We’re back for day 2 of the CHDI Huntington’s Disease Therapeutics Conference! We’re kicking things off with some exciting talks on genetic modifiers and learning how we can advance them toward therapeutics for HD.

Advancing Genetic Modifiers Toward Medicines

Today’s session is all about genetic modifiers – genes that contribute to the age of disease onset – which were discovered through massive genetic studies that looked at levels of every gene in someone with the gene for HD. This let researchers identify genes that correlated with earlier or later HD onset. Genes related to somatic instability were identified as modifiers in large genetic studies, called GWAS, or genome wide association studies. Researchers are advancing GWAS data towards therapeutics. This wouldn’t be possible without the collaboration between scientists and the HD community. Super exciting!

Seung Kwak: It’s Not All About Somatic Instability

Our first speaker in this session is Seung Kwak from CHDI, who is talking about genetic modifiers that aren’t related to somatic instability. These modifiers can change disease onset by 7-10 years (that’s a lot!), but they don’t seem to affect somatic instability.

Seung and others are building a pipeline to help them identify more non-somatic instability-related modifiers and figure out how they alter when symptoms begin. This will help identify new pathways in HD, diversifying the possible molecules researchers could target with new therapeutics.

Once they identify these genes, they’ll try to figure out which characteristics of HD those genes control, like rate of disease progression or motor symptom onset. Seung thinks different modifiers might work throughout the course of HD as it progresses, contributing to various aspects of disease onset. By scrutinising which genes might contribute to which timepoints in HD progression, we’ll have a better idea of when we could or should intervene with therapeutics that target each step.

Seung states that, “we’re not alone”, highlighting that other diseases are similar to HD, like SCA1, another neurological disease also caused by expanding CAGs. He stresses the importance of learning from these diseases, which can help advance what we know about HD.

By leveraging what we know about HD to identify modifiers, e.g., striatal neurons are the most affected cells in HD, we can diversify how we identify modifiers and diversify what we learn and the types of therapeutics we could make. This could help determine if a combinatorial approach will be best.

Marcy MacDonald: Effects of The “Other” Modifiers

Up next is Marcy MacDonald, who was a key member of the team that identified the genetic mutation that causes HD in 1993. She’s dedicated her career to further understanding HD to help get us closer to a treatment. She’ll be sharing her team’s work on genetic modifiers of HD. She starts by highlighting GeM-HD, a massive genetic study that first defined some of the genetic modifiers of HD. Marcy shared that the GeM-HD study wouldn’t have been possible without the amazing collaboration we have between HD researchers and the HD community.

She reminds us that HD symptoms are the result of complex events at the molecular level. We have only just begun finding out what influences symptom onset, and some genes are already being targeted! But there are still discoveries to make as we get more and more data.

Many of the modifiers we have already heard about at this conference are involved in mismatch repair – an important process in looking after our DNA. These are the same genes that participate in somatic instability. However, there is almost an equal number of modifiers that have entirely different biology and which really warrant further study to figure out how they influence when HD symptoms begin.

Marcy is sharing data that pulls out modifiers at different disease stages. Interestingly, the non-mismatch repair modifiers seem to influence disease earlier. This means if we could perhaps find a way to target these “other” modifiers, we could find ways to intervene very early in disease.

She also compared genetic modifiers across datasets. While there is some overlap, there are some modifiers unique to each dataset. However, multiple datasets do show DNA repair genes as common hits. She highlights that these differences are important to understand. Some modifiers influence movement symptoms of HD, whereas others seem to impact thinking symptoms of HD. Maybe this means modifiers underlie different aspects of HD biology.

Targeting those aspect-specific modifiers could help scientists develop future treatments tailored to treat different types of HD symptoms at different timepoints in the disease. This could give HD clinicians the option for precision medicine approaches to treat folks in the future. Marcy suggests that there could be modifiers specific for various biological processes, e.g., initiation of expansion, rate of expansion, cell-specific effects, cell toxicity, and response to neuronal loss. It would be fantastic to have targets against each one of these unique aspects of HD!

Further, she also urges the community to not think solely about exactly which cells are lost over time in HD, but also about what circuits to which these correspond. The loss of specific circuits is what underlies different HD symptoms in her opinion.

Now she’s diving into specific non-DNA repair modifiers, starting with one called Lig1. Mice that model the genetic changes in Lig1 from GWAS have been made so researchers can deeply study how this gene influences HD.

Another modifier she mentioned is RRM2B, which is more involved in motor symptoms and less involved in cognitive symptoms. RRM2B helps keep mitochondria (the cell’s powerhouse) healthy under stress conditions. Marcy is sharing lots of details about the exact genetic changes that were found in these GWAS. She highlights that 12,000 people were needed to see these changes related to RRM2B. Highlighting how important it is to have HD families contribute to research!

The next modifier on Marcy’s list is the CAA sequence that sometimes interrupts the CAG repeat stretch within the huntingtin gene. Research tells us that this is the strongest modifier of age of symptom onset, which can delay the onset of HD symptoms by up to 10 years. She highlights that the CAA interruption doesn’t seem to influence CAG instability, but does influence HD symptoms.

So how does it do that? We don’t know for sure. Marcy thinks it may act indirectly to affect instability or act directly on certain types of brain cells, influencing their vulnerability.

In this tour de force talk, Marcy wraps up by summarizing that different symptoms happen at different times in HD. Genetic modifiers identified in GWAS can help us better understand why this is and develop interventions to help alter clinical signs and symptoms of HD.

Margaux Hujoel: Somatic Instability Lessons From 700,000 People

Our next speaker is Margaux Hujoel from Harvard University. Her talk will go through what she’s learned about the causes and consequences of somatic instability from genetic data from 700,000 people who donated samples, like blood or spinal fluid, to research. To understand genetic variations in HD and other diseases, we need massive datasets from thousands of people to be sure of the findings. As genome sequencing technologies have advanced dramatically in the last few decades, we now have access to HUGE datasets – very exciting.

She starts by summarizing the concept that HD is driven by somatic instability, the perpetual expansion of the disease-causing CAG repeat. However, researchers don’t yet understand the nitty gritty of why instability is so important in HD.

Margaux is stepping back from the huntingtin gene, and studying how somatic instability happens throughout the entire genetic code (genome) to see what lessons can be learned through a broader lens. Other diseases are caused by expanded repeats so we could learn more about HD by studying them.

Two such diseases are Myotonic Dystrophy and Fuch’s Corneal Dystrophy, an eye disease. Research into these diseases show that new cases arise through repeat instability that pushes a repetitive DNA sequence to a length that causes disease, very similar to what happens in HD.

Around the globe, there are various biobanks – places that collect tissues and fluids donated by people living with diseases. Using samples from these biobanks, Margaux and her team are learning more about somatic instability that has relevance across diseases.

There are some technical challenges with analyzing long repeats in the DNA, but Margaux’s team has come up with a work-around and found that the vast majority of expansions happen in only a handful of genes, helping to narrow down what we should focus on.

There are 18 different places in the human genome that are sensitive to somatic CAG instability, 9 of which are known to cause disease. Samples in the biobank from related people lets Margaux and her team map genetic changes in the genome over multiple generations. She found CAG expansions tend to expand more often than they contract and expansions happen more frequently with longer CAG repeat lengths. This isn’t new for HD researchers, but it’s interesting for us to know that this phenomenon isn’t unique to HD and happens across the genome.

They also looked at how expansions differed between different types of tissue, like blood vs brain tissue. This matters as we need to know which biofluids or tissues might be best to track expansion, and to measure changes to expansion in forthcoming clinical trials which aim to slow down expansion.

Margaux showed data for various diseases where the repeat expansions were more likely in the germ line (egg and sperm) than blood, and vice versa. This suggests that cell type specific differences in CAG repeat diseases may not be the same, BUT cell type specificity does seem to be a common feature.

Another common feature across these diseases is that similar genes contribute to repeat instability, like modifiers related to DNA repair, like MSH3, PMS2, and FAN1 – all genes that are being heavily scrutinised in HD for the role they play in somatic instability.

Margaux suggests that we can apply some of her research to HD, cautioning that somatic expansion in blood may not match what’s going on in the brain, but it could still be an interesting biomarker for therapeutics aimed at controlling expansion. The field is working hard to find biomarkers to track somatic expansion as potential treatments work their way toward the clinic. However, we can’t take brain samples throughout clinical trials, so blood could be a way to see if such treatments are having the effect we want.

If blood samples turn out not to be a good surrogate for such therapeutics, we may have to rethink our strategy. This challenges current approaches in HD research, but that’s what conferences are all about! Challenging what we know, getting people to think about things in different ways, and advancing HD research with a broad perspective.

Aaron Gitler: Modifier Lessons From Other Diseases

Up next is Aaron Gitler, who works on ALS (Lou Gehrig’s disease) and will share findings from his own work that he thinks could be relevant for HD. Specifically, this involves his work on genetic modifiers.

ALS can be caused by changes to a gene called TDP-43. Like huntingtin, this can cause the build up of protein clumps associated with disease. Interestingly, this gene was also recently implicated in HD.

Aaron found a gene, called ATXN2, that suppresses protein clumps of TDP-43. While ATXN2 seems to be a modifier of ALS, it also causes a disease, called spinocerebellar ataxia 2. He found that in some ALS cases, there is a genetic expansion of CAG repeats in the ATXN2 gene. Interestingly, he’s found that different CAG repeat lengths in ATXN2 cause different disease features in different cells. Quite a complex system!

In mice that model ALS, when Aaron reduces levels of ATXN2, the mice live much longer lives and disease features in cells of the brain seem to disappear. This suggests that ATXN2 could be a good target for ALS therapeutics.

His work suggests that there are bits of genetic information contained in proteins when people have disease that aren’t there in people who don’t have these diseases. The inclusion or exclusion of these pieces of genetic information happens through a process called splicing.

Through this work, he may have identified a genetic cause of TDP-43 disease that could be targeted for therapeutic benefit. He suggests that similar biological mechanisms may be at play in HD, particularly given the newly published association between HD and TDP-43.

Julien Marnet: Hunting For The Master Switch In HD

Our last speaker of the day is Julien Mamet, who works at Core Biotherapeutics, a company focused on developing therapeutics that target genes called “transcription factors” – genes that act like master regulators to control the levels of lots of other genes.

Julien looks at large datasets, mapping how genes within certain cell types connect in a hierarchical way to regulate each other. Doing this in cells with and without HD allows him to identify differences and figure out how to target master regulators within these hierarchical networks. Julien reminds us that not all transcription factors are equal, so lots of effort is put into understanding which of these master regulators may be dominant. They call these the “core” components of the network. In disease, these “core” master regulator genes are thought to drive disease.

They’re working to integrate lots of different datasets to build a library of networks and identify cores within those networks. This will help them identify targets that they can design therapeutics against that they think could improve disease signs and symptoms.
For HD, they’re starting to build these networks using datasets from various cell types in the brain. From these networks, they’ve identified core genes called “HOX”. HOX genes are particularly strong in neurons that are vulnerable in HD.

In HD, these HOX genes seem to alter thousands of genes that are necessary for the proper function of brain cells. Julien finds that these HOX genes are core genes within the networks of early and late stages of HD. Julien suggests that because HOX genes are unchanged in brain cells not largely affected by HD, they should be safe to target with therapies. Interestingly, they see something similar for other diseases caused by CAG repeats, suggesting a possible therapy that targets HOX could be effective for more than HD.

That’s it for us today! Stay tuned for updates from the last day of the Therapeutics Conference to learn more exciting updates on Huntington’s disease research!

Hello from Palm Springs! The HDBuzz team are here and ready to report on all of the exciting science that we are going to hear over the next 3 days from HD experts who have travelled from all over the world to be at CHDI’s 20th Annual Huntington’s Disease Therapeutics Conference. Get ready to follow along for some exciting Huntington’s disease research over the next 3 days!

Clinical Trial Updates

Our first set of talks are updates from pharma companies that have ongoing clinical trials.

PTC Therapeutics – PIVOT-HD Testing Votoplam

Up first is Amy-Lee Breadlau from PTC Therapeutics with an update on votoplam, formerly PTC-518. Votoplam is a HTT-lowering drug that’s taken as a pill. The idea is that by lowering the disease-causing protein, signs and symptoms of HD will be reduced.

Amy-Lee started by sharing the fantastic news that PTC has an exciting new collaboration with Novartis, a massive drug developer. PTC will complete the ongoing PIVOT-HD trial, but Novartis will be in charge of all future clinical trials, like their planned Phase 3.

So far, people in the PIVOT-HD trial have been taking votoplam for 12 months. They were really interested in knowing if people who have been on the drug this long have positive changes in biomarkers – biological metrics that track with HD progression. The most reliable biomarker we have right now is neurofilament light, or NfL. We know that levels of NfL increase as HD progresses. Excitingly, Amy shows that levels of NfL remain steady for people who have been on votoplam for 12 months.

She’s now showing super exciting data that suggest there is improvement in clinical measures in people who have been on the drug for 1 year. At the end of the day, this is exactly what we want! A drug that improves clinical signs of HD is a drug that’s working against HD!

The final results from PIVOT-HD are expected to be released this summer. We’ll certainly keep you updated as we learn more!

Roche – GENERATION-HD2 Testing Tominersen

Up next is Peter McColgan from Roche who is sharing an update on their Huntington’s disease portfolio. Their largest trial has been GENERATION-HD1 for their HTT-lowering drug tominersen. While that trial wasn’t successful, it provided the data for their ongoing GENERATION-HD2 trial that is testing tominersen in a more specific group of people living with HD.

The big news that Peter is sharing today is that GENERATION-HD2 is fully enrolled. They’re active in 15 countries at 70 sites and they’re hoping to complete the trial at the end of the year.

Roche has an active collaboration with the HD Regulatory Science Consortium to share the data that they’re collecting. Roche is also sharing natural history data and data from the GENERATION-HD1 trial from people who weren’t on the drug. This type of data allows researchers to understand how HD normally progresses as people live their day-to-day lives and age. This valuable information will be open to researchers, and will help us design better trials.

Roche also has a collaboration with CHDI to better understand the biomarker NfL. Their goal is to understand if NfL is more than a biomarker and could be used as a diagnostic test for HD. Using NfL as a diagnostic test could help give us information about where people are in the progression of disease. This could help tailor future drugs and help customize care plans based on disease stage.

They’re using multiple datasets, from Enroll-HD, HD-Clarity, Track-HD, and Track-On, to see how NfL changes over time. Collectively, these datasets give them samples from almost 7,000 people living with HD!

We can’t overstate how important these datasets are to the HD scientific community. So to everyone who participates in these observational studies – THANK YOU! YOU are truly changing the face of HD research! With your contribution, HD scientists are learning more about this disease every day, getting answers to questions that will get us to a treatment. If you’re interested in learning more or contributing to HD research, you can visit the Enroll-HD website.

Wave Life Sciences – SELECT-HD Testing WVE-003

Up next is an update from Wave Life Sciences on their HTT-lowering drug WVE-003 being tested in their trial SELECT-HD. This drug is unique because it specifically targets the expanded copy of HTT that causes HD. There are advantages for specifically targeting the expanded copy of HTT.

Wave also thinks that targeting the expanded copy will have an influence on somatic instability, the perpetual expansion of the CAG repeat within the HTT gene. While this would be super cool, we don’t yet have data to show that WVE-003 can actually impact somatic instability.

Wave did show that there’s a slowing of brain atrophy for people who are taking WVE-003. They hope to use this measure in future clinical trials as a readout of clinical outcomes.

However, we’ll have to interpret any data around brain atrophy carefully in context with biomarkers. Looking at brain atrophy alone can’t really tell us if HD is improving because other things could be at play here, like brain swelling. If a drug is causing inflammation of the brain, that could look like the brain is shrinking less, but doesn’t necessarily mean a drug having a positive effect.

But if there are biomarkers also suggesting that the drug is improving biological measures of HD, that would be a fantastic thing! We’ll have to interpret any data around brain atrophy carefully as we learn more and as WVE-003 progresses through the clinical trial pipeline. Wave is hoping to move forward with a Phase 2/3 study by the end of this year. We’ll keep you updated as we learn more!

UniQure – Testing AMT-130

Our last speaker in this session is David Margolin from uniQure sharing an update on AMT-130, a HTT-lowering gene therapy delivered via brain surgery. His focus today is on their recent alignment with the FDA on a path to accelerated approval for AMT-130.

AMT-130 is a drug delivered by brain surgery which lowers both the regular and toxic forms of huntingtin. Their drug hits right at the start of the huntingtin message molecule which means they also expect the toxic fragment form of huntingtin to be lowered too.

UniQure have applied to the FDA for RMAT – Regenerative Medicine Advanced Therapy Designation. This application was successful! This is important because it reduces the time it could take AMT-130 to get to market by several years. Obviously, this is very important for all HD families! UniQure continue to be in discussions with the FDA about exactly what data they will need for their drug to be approved on an accelerated time frame.

UniQure are planning to use natural history data to work out how well their drug is working. This means they will be comparing folks in their study against what is expected on average for people with HD who are the same age and so forth, but who didn’t receive the drug. This is a bit different to having a placebo control which is what companies typically use.

One of the big things that the FDA agreed on with uniQure is the use of cUHDRS as a metric for how well their drug is working. cUHDRS is a combo of lots of different measures about all kinds of signs and symptoms of HD. It is thought to be better than just using one measure as each has various caveats. However, when used in combination, these caveats can be weeded out and we can work out pretty quickly if the drug is REALLY working.

Further, the FDA also agreed to consider levels of NfL in spinal fluid as supportive evidence that AMT-130 is working. NfL typically goes up over time in people with HD. So, NfL levels going down or holding steady is good news for brain health for people with HD.

The fantastic news is that we now have agreement between the FDA and HD drug hunting companies about exactly what metrics and measures will be expected to show a drug is working well enough and is safe enough for the FDA to approve a drug.

Connecting The Dots: HTT Biology From The Lab To The Clinic

Our next session focuses on what we are learning in the lab about HD biology to inform clinical trials.

Longzhi Tan: Genetic Architecture

First up is Longzhi Tan from Stanford University, sharing his work on the architecture of genetic material and how HD influences its shape and where that genetic material sits in the cell. Genetic architecture sounds super cool! But what exactly is it?

We have a lot of genetic material that makes all of us unique, and where it sits within the cell matters. The DNA inside each cell of our body is 2 metres long!! To fit inside each tiny cell, it must fold and compress to be squeezed in. Tan is interested in studying exactly how the DNA is organised in cells and where each gene might be found.

Quite surprisingly, Tan can determine different types of cells just by where the DNA is sitting inside the cell. How DNA is organised and where it sits in the cell changes throughout life.

Now he’s looking at how HD affects the architecture of genetic material in mice that model the disease. He’s showing the crowd the very first 3D map of what the genetic material looks like in cells from HD mice. HD causes drastic changes, specifically in cells that are vulnerable in HD. Tan shares that he thinks these changes are leading to a loss in cell “identity” – genes that make certain cell types what they are.

Tan is also looking at how genes that control somatic instability might affect genetic architecture. Specifically, he looked at the modifier gene Msh3. When Msh3 levels are lowered in HD mice, it seems to correct the genetic architecture changes caused by HD. Very snazzy!

The take home message here is that targeting Msh3 in different HD models could be good for restoring many of the hallmarks of HD back to normal. This type of really detailed analysis is supportive that Msh3 is a good target for scientists to be working on to try and make new medicines.

Kejia Wu: Computer-Designed Proteins

Up next is Kejia Wu from University of Washington, in Seattle. She’s a recent PhD graduate from the lab of David Baker, 2024 Nobel Prize recipient. Her research tries to design new types of proteins to do specific jobs. This work uses all kinds of specialist deep-learning and AI-guided tools to try and think up new designs.

Kejia is interested in targeting floppy bits of protein molecules. Turns out these floppy regions are really important for all kinds of biology but were traditionally thought to be “undruggable”. She hopes to target these floppy regions with newly designed proteins that her AI-guided computer methods hallucinate.

The huntingtin protein has lots of these floppy regions which HD scientists have shown to be important for how the protein knows where to go in the cell and which proteins to hang out with. Kejia is applying her technology to huntingtin to try and design new proteins which target the long string of glutamines found at the start of the disease-causing protein. There is a similar string of glutamines in regular huntingtin protein, but it is a lot shorter. However, the difference is subtle, so finding something selective is tough!

The HD community is lucky to have so many technology experts like Kejia and Tan interested in working on understanding HD and helping us find new ways we might design medicines for the future!

Gill Bates: Toxic Fragment HTT1a

Our next speaker is Gill Bates from University College London. Gill’s group are focussed on a type of huntingtin protein called HTT1a. This is a small fragment of the huntingtin protein which forms toxic clumps in cells.

Gill’s team are looking at how much of the HTT1a form is made in different models of HD. It turns out that the longer the repeat length of the HD mutation, the more HTT1a is made. At the same time, the levels of the full-length form of huntingtin go down.

Next Gill’s team looked to see if there were changes in how much protein was forming toxic clumps. They believe that HTT1a could be the catalyst which kicks off huntingtin protein clumping. To try and figure this out they used a special mouse model of HD which is not able to make HTT1a. These mice have many fewer clumps than regular HD mice, and these clumps form more slowly.

These protein clumps, aka aggregates, are thought to be toxic to cells in many different ways. One of the most studied ways is how clumps in the nuclei of cells, where the genetic material is stored, can impact which genes are switched on or off. Gill and her team looked at how clumps in the nucleus tracked with these genetic changes. The more clumps they saw, the more genetic changes they saw.

HD scientists are still trying to figure out exactly how much each type of huntingtin protein is responsible for causing disease in HD. Gill and colleagues are using genetic tools which target just one type of the huntingtin protein to tease out what is happening.

Looking at aggregate levels and which genes are switched on and off, they found that lowering the amounts of HTT1a and the expanded huntingtin had the biggest effect, however they didn’t see a large effect for lowering other types of huntingtin in the mouse models they used. This matters for the field as we have all sorts of huntingtin lowering therapies in the clinic which each work slightly differently and each lower different forms of huntingtin protein that exist in the cell. We don’t yet know which is going to work out best in people so the more we understand at this detailed molecular level, the better.

Gill is working with the Khvorova lab in the US to design new tools to lower levels of HTT1a. They are developing siRNAs which target huntingtin message molecules and reduce levels of HTT1a protein. More tools for our HD toolbox!

Won-Seok Lee: Influence of Protein Clumps on Somatic Instability

Next up is Won-Seok Lee from the McCarroll lab at Harvard Medical School. Recently, the McCarroll lab published a paper showing that vulnerable cells in HD have somatic expansion – where the CAG number increases a lot in specific cells.

In HD mouse models which have enormous CAG repeats, we see lots of aggregates. In people, only a few cells end up with these huge CAG repeats and we see relatively fewer aggregates. However we don’t know if the cells with the aggregates are the ones with the long CAG numbers.

The McCarroll team wanted to figure this out! They sorted post mortem human brain samples to find the cells with the aggregates. They then figured out that the types of brain cells which have the aggregates are spiny projection neurons – the cells most impacted by HD – which were also the cells that had very long CAG numbers.

Next they looked to see how genes were switched on and off in these cells and saw that these cells had rather wonky genetic signatures, with genes switched on which should have been off and vice versa. This is big news as it links somatic instability with aggregate formation in human tissue samples AND with messed up gene regulation, a hallmark feature of HD.

Next, they tried to figure out which type of huntingtin protein was found in the aggregates and it looked like it was mainly the fragment HTT1a we heard about earlier from Gill. Together, this work is helping us understand how each form of huntingtin is contributing to disease, which is critical for making sure we are targeting the right version with therapeutics.

Spark Therapeutics: Non-Clinical Testing of SPK-10001

The final talk of this session is from Liz Ramsburg from Spark Therapeutics. Spark is a gene therapy company with a big focus on HD. Spark are making gene therapies which lower huntingtin levels. The therapy is packaged into a harmless virus which can then infect cells to deliver the machinery which lowers huntingtin.

The best way that Spark found to deliver their drug was by direct brain injection. Although this sounds like quite a scary approach, the drug generally worked well in animal models they tested when delivered this way. Spark are working to improve their surgery procedure to reduce side effects.

Their drug, SPK-10001, seems to spread well through the brain and levels of huntingtin go down in a dose dependent way i.e. the more drug you give, the more you reduce the levels of huntingtin.
Spark followed the animals for a year after they received the drug and things looked generally fine in terms of side effects, changes to brain structures, etc. NfL levels also seemed to stabilise in a reasonable timeframe. This suggests the drug is pretty well tolerated – good news!
We look forward to learning more about Spark’s progress developing SPK-10001. Liz says she hopes they will be in the clinic soon!

Somatic Instability & Mismatch Repair

Dorothy Erie: Seeing Molecules With An Atomic Record Player

First up this afternoon is Dorothy Erie who studies proteins involved in DNA damage response. Her lab team uses a technology called atomic force microscopy, or AFM, to find out about how proteins stick together. AFM works a bit like a record player, with a needle that drags over the surface, and reveals the topology or nooks and crooks of a sample. AFM works at the molecular level and so instead of the needle helping play the music of a record, it gives us information about whatever is on the surface, in this case, proteins.

As many of you may remember, DNA damage response is a hot topic in HD, as many of the genetic modifiers encode DNA damage repair protein. Understanding how these molecular machines work could help us unpick their role in HD.

Using AFM, Dorothy and her team can see all of the different shapes which these proteins can make. They move around a lot which she likens to dancing the macarena!

Brinda Prasad: Targeting Modifiers

Next up is Brinda Prasad from the CHDI foundation. She will be talking to us about different approaches to therapeutically target a specific DNA repair complex, called MutSBeta. This is a hot drug target in HD being pursued by lots of researchers in academia and different companies.

MutSBeta is actually made up of two different proteins called MSH2 and MSH3. You may remember MSH3, as this is one of the genes which was identified as a genetic modifier of HD. Scientists think if we can switch it off or reduce the levels of MSH3, we might delay onset of HD.

There are lots of different ways that scientists have thought up to target MutSBeta. MutSBeta works with other DNA repair machines, so Brinda and colleagues made special circular blocking molecules which stop it from sticking together with these partners.

Next, Brinda and colleagues looked into switching off the activity of MutSBeta with small molecules. They have a whole suite of different experiments to test these molecules to see how well they are working and develop them to have desirable drug-like properties. This MutSBeta inhibitor program is going well and they are hoping to start testing some of their lead molecules in animal models of HD later on this year.

Another program in this area at CHDI is making chemicals which knock MutSBeta off of DNA. These particular tools stick irreversibly to MutSBeta and stop it from doing its normal job – working directly on the DNA strand to repair damage.

CHDI are making all of the tools and experimental systems available for the research community to help scientists around the world pursue this critical drug target and accelerate progress. That’s what we like to see!

Britt Adamson: Editing The Genetic Code

Next up is Britt Adamson from Princeton University. She is also studying DNA damage response in HD, focussing on mismatch repair proteins. These molecular machines are thought to be responsible for somatic instability and so shutting them off is one way some scientists think we might treat HD.

Her lab uses genome editing tools to study mismatch repair proteins. They deliberately introduce errors into the genome and then figure out which proteins are important for their repair and what types of edits they each prefer. They tested a TON of different edits in cells which are lacking different mismatch repair proteins to try and map who is doing what – very cool and a great resource for the field!

Britt’s team have developed this methodology into a cool new platform to test small molecule inhibitors of MutSBeta. They can rapidly assess how well the inhibitors work as well as how specific they are for MutSBeta over other mismatch repair proteins. Technology developments like this will really help drive drug discovery in this area and ensure drug hunting scientists are only progressing the very best molecules which are on target and selective for MutSBeta.

X. William Yang: Genetic Modifiers Drive CAG Expansion and Disease

Next, we will hear from X. William Yang, from UCLA. William’s team uses mouse models to study HD. Today, we’ll hear about his work on, you’ve guessed it, mismatch repair proteins!

William is reminding us about the impactful large human genetic studies that identified other genes besides huntingtin that can affect when symptoms start to appear. Mismatch repair genes were identified thanks to you, the HD community, signing up for natural history studies!

William and his team are studying these genes in different mouse models of HD. His team are world experts in mouse genetics! While mice are not the same as humans, there are some similarities as to which brain regions are affected in HD in these models compared to humans. This allows them to ask questions about the role of mismatch repair in disease progression in these models.

A key finding of this study is that totally removing MSH3 seems to help restore many of the molecular signatures of HD, in the mouse model they used. Genes which were incorrectly switched on or off in HD mice were returned to regular levels when they got rid of MSH3. This is good news for folks working to develop drugs that target MSH3, as it suggests that many features of HD could be corrected by this type of therapeutic.

Not surprising given its role in DNA repair, removing MSH3 also helped to reduce somatic instability. Other features were also corrected, such as the protein clumps that tend to build up in the mouse brain, as well as some of the behaviours associated with HD mouse models. William reminds us that mouse models are useful tools to study HD but this is a human disease, we must validate findings in people and human-based models too.

Anastasia Khvorova: Two Targets, One Drug

The final talk of the day is from Anastasia Khvorova from the University of Massachusetts. Anastasia’s team are working to develop RNAi-based therapies that target both mismatch repair proteins AND huntingtin protein levels at the same time.

Anastasia’s group has expanded their repertoire of RNAi tools to reduce a whole panel of mismatch repair proteins in a mouse model of HD. This helps us understand which proteins will make the best targets. At this stage of the day, you might have guessed which was most important…. If you guessed MSH3, you would be correct!

Next they looked to see what happened to the levels of different mismatch repair proteins when you knock down MSH3 or other proteins in their panel. This way, they hope to map out which proteins hang out together or rely on each other in the cell.

To look into this further, Anastasia’s group looked at knocking down MSH3, the huntingtin protein itself, or both at the same time, in a mouse model of HD. The mice seemed to have better behavioural signs and symptoms of HD in all cases. The combination treatment seemed to edge out MSH3 or huntingtin knock down treatment alone in terms of reducing levels of the toxic protein clumps and some other molecular readouts.

This work is still ongoing so we look forward to learning more from Anastasia and colleagues when they have more data to share with everyone.

That’s all for Day 1 of the 20th Annual Huntington’s Disease Therapeutics Conference! Stay tuned for Day 2!

We all know that exercise is good for our bodies, but what if working out your brain could slow down Huntington’s disease (HD)? Dr. Estela Càmara and her wonderful team from IDIBELL, a research institute in Spain, have uncovered some exciting news: staying mentally active throughout your life might actually help slow brain shrinkage and symptom progression in people with HD.

Measuring Mental Workouts

HD gradually damages brain cells, leading to problems with the individual’s mood, movement, and mind. But new research suggests that cognitive engagement – keeping your brain busy with activities like reading, puzzles, or learning new skills – could help protect the brain, possibly slowing down progression of symptoms of HD.

So how did Dr. Càmara and her team actually test the impact of mental workouts on HD progression? They began by recruiting people who had tested positive for HD – both individuals displaying motor symptoms, as well as individuals who were not yet displaying any motor symptoms.

All participants completed one questionnaire at the start of this study, which measured how much mental exercise had been done over each person’s lifetime – basically a brain workout scorecard! Examples of mental exercises included how long people were in school for, their jobs, and hobbies that kept their minds buzzing.

Following this, participants completed a number of questionnaires that provided measures of how well their mind functions, as well as questionnaires that assessed their mood. The questionnaires focussing on mind and mood symptoms were followed up on a yearly basis, over a period of 6 years.

Tracking Brain Gains

Once this study was complete, researchers then applied some complicated mathematical models to track how mind and mood symptoms changed over time in people with HD, factoring in their brain workout scorecard. Essentially, they wanted to see if more “brain workouts” meant a slower decline in mind and mood symptoms.

The researchers also used high-tech brain imaging to track changes in the brains of people with HD over time. Think of it like a time-lapse video of the brain.

They wanted to see if people with HD who exercised their brains more had better brain maintenance. In other words, would their brains shrink less over time, compared to those who were not as keen in engaging their brain in the latest novel or crossword puzzle? Each person with HD involved in the study had one image of their brain taken at the beginning of the study and another brain image taken after 18 months.

Mental Reps: Lifelong Learning Builds Brain Strength

From the complicated mathematical models created, scientists concluded that not everyone with HD experiences symptoms at the same rate. However, what made the difference in the rate of decline of symptoms? The authors suggest that it’s a person’s lifetime of cognitive engagement.

The researchers stated that people who regularly challenged their minds throughout their lives, whether it be through education, careers, or hobbies, tended to show slower progression in movement, mind, and mood symptoms of HD. In short, perhaps staying mentally active might not just keep your brain sharp, but it could also help hold some HD symptoms at bay.

However, one question you might be asking is, how does being mentally active relate to slower progression in HD symptoms? Dr. Càmara and her team considered one possible explanation for this slower progression in HD symptoms by looking at the brain images taken in this study. These brain images showed that people with HD who engaged in lifelong mental workouts had stronger brain resilience. This means that their brain structures stayed healthier for longer.

Specifically, key areas of the brain involved in mind (such as decision-making and self-control), mood (such as emotional regulation), and movement symptoms were better preserved. So perhaps this stronger brain resilience could be one reason behind why HD symptoms progress more slowly in those who have had their regular sessions in the brain gym over their lifetime.

Flex Those Brain Muscles

The good news is that you don’t need a PhD to give your brain a workout! While specific activities for stretching your mental muscles weren’t covered in this recent publication, there’s lots of evidence to support various actionable items that can help give you a good brain workout. Here are some fun ways you can stay mentally active:

• Puzzles & Games: Crosswords, Sudoku, and memory games can keep your brain on its toes.
• Read & Learn: Books, audiobooks, or even podcasts can spark new ideas and strengthen brain connections.
• Language: Learning a new language is a strenuous mental workout that deeply challenges various areas of your brain.
• Music & Creativity: Playing an instrument or learning a new craft can challenge different parts of the brain.
• Socializing: Chatting with friends, debating topics, or even storytelling can help to keep thinking skills sharp.

A Mental Workout Against HD

HD is a tough opponent, but science is showing us that mental activity may help slow it down. While it’s not a cure, keeping your brain busy is a simple, fun way to fight back against Huntington’s. So, grab a book, solve a puzzle, or try something new – your brain will thank you.

A new study led by researchers from the University of California Irvine gives us new clues as to how genetic message molecules are edited differently in the context of Huntington’s disease (HD). Let’s get into what the scientists found and why this matters for our understanding of HD.

The cellular editor

When watching our favorite movies, we don’t typically consider the extraordinary amount of editing required to make them flow seamlessly from scene to scene. Behind this movie magic are editors who work tirelessly to enhance the drama of key plot twists with clever and precise cuts, removing unnecessary scenes and bloopers, and eventually stitching everything together to create the polished films we love.

Cells use a similar editing process when creating proteins, the molecular machines that perform nearly all the activities inside cells. Proteins are like polished feature-length films in theater and, just as movies originate from a collection of unedited scenes, proteins are also made from an unedited version called mRNA.

mRNA is a long string-like molecule with multiple “scenes” containing the genetic instructions needed to make protein. Through an important process called splicing, cells remove segments of mRNA called introns (bloopers) and keep segments called exons (key plot twists). If everything runs smoothly, the initial unedited mRNA, containing a mix of introns and exons, will have its introns removed leaving it with only exons when it is used to make proteins.

However, this editing process malfunctions in people with HD, leading to serious problems in how some of the protein machines work inside brain cells.

Cells with bloopers and missing scenes

Scientists have long suspected that mRNA splicing is disrupted in the brains of people with HD. Previous research has found introns mistakenly included in the final mRNA molecule and exons mysteriously missing. This would be like publishing movies without removing bloopers and missing critical plot twists – not something cinema-goers would be happy with!

Recent experiments suggest that the protein encoded by the gene that causes HD, called Huntingtin (HTT), may play a key role in this confusion. HTT is an mRNA-binding protein and is known to interact with other proteins that also bind mRNA. This raises an interesting question: if splicing is disrupted in HD, HTT interacts with mRNA, and HTT interacts with proteins involved in splicing, could mutant HTT be interfering with the cell’s mRNA editing process?

Blockbuster bombs in the cell

Intrigued by this mystery, Dr. Leslie Thompson and her team at the University of California Irvine investigated the underlying cause of splicing errors. Using mouse models of HD and post-mortem human brains, they first confirmed that splicing is disrupted in the HD brain, discovering various types of mRNA with undeleted introns (bloopers) and missing exons (key scenes). These errors were most common in the medium spiny neurons, the type of brain cell that is most vulnerable in HD. In addition, the mRNA message molecules that were found to contain splicing errors were particularly important for activities like neural communication and brain development.

Splicing errors are harmful because a cell’s protein machines made from improperly spliced mRNA either function abnormally or fail to be produced altogether. This would be like a movie so poorly edited that the publisher decides to pull it before hitting theaters.

These findings are exciting for HD researchers because they may explain why some proteins don’t work very well or are less abundant in HD cells, despite having no mutation or known interaction with HTT. Although the consequences of splicing errors are complex and difficult to predict, they are undoubtedly harmful to overall brain function.

TDP43: A distracted editor

Leslie and her team scrutinized the proteins interacting with HTT in search of possible causes of the splicing errors. They focused on proteins that, like HTT, also interact with mRNA – like partners in crime.

One protein, TDP43, stood out because it not only interacts with HTT and mRNA but is also known as a kind of splicing editor-in-chief. TDP43 is an extensively studied protein because its mutation causes a different neurodegenerative disease, Amyotrophic Lateral Sclerosis (ALS), so researchers already have a great profile on it. Adding to their suspicion, the types of mRNA that TDP43 is known to edit closely overlap with the mRNA containing splicing errors in HD.

Beginning their investigation of TDP43, Leslie and her team first tested if TDP43 binds to the same mRNA that is spliced incorrectly in HD. Sure enough, they found that TDP43’s favorite mRNA largely overlapped with the abnormally spliced mRNA in HD. When researchers compared the splicing changes of cells missing TDP43 to cells containing mutant HTT, they observed remarkable similarities. This suggests that TDP43 dysfunction might be the root cause of splicing errors in HD.

How HTT spoils the show

The team hypothesized that HTT’s interaction with TDP43 could be “stealing” it from the studio, and preventing it from splicing mRNA. To test this, they first confirmed that HTT interacts with TDP43 in mouse brains. Next, they examined brain cells from people with HD to see if TDP43 was in its normal location, the nucleus, where splicing occurs. Like an absent movie editor, TDP43 was mostly located outside of the nucleus, a clear indication that something was wrong.

Scientists have long recognized changes in TDP43 location from the nucleus to the cytoplasm (outside the nucleus) as a hallmark of ALS, and this change in location is associated with errors in splicing. What’s worse, the small amount of TDP43 still in the nucleus appeared inactive because it was locked up in big protein clumps with HTT, like an editor buried by movie reels!

Another red flag the scientists noticed was the absence of special chemical markings on mRNA, called m6A, that guide TDP43 to splice sites, like sticky notes reminding the editor to delete certain scenes. These chemical markings on mRNA were significantly reduced in HD brains, particularly on mRNA prone to splicing errors. Without these marks, TDP43 is unable to identify the “bloopers” it needs to remove and likely contributes to TDP43’s dysfunction.

At this point, the researcher’s working hypothesis was that mutant HTT abnormally interacts with TDP43, keeping it out of the nucleus or trapping it in large clumps, distracting it from its splicing duties. On top of this, the sticky notes (m6A marks) that guide TDP43 to the bloopers (introns) were mostly missing in HD brains. Together, these issues prevent mRNA from being properly edited, resulting in broken or missing protein machines. Over time, these problems lead to sick brain cells that can’t communicate properly.

Putting the editor back to work

Although the current study does not attempt to correct or reverse these splicing errors, its findings will help guide future therapeutics. The involvement of TDP43 is particularly interesting because TDP43 is already extensively studied in ALS, and hundreds of TDP43-targeting therapies are currently in development. This does not necessarily mean treatments designed for TDP43 will work for HD, but they may serve as promising starting points for new therapeutic strategies or to help us better understand what TDP43 is doing in HD.

Future research is critical to understanding how mutant HTT disrupts TDP43 activity, and whether restoring TDP43 activity can correct the splicing errors observed in HD. Like editing a movie, fixing these molecular errors could turn a blockbuster disaster into a beloved masterpiece we cherish for years to come.

A new paper led by researchers at the Massachusetts General Hospital and Harvard Medical School used CRISPR to work out which genes can influence how the genetic C-A-G repeat that causes Huntington’s disease (HD) can change over time. This exciting study helps us to better understand how HD works and uncovers some potential targets for therapies that could slow or halt the disease.

Genetic Stumbles Can Increase C-A-G Repeats

HD is a genetic brain disorder and everyone who has HD has an expansion of the C-A-G DNA letters in their HD gene, also called huntingtin or HTT. Over time, these C-A-G repeats can become even longer in some types of brain cells. This process is called somatic instability or more specifically somatic expansion. But somatic expansion doesn’t occur in all cells. This phenomenon appears to occur more so in medium spiny neurons, the type of cells that are most affected in HD.

The topic of somatic instability has been trending in the HD field, as it is suggested to be a key driver of disease that may accelerate the age at which symptoms first appear. This is supported by large genetic studies in people with HD, which suggest that genes responsible for proofreading the genetic code can affect somatic instability.

Billions of DNA Pieces: The Puzzle of Life

Every cell in the body carries a complete set of DNA instructions, which act like a blueprint for making everything the body needs to grow, function, and stay alive. You can think of DNA like a twisted ladder, and its two strands are the sides of the ladder. The rungs of the ladder are made up of building blocks, known as A (adenine), T (thymine), C (cytosine), and G (guanine). These act like puzzle pieces that pair up in a very specific way: A always pairs with T, and C always pairs with G.

The DNA in each of our cells contains billions of these letters, so as you can imagine, sometimes there are mistakes or mismatches in the DNA puzzle leading to two pieces being paired up that don’t fit together properly. Luckily our cells have repair systems that work like mini-puzzle masters, scanning for these mistakes, removing the wrong piece, and replacing it with the right one so the puzzle or DNA fits together perfectly again.

When it comes to long C-A-G repeats in the huntingtin gene, sometimes, the two DNA strands can shift or “slip”. DNA slips in C-A-G repeat regions are like buttoning your shirt but skipping a button—causing a bulge that disrupts the whole pattern. This happens because the C-A-G sections of DNA are like identical puzzle pieces that can stick together in the wrong way.

If this happens, a loop of extra CAGs can form in one strand DNA. Since the DNA repair systems are always checking for mistakes, when they notice the loop of extra CAGs, they try fix it. But instead of removing the extra CAGs, it sometimes “corrects” the strand by adding more repeats to make everything match. This leads to expansions of the CAG repeat in huntingtin.

Measure Twice, Cut Once: Using CRISPR To Uncover Genes Behind Genetic Stumbles

In this paper, the researchers used CRISPR to turn-off specific genes in a mouse model of HD. CRISPR is a powerful tool that acts like a tiny molecular Swiss Army knife in the cell to cut or edit any DNA as long as there is a “homing” signal (or PAM site) nearby. Luckily these homing signals are found nearly everywhere in the genome, so researchers are finding cool ways to use CRISPR to edit literally any gene in the cell!

This tool is being used to correct typos in genes, including the huntingtin gene in HD. It can also be used to turn-off certain genes, which reduces the amount of protein they make.

The researchers focused on genes involved in cell’s DNA repair systems, since prior studies have suggested that some of these genes play an important role in controlling the stability of C-A-G repeats, either by making them longer or shorter.

They used CRISPR to turn-off more than 50 of these genes in HD mice and then measured the effect on C-A-G repeat changes in the striatum, the part of the brain most affected in HD, as well as in the liver.

Expanding and Contracting: How DNA Repair Genes Play CAG Repeats Like an Accordion

The study confirmed that several genes in the DNA mismatch repair pathway, such as MSH2, MSH3, and MLH3, make proteins that can enhance expansion of the C-A-G repeat. When these genes were turned off, less of these proteins were made and the expansion slowed significantly. This emphasizes the potential of targeting these proteins as drug targets for HD.

On the other hand, switching off certain genes, like FAN1 and PMS2, made C-A-G repeats expand faster. This suggests that boosting the production of these proteins could help slow down C-A-G expansion.

Interestingly, turning off DNA repair genes had different effects depending on the tissue. For example, some genes caused more C-A-G repeat expansion in the liver than in the striatum. This shows why it’s important to study these changes in the tissues most affected by the disease.

This study shows how powerful CRISPR can be for testing genes that affect C-A-G repeat instability directly in living animals. It allows scientists to study dozens of genes at once, something that wasn’t possible before.

‘Harness’-ing C-A-G Expansions

The findings help us better understand what drives HD and point to new potential drug targets that could slow C-A-G expansion and delay symptoms. In fact, there are lots of folks doing exactly that right now!

Rgenta Therapeutics and LoQus23 Therapeutics are two companies developing pills that aim to turn off production of proteins that make the C-A-G repeat longer, which could help slow down somatic expansion in the brain.

Another company, Latus Bio, is planning to use harmless viruses to deliver DNA-like molecules, known as microRNA, that can lower levels of a protein that can increase somatic expansion.

Harness Therapeutics is working on developing specialized DNA molecules, known as antisense oligonucleotides or ASOs, that are designed to boost production of FAN1, a protein that can actually make the C-A-G repeat shorter.

These treatment approaches are still in the research stages so be sure to check HDBuzz for updates as these programs move along.