerous side effects thus far.

So what’s next for AMT-130?

Although this early data is encouraging that AMT-130 is doing what scientists hoped – lowering huntingtin levels – there is still a long way to go before this could be a drug to treat HD. A number of scenarios are possible, all of which hinge on the outcome of the results uniQure is due to publish in the second quarter of 2023.

In the best case and probably unlikely scenario (but we can hope!), the next data release will have extremely positive findings, which could prompt uniQure to pursue accelerated approval of the drug to start treating people with HD as soon as possible. What is more likely, but still wishful thinking at this stage, is that the next data update holds up the tentative conclusions we have drawn so far – the drug appears safe, engages the target by lowering huntingtin and, perhaps, might show some indications of improving symptoms or slowing down the progression of HD. In such a scenario, uniQure would likely launch a much larger phase 3 study with over 100 patients enrolled and divided into control and treatment groups, to determine in a larger population whether the drug is really doing what the scientists hope – slowing or halting the progression of HD.

However, we must prepare for the possibility that the results in 2023 are not what we hope. One possibility is that the drug continues to be safe, but that huntingtin levels are not lowered. This may not be as bad as it seems, it could be that it takes some time to see a measurable effect of AMT-130, we just don’t know what to expect at this stage. The worst case scenario is that signs of HD in people who receive the treatment could appear to progress faster – similar to the results of the tominersen trial. In that case, uniQure would need to go back to the drawing board.

All that speculation aside, uniQure are taking concrete steps to improve upon the surgery, as well as planning for access to AMT-130, should the results of this trial prove favourable. One drawback for this “one-shot” therapy is that the procedure itself takes all day. In a third cohort of patients, uniQure are planning to test a much shorter version of the surgery which would only take half a day to complete.

All in all, uniQure’s preliminary safety and huntingtin-lowering results are encouraging. We are grateful for the brave participants in this unprecedented gene therapy trial, and eagerly await the next data release.

Scientists have developed a new model that maps out the different stages of Huntington’s disease (HD) in detail. Using artificial intelligence approaches, the researchers were able to sift out information from large datasets gathered during observational trials contributed by Huntington’s disease patients. A team of researchers from IBM and the CHDI Foundation have published a new model of HD progression in the journal Movement Disorders that they hope will improve how HD clinical trials are designed in the future.

Predicting the progression of HD symptoms is complicated

HD is caused by an expansion in the huntingtin gene which leads to the production of an expanded form of the huntingtin protein. Studies of lab models of HD as well as people carrying the HD gene, show that having the expanded gene and making the expanded form of the protein causes a cascade of problems. Starting with small molecular changes, people with HD will eventually end up experiencing a range of different symptoms related to thinking, movement and mood that get worse over time.

Symptoms of HD typically start to show between the ages of 30 and 50, but a number of factors influence when this happens. We have known for a long time that people with bigger expansions in their huntingtin gene tend to get symptoms earlier, healthy lifestyle choices like a balanced diet and regular exercise can delay symptom onset, and other so-called genetic “modifiers” can also influence how early the disease might affect a gene carrier.

However, there’s still a lot we don’t understand about how Huntington’s disease progresses over time and how the symptoms get worse. To try and tackle this problem, scientists from around the world have run numerous observational trials and natural history studies where patients’ symptoms, biomarkers, and other measurements are monitored over time. These include PREDICT-HD, REGISTRY, TRACK-HD, and Enroll-HD. Together these studies have generated very large datasets which comprise more than 2000 different measurements recorded from 25,000 participants. This is tons of really helpful data, all made possible by the dedication of HD families to participating in these trials.

Machine learning helps us learn more about HD progression

Scrutinising all these datasets at once can help scientists spot new patterns and make novel conclusions but doing this type of analysis manually is extremely laborious and challenging. This is where the clever computer scientists come in! Scientists are able to use cool new methods to get the computers to look at all the data at the same time using special types of programs often referred to as artificial intelligence or AI.

One commonly used AI approach is called machine learning. This type of AI software becomes better at making predictions of certain outcomes by building models from training data sets which it uses to “learn” without being explicitly programmed to do so. Machine learning is a field in its own right in biomedical research but also has lots of different applications for things like email filtering and speech recognition.

IBM and CHDI researchers used machine learning approaches to build and test a new model to understand how HD progresses and to categorise different disease stages. The model was then tested against a number of different measurements commonly collected and compiled in HD research that track disease progression, including the Unified Huntington’s Disease Rating Scale (UHDRS), total functional capacity (TFC), and the CAG-age product, also called the CAP score.

The new model defines 9 states of HD, all specified by different measurements that assess movement, thinking, and day-to-day function. These states span from the early stages of the disease before motor symptoms begin, all the way through to the late-disease stages that have the most severe symptoms. The model was able to predict how likely participants in the studies were to transition between states as well as how long participants spend in the different phases of HD. While other studies have determined that the entire disease course occurs over a period of about 40 years, this is the first time researchers have predicted the expected amount of time HD patients will spend in each of the 9 states that were described in the new model.

New models of HD progression will hopefully inform clinical trial design

Having this handy new 9-state model of HD progression can help scientists and clinicians learn more about the different stages of HD and the timeframes it takes people with HD to move from one state to the next. With this information in hand, the researchers at IBM and CHDI believe this could help select the best-suited participants for particular HD clinical trials, identify robust biomarkers for monitoring how the disease progresses, and also help design better clinical trials.

This is an exciting step forward for HD research and we look forward to learning more about other AI applications in HD research as novel approaches are designed and this exciting field of science matures further.

For those who were following the live tweets from HDBuzz about the CHDI HD Therapeutics Conference or tuned in to the HDSA Convention, we may have caught your attention with the new HD staging system. And if you missed it, you’re in luck! The publication detailing this new classification system, how it’s used, and its benefits is hot off the press. Let’s see what they have to say.

Tracking disease progression – time for an update

Until now, people with Huntington’s disease have been categorized primarily based on their clinical symptoms. Physicians watch a patient walk, perform hand movements, or ask them to think of different words. A mix of tests related to thinking, movement, and mood helps medical doctors gauge where individuals are in the course of their disease.

Diagnosing patients and categorizing their disease stage with clinical symptoms has been going on since the 1800s, long before scientists identified the gene that causes Huntington’s! However, this type of categorization of people with HD is quite dated, and it doesn’t always capture the full picture.

Currently, “pre-symptomatic”, “prodromal”, or “premanifest” patients all fall into a single category. These are individuals who are gene positive for Huntington’s but have no clinical signs of the disease – or at least no movement symptoms, which are the most common way HD is diagnosed. This category can include individuals from birth until about the age of 40. This is a huge pool of patients over a long period of time!

As research around Huntington’s disease advances, we’re learning a lot about very subtle changes that occur even decades before any clinical symptoms are apparent. This has prompted a team of researchers, known as the Huntington’s Disease Regulatory Science Consortium (HD-RSC), to develop a more sophisticated scoring system.

How the new system was developed

The Huntington’s disease Integrated Staging System – HD-ISS – combines information from brain scans, clinical tests, and day-to-day abilities to determine where HD patients are in their disease. This new scoring system takes into account the entire life of the individual, classifying every age, from birth to death.

To develop this new scoring system, the HD-RSC team used data from the Enroll-HD, TRACK-HD, IMAGE-HD, and PREDICT-HD trials, all observational studies which follow people in HD families over time. A big thank you to everyone who has or is sacrificing their time to participate in these trials – you’ve made the creation of this new scoring system possible! They also consulted a variety of different groups, including patient advocacy groups.

HD-ISS stages

In a recent talk to the HD community at the HDSA Convention, Dr. Sarah Tabrizi, who is leading the charge on the HD-ISS, likened the new system to what is used in cancer. Cancer is classified into stages based on the size and spread of the tumor. The HD-ISS will work in a similar way, categorizing patients into 4 stages – stage 0 through 3 from no impairment (birth) through severe impairment (end-of-life). Each stage is sequential, meaning a patient will experience components of the previous stage to be classified into the following stage. The staging system is also progressive, meaning patients will always begin at stage 0 and progress through to stage 3.

Stage 0: HD gene present, no other changes

An individual who has been genetically diagnosed with HD (40 or more CAG repeats), but has no detectable changes associated with Huntington’s disease. This stage begins at birth and tracks an individual until they have some sort of detectable change.

Stage 1: HD gene present, biomarker changes only

Individuals move into this stage when there are detectable changes in biomarkers known to occur with Huntington’s disease. Based on data from thousands of participants in clinical studies, the biomarkers they chose were the volume of 6 specific areas of the brain using MRI. Changes in these areas are known to decrease in people with HD as cells in the brain are lost.

Stage 2: HD gene present, biomarker changes, and clinical signs

This stage begins when a patient shows clinical signs of Huntington’s disease. The new scale focuses on motor and cognitive changes, as measured with movement tests and a thinking task that asks people to pair numbers with symbols.

Stage 3: HD gene present, biomarker changes, clinical signs, and difficulties with daily function

The last stage begins when a patient experiences functional decline, such as difficulty carrying out day-to-day tasks. Additionally, stage 3 is broken up into mild, moderate, and severe functional decline. Mild stage 3 includes individuals that may take a long time to do routine tasks, but don’t require assistance. Moderate stage 3 includes those who require assistance with some routine tasks. Severe stage 3 includes those who require assistance with all routine tasks.
The amount of time spent in each disease stage will differ from person-to-person. How quickly an individual progresses through each stage is variable, but strongly depends on age and CAG repeat length.

Why we need the HD-ISS

The HD-ISS will help standardize clinical research by categorizing patients in a more predictable way. This will allow clinicians conducting clinical trials to more quickly select research participants for studies who are likely to have a similar disease course or respond similarly to a treatment. Standardizing the categorization of different stages of Huntington’s disease, particularly between birth and the onset of clinical symptoms, is necessary to help the field move toward testing drugs earlier, before clinical symptoms are apparent. Many people think the most effective time to treat HD will be before a person even gets sick, so having a system in place before these trials are designed is critical.

Also, these clear delineations of patient populations will make it easier for researchers to compare data across studies – something that has been a bit muddy in the past because of loose definitions of disease stage. Comparing data across studies will allow researchers to gain as much information as possible from each trial, which will decrease the amount of time it takes to get to our end goal – a treatment for HD.

How will the HD-ISS affect research and care?

It’s important to note that the HD-ISS is focused on research – it aims to streamline the design and recruitment of clinical trials. This newly published system doesn’t mean that doctors who treat HD will suddenly be categorizing their patients. In fact, that’s not necessary to develop an individualized treatment plan based on a person’s current symptoms. But once therapies to slow disease progression become available, the system could help guide treatment decisions.

Another key message is that a more rigorous system for trial selection doesn’t mean the therapies being tested couldn’t benefit others in a different stage of HD. This is first and foremost a way to make trials smoother and data easier to interpret, which has the potential to speed the drug pipeline by leaps and bounds.

Implementation of the new HD-ISS scoring system should be straightforward for the Huntington’s community. In fact, the upcoming PTC Therapeutics trial for PTC-518 will be the first to use the HD-ISS. Most of the measurements collected for this staging system, like CAG repeat length, brain imaging, and functional capacity scores, are standard in Huntington’s disease research. Standardizing the way various stages of Huntington’s disease are classified is a clinical advancement that will help organize trial selection and data interpretation as we advance toward treatments for HD.