2026 Conference | CHDI Foundation

CHDI’s 21st Annual HD Therapeutics Conference took place February 23 – 26, 2026 in Palm Springs, California. This unique conference series focuses on translational drug discovery and development for Huntington’s disease and draws participants from the biotech and pharmaceutical sectors as well as academia. The conference is intended as a forum where all participants can share ideas, learn about new disciplines, network with colleagues, and build new collaborative partnerships. We are indebted to all of the conference speakers, and especially grateful to those who are able to make their presentations available here for a wider audience.

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- - Featured Speaker
  - Pathogenesis studies of neurodegenerative diseases: The rare informs the common Huda Y Zoghbi, MD, Howard Hughes Medical Institute

AMT-130 slows Huntington’s disease progression at 3 years: Propensity score weighting mitigates potential bias from striatal volume absence in Enroll-HD

David H Margolin, MD, PhD, uniQure

BACKGROUND: AMT-130 is an investigational Huntington’s disease (HD) gene therapy that generates
an exon-1 HTT-targeting miRNA, thereby inhibiting production of the mutant huntingtin protein (mHTT) protein, including the pathogenic protein fragment derived from HTT1a. A 3-year interim analysis compared outcomes from clinical studies CT-AMT-130-01/02 to a matched natural history cohort from Enroll-HD to assess the efficacy of AMT-130 as a potential disease-modifying treatment. AMT-130 met primary (change in the Composite Unified Huntington’s Disease Rating Scale [cUHDRS]) and key secondary endpoints (Total Functional Capacity [TFC]). AMT-130 demonstrated statistically and clinically significant slowing of disease
progression by 75% based on cUHDRS (P=0.003) at 3 years compared with progression in matched controls from the Enroll-HD natural history study. Striatal volume, which had specified minima in CT-AMT-130-01/02, has previously been shown to impact the rate of clinical progression.

OBJECTIVE: To demonstrate the robustness of the 3-year analysis interpretation with respect to selected baseline characteristics and study design elements.

METHODS: Clinical eligibility criteria were applied to both AMT-130 and Enroll-HD datasets, and AMT-130 enrollees additionally met minimum striatal volume criteria (2.5 cm3 putamen, 2.0 cm3 caudate, each side). Propensity score (PS) matching was used to balance baseline characteristics across cohorts. Additional analyses were performed on data from TRACK-HD/Track-On HD and PREDICT-HD (TTP-HD) to examine potential bias linked to the striatal volume criteria in the interpretation of 3-year outcomes. Separately, an additional AMT-130 cohort arm was initiated in which enrollment criteria included at least one striatal volume below the prior minima.

RESULTS: Analyses of TTP-HD show that volumetric criteria had no impact on change in cUHDRS or TFC scores from baseline to year 3 after PS weighting of baseline covariates was applied. The lower striatal volume cohort has been fully recruited; their baseline characteristics will be reported.

CONCLUSION: AMT-130 demonstrated statistically and clinically significant slowing of disease progression. These results demonstrate that the use of MRI volumetrics as eligibility criteria do not introduce bias in the
study population. Study of participants with lower striatal volumes is ongoing.

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Liquid-liquid phase separation in cell physiology and disease

Cliff Brangwynne, PhD, Princeton University & Howard Hughes Medical Institute

Living cells are often viewed as functioning through a clockwork-like set of interactions among their biomolecular building blocks, like machines on a factory floor. But the processes taking place within cells are vastly more wet and dynamic than many textbooks would have us believe. Over the last 15 years, research combining insights from materials physics and cell biology has ushered in a new paradigm for understanding how this chaotic intracellular environment is brought to order, through the collective condensation of biomolecules into droplets of living information. In this talk, I will present an overview of these principles and ongoing work in this field, with a particular emphasis on the interplay between liquid-like biomolecular condensates and the more solid-like protein aggregates found in Huntington’s and other neurodegenerative diseases. I will also discuss this interplay in the context of our lab’s work on the multiphase nucleolus and the ribosome nanomachine, which is responsible for cytoplasmic translation, and thus a central player in protein folding and proteostasis. Our lab has recently developed a set of tools to probe and engineer the complex process of ribosome biogenesis, including time-dependent changes to ribosome translational output. These studies are yielding new insights into how assembled ribosomes function in space and time and are dysregulated in disease.

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Condensing on huntingtin: RNA, phase separation, and the effect of polyQ expansion

Rachel J Harding, MBiochem, DPhil, University of Toronto

The molecular mechanisms linking polyglutamine (polyQ) expansion to cellular dysfunction remain incompletely understood. Recent work from our group reveals that full-length huntingtin (HTT) protein is not merely a structural scaffold but directly engages RNA and participates in biomolecular condensates. Using a combination of biochemical, biophysical, and cellular approaches, we showed that both wild-type and expanded HTT interact with RNA, with a pronounced affinity for G-rich sequences, including the long noncoding RNA NEAT1. In this interaction, HTT localises to paraspeckle structures, membraneless nuclear bodies formed via liquid-liquid phase separation (LLPS). This HTT-RNA interaction suggests a functional role for HTT in RNA-mediated nuclear organization and stress response pathways, expanding the functional repertoire of HTT beyond traditional protein-protein interactions observed in HD models to date.
Building on these insights, we have investigated the LLPS behaviour of full-length HTT in vitro. We found that under crowding conditions mimicking intracellular environments, highly pure recombinant full-length HTT undergoes LLPS to form dynamic droplets. Critically, the morphology of phase separated structures is altered with expanding polyQ tract length. These phenomena are accompanied by changes in droplet dynamics and fusion behaviour, suggesting a direct link between polyQ length and condensate material state. Wildtype HTT LLPS structures are consistently liquid-like and undergo more rapid exchange, whereas expanded HTT LLPS structures form more gel- or solid-like states with reduced exchanges between phases. Our data indicate that expanded polyQ domains alter the dynamics of condensate assembly, potentially biasing droplets toward less reversible and more pathological assemblies.
Together, these findings position HTT as a multivalent RNA-binding scaffold whose phase behaviour is tuned by polyQ expansion. We propose that aberrant LLPS of HTT, coupled with altered RNA interactions, may contribute to HD pathogenesis by disrupting normal RNA metabolism, nuclear body dynamics, and cellular stress responses. Elucidating these mechanisms opens new avenues for therapeutic intervention aimed at modulating condensate dynamics in neurodegeneration.

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The role of protein tags and heterologous condensates in HTT1a phase separation 1

Ralf Langen, PhD, University of Southern California

Huntingtin aggregation is a hallmark of Huntington’s disease (HD). An important N-terminal fragment of huntingtin (HTT1a) is formed by aberrant splicing of HTT, resulting in the expression of only the first exon. Many cellular studies on HTT1a have visualized the protein using fluorescent protein tags, such as GFP or RFP. This includes studies showing that HTT1a can undergo liquid–liquid phase separation (LLPS), a process that has recently risen to prominence as it underlies the formation of membrane less organelles and governs the dynamic compartmentalization of many cellular functions.
Using recombinant proteins, we were able to confirm that tagged HTT1a undergoes LLPS. Moreover, we found that LLPS potently enhances the transition to the solid, fibrillar state. However, using biochemical, biophysical, and cellular studies, we found that the untagged protein lacks the ability to undergo LLPS. Unlike the aggregation of the tagged protein, the untagged protein is not sensitive to hexanediol, a molecule that can disrupt LLPS. In addition to affecting LLPS, fluorescent protein tags also strongly alter HTT1a aggregate size in cells and the morphology of recombinant fibrils. Thus, we conclude that fluorescent protein tagging not only promotes LLPS but also fundamentally alters the aggregation mechanism and fibril formation of HTT1a.
To determine whether untagged HTT1a might be able to localize to condensates by binding to well-known condensate formers, we studied the interaction of HTT1a with TDP-43, a known HTT1a binding partner. While soluble, monomeric HTT1a is excluded from TDP-43 coacervates, fibrillar HTT1a efficiently co-mixes with these droplets. Interestingly, this interaction potently inhibits further HTT1a aggregation but promotes the fibril formation of TDP-43. These results suggest that while HTT1a may not undergo LLPS on its own, it can still be recruited to cellular condensates, potentially even through heterotypic interactions mediated by its solid, fibrillar state.

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Beyond CAGs: how the flanking CCN-rich sequence shapes HTT toxicity from RNA processing to neuronal dysfunction

Elena Cattaneo, PhD, University of Milano & National Institute of Molecular Genomics

Increasing evidence indicates that CAG-repeat length alone within exon1 of the HTT gene is insufficient to account for the variability and severity of Huntington’s disease (HD) phenotypes. In parallel, the traditionally protein-centric view of pathogenesis has expanded toward a nucleic acid-centered model, in which DNA-RNA sequence context, structure, and metabolism emerge as critical determinants of disease mechanisms. Here, I will present unpublished data addressing how the proline-encoding CCN-rich domain (proline rich domain, PRD) flanking the CAG repeats acts as a key cis-modifier of HTT biology and toxicity, shaping pathogenic outcomes across both RNA and protein layers.
Using the “HuntEx1” cell platform—our modular recombination-based mouse embryonic stem cell system enabling precise and rapid manipulation of HTT exon1—we conducted comparative structure-function analyses of HTT variants. These studies show that mutant human HTT exon1 is intrinsically more pathogenic than the murine counterpart, and that this species-specific toxicity maps to the PRD. Replacing the human PRD with the murine sequence in human HTT exon1 is sufficient to rescue aberrant neuronal phenotypes and activity, as well as pathological proteomic signatures. Bioinformatic analyses of these datasets converge on cytoskeletal regulation as a dominant PRD-sensitive pathway, implicating a transcriptional co-activator in the control of dendritic outgrowth, with consequences for downstream synaptic functions.
Proteomic data further suggest that the PRD modulates RNA splicing and processing. Human-specific PRD nucleotide sequences reshape exon1 RNA structure, altering accessibility to splicing regulators and potentially favoring activation of cryptic polyadenylation sites that generate the toxic HTT1a transcript. We identify a PRD-dependent splicing factor regulating this process and show that modulating HTT1a production impacts neuronal morphology.
Together, these findings position the PRD as a multifunctional cis-regulatory hub contributing to HTT toxicity through distinct RNA- and protein-level mechanisms. By linking RNA structure and processing to cytoskeleton-dependent neuronal dysfunction, this work highlights the importance of sequence context beyond the CAG repeat itself. In parallel, our complementary human embryonic stem cell-based HTT exon1 platform, “CAGinSTEM”, encompassing multiple CAG lengths and haplotypes, provides an additional human system to investigate HTT DNA-RNA biology and toxicity (Zobel et al., 2025).

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Epitranscriptomic control of HTT RNA metabolism: m6A methylation as a driver of HTT1a pathogenesis

Veronica Brito, PhD, University of Barcelona

Transcriptional dysregulation is a hallmark of Huntington’s disease (HD), with extensive alterations in RNA processing and abundance documented across numerous HD models. However, prevailing molecular models primarily emphasize steady-state transcript levels, often overlooking the chemical modifications that dictate RNA fate. Recent evidence from our group and others suggests that the epitranscriptome—the collective landscape of RNA chemical modifications—represents a critical regulatory layer that integrates transcriptional and post-transcriptional control to drive disease-relevant RNA dysregulation.
Our transcriptomewide analysis of N6methyladenosine (m⁶A), the most abundant internal RNA modification in the brain, revealed reproducible alterations in m⁶A deposition across the HD transcriptome in a knockin HD mouse model. Notably, these changes were independent of transcript abundance, indicating that epitranscriptional dysregulation captures regulatory information not reflected in steady-state RNA levels. Among these altered m⁶A patterns, we discovered that Htt transcripts emerged as prominent targets, displaying enriched m⁶A deposition within intron 1—an intronic region associated with the aberrant RNA processing that generates Htt1a isoform. We show that this methylation is present in polyadenylated transcripts generated by incomplete splicing and is influenced by CAG-repeat length.
Given that m6A influences several aspects of Htt RNA metabolism, we explored its functional impact on Htt1a expression in both in vitro and in vivo HD models. We demonstrate that m6A deposition regulates the expression of the Htt1a transcript, potentially influencing the production of the toxic Htt1a fragment and offering new insights into the RNA-based mechanisms underlying aberrant Htt processing.
In this talk, I will present the experimental strategies used to identify and validate m⁶A methylation of Htt RNA, as well as genetic and pharmacological approaches to modulate components of the m⁶A machinery and assess their impact on HTT1a expression. Our work underscores the importance of RNA modifications in HD pathogenesis, particularly the mechanisms governing mutant HTT RNA metabolism, and highlights potential gene therapy strategies aimed at targeting the mutant RNA allele or modulating the splicing process that generates HTT1a.

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Mapping HTT1a, aggregation, repeat dynamics and therapeutic interventions targeting mutant HTT DNA and RNA in a human iPSC-derived medium spiny neuron model

Sarah Tabrizi, MD, PhD, FMedSci, FRS, University College London

Huntington’s disease (HD) is a neurodegenerative disease caused by an expanded trinucleotide CAG repeat in exon 1 of the huntingtin gene (HTT). Expansion of the HTT CAG repeat tract in somatic tissues occurs throughout the life of HD patients in post-mitotic neurons and correlates with disease progression and earlier age at onset. A causal role for somatic expansion in HD pathogenesis is supported by genome wide association studies that identified variants in DNA damage genes that bi-directionally alter age at onset. Slowing the rate of somatic instability is therefore an attractive therapeutic avenue. However, key questions remain regarding the mechanism of repeat expansion in human post mitotic neurons and the relationship between somatic instability, cell-type vulnerability, cellular phenotypes and toxic HTT gene products associated with an expanding CAG tract.
The mis-spliced HTT exon 1 transcript variant (HTT1a) has been suggested to be a uniquely toxic HTT gene product, generated in a CAG-dependent manner that seeds HTT1a protein aggregates. As HTT1a production may be the mechanism through which somatic expansion drives pathology, HTT lowering therapies may be less effective if they do not lower levels of toxic HTT1a, or other proposed mechanisms of pathogenesis. Therefore, there is a need to understand the mechanism of expansion to address both HTT toxicity and somatic instability.
Using CRISPR methods, we have generated an isogenic series of iPSc ranging from 20 CAG to 200 CAG repeats. Using iPSc derived human striatal enriched post mitotic neuronal cultures, we have characterized the relationship between CAG-repeat length, HTT1a production, nuclear mHTT aggregation, and how the dynamics of repeat expansion rates alters with increasing CAG-repeat size.
In collaboration with Takeda, we also target key stages of this pathogenic process in human neurons—namely, AAV9-delivered ZFPs targeting the HTT CAG repeat DNA, an allele-selective mHTT-targeting ASO, and an MSH3-targeting ASO—and characterize their impact on CAG-repeat instability and downstream cellular pathologies in human medium spiny neuron (MSN) enriched cultures.

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What goes up… Repeat contractions in HD and other repeat expansion diseases

Karen Usdin, PhD, National Institutes of Health

While expansions have been intensively studied in the context of Huntington’s disease and other repeat expansion diseases, relatively little is known about contractions, which like expansions occur both in germline and somatic cells. Two types of contractions can be seen in different cell types. The first of these involve “progressive” contractions, small decreases in the modal allele size that continue over time. The clearest example of such contractions can be seen in the pituitary where most of the alleles in the population lose repeats over time, in what appears to be a mirror-image of the more familiar somatic expansions. The second contraction process involves larger, more variable decreases in repeat number that we refer to as “stochastic contractions”. Harnessing these contraction processes may represent an alternative to reducing expansions, perhaps most usefully in cases where the repeat number is already in the pathological range. A better understanding of the underlying mechanism responsible for such contractions may help us assess whether this approach is feasible and what some of the relevant targets may be.

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Mechanism of trinucleotide repeat expansion by MutSβ-MutLγ and contraction by FAN1

Petr Cejka, PhD, Institute for Research in Biomedicine

Triplet repeat expansions underlie numerous human pathologies, including Huntington’s disease. The expansions causing these disorders often occur in somatic non-dividing tissues such as the brain. Despite the identification of numerous genetic modifiers that promote or prevent expansions, mechanistic insights are limited. We used purified human proteins and reconstituted reactions in vitro to understand how DNA expansion might occur.
We show that the MutLg(MLH1-MLH3) nuclease stimulated by MutSb(MSH2-MSH3) nicks a DNA strand opposite an extrahelical loop on the 5’ side and exhibits a moderate sequence preference. PCNA restricts the MutLgincision sites to the vicinity of the loop. The MutLg-dependent nicks serve as entry points for displacement DNA synthesis by RPA-RFC-PCNA and Pold. Pold uses the looped DNA strand as a template, leading to repeat expansion. The minimal enzymatic system able to support DNA expansion includes MutLg, MutSb, RPA-RFC-PCNA and Pold.
We also show that the FAN1 nuclease, a known protective factor, preferentially nicks instead the looped DNA strand. RFC and PCNA stimulate and direct the endonucleolytic incision by FAN1 to the 3’ end of the extrahelical loop and restrict FAN1’s exonuclease activity. The RFC and PCNA-driven loop incision by FAN1 does not require a pre-existing strand discontinuity. Following FAN1-RFC-PCNA, Pold’s exonuclease activity in conjunction with RFC-PCNA removes the loop. Pold then resynthesizes DNA, resulting in repeat shortening. The minimal enzymatic system able to support DNA contractions includes FAN1, RPA-RFC-PCNA and Pold.
Additionally, FAN1, through its specific interaction with MutLg, prevents its activation by MutSb. Our data demonstrate how FAN1 prevents the pathological DNA incisions by MutLg-MutSbthrough a combination of structural and catalytic functions. Our reconstituted DNA expansion and contraction reactions provide possible mechanisms underlying triplet repeat instability, explain the protective function of FAN1, and align closely with Huntington’s disease models and genome-wide association studies.

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Real-time imaging of mismatch repair with trinucleotide repeat intermediates

Richard Fishel, PhD, Ohio State University

Expansion of short tandem repeats (STR) cause over 70 human diseases including Huntington’s disease. The mechanism of expansion is largely unknown, although the trinucleotide STR expansion that causes Huntington’s disease is genetically eliminated by mutations of key mismatch repair (MMR) components. The suppression of Huntington’s STR expansions is exactly opposite to similar MMR defects that drive cancer, where STR instability is enhanced (microsatellite instability or MSI). How MMR leads to Huntington’s STR expansion but suppresses MSI is a significant puzzle. Nearly three decades ago our group proposed the Molecular Switch-Sliding Clamp (MSSC) model for MMR. We ultimately developed single molecule resolution methods, including total internal reflection fluorescence (smTIRF) microscopy, to visualize the complete E.coli MSSC mechanics. These studies revealed the cascade formation and properties of the MutS and MutL sliding clamps, and interactions with MutH and UvrD that established exonuclease-independent mismatch strand release as the most likely E.coli MMR mechanism. Similar single molecule imaging analysis confirmed fundamentally identical biophysical properties for the core MMR cancer-associated MutS homolog (MSH) and MutL homolog (MLH/PMS) heterodimers MSH2-MSH6 (MutSα) and MLH1-PMS2 (MutLα). In recent years our group has established four-color smTIRF to examine the functions and collaborations between increasingly complex combinations of MMR components that include MSH2-MSH3 (MutSb), MLH1-PMS1 (MutLb), MLH1- MLH3 (MutLg), PCNA, EXOI, FEN1, and RPA with an array of mismatches and STR intermediates. Crucially, no static complexes were ever observed anywhere on these DNAs. However, significant biophysical differences were noted for the MutSα and MutSbsliding clamps as well as distinctive mechanics and interaction(s) with MutLα, MutLb, and MutLg. Including FAN1 clearly eliminated a widely considered model for its role in STR expansion. The dynamic properties of the MMR complexes with various STR intermediates, along with other single molecule resolution data, support a working model for STR expansion that will be discussed.

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Upregulation of FAN1 with ASOs as a potential therapeutic strategy for triplet repeat disorders

Andy Billinton, PhD, Harness Therapeutics

It is widely accepted that somatic expansion can occur in some triplet repeat disorders, including Huntington’s disease (HD). Efforts to create huntingtin (HTT) lowering therapies are being rapidly followed with potential somatic expansion slowing therapies, including molecules that modulate mismatch repair proteins MSH3, PMS1 and the interstrand crosslink repair protein, FAN1. We have initially focussed our MISBA (MicroRNA Steric Blocking Antisense Oligonucleotide) platform on upregulation of FAN1 as a protein with nuclease activity that can delay onset of HD. We and others identified that a SNP in the 3’-UTR of FAN1 sits in a miR-124 binding site that increases FAN1 mRNA levels and delays onset of HD. We are exploring this and other miR binding sites that can increase the level of FAN1 protein and hence slow somatic expansion of the CAG-repeat tract in HTT. This has involved the creation of FAN1-HiBiT cell lines, identification of potential miR binding sites in the 3’UTR of FAN1 and the establishment of human iPS-derived neuronal and organoid assays, and nanopore-based CAG-repeat sizing as systems to characterise ASOs that modulate FAN1 expression and potentially slow CAG-repeat expansion. We report on the use of these assays to show that MISBA can increase FAN1 mRNA and protein in cell lines. The nanopore-based assay can be used to assess CAG-repeat expansion in human iPS, iPS-derived neurons and neuron-containing organoids. We demonstrate that MISBA can upregulate FAN1 and reduce the rate of CAG-repeat expansion in iPS-derived neurons. We are further developing ASO technology that allows for simultaneous upregulation and knockdown of different targets relevant to somatic expansion and HD.

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Computational modeling and preclinical evidence supporting LTS-201, an MSH3-lowering therapy for Huntington’s disease

Jang-Ho Cha, MD, PhD, Latus Bio

Huntington’s disease (HD) is caused by an expanded CAG repeat in the huntingtin (HTT) gene, with genetic modifier studies identifying somatic instability (SI) as a key determinant of disease onset and progression. In this presentation we will outline the rationale for targeting the DNA mismatch repair protein MSH3 to suppress somatic instability in striatal medium spiny neurons, the cell type most vulnerable in HD. While SI-directed therapies represent a promising disease-modifying strategy, their potential clinical benefit— particularly the optimal timing of intervention and patient populations most likely to benefit—remains uncertain.
To help address this gap, we will present a computational modeling framework that integrates HD patient natural history data to simulate somatic instability within medium spiny neurons and predict the impact of therapeutic intervention across inherited CAG lengths and ages at treatment. Using this approach, we model how varying degrees of regional and cellular target engagement translate into effects on neuronal survival, clinical progression, and functional outcomes. Modeling results suggest that substantial reductions in somatic instability could translate into marked slowing of clinical decline, with predicted improvements in cUHDRS change from baseline ranging from ~50% to >120% and delays in motor symptom onset by several years.
We will also describe supporting in vivo preclinical data from an AAV-based approach to lower MSH3, using an artificial microRNA (miMSH3) delivered with the MSN-targeting AAV-DB-3 capsid. In non-human primates, AAV-DB-3.miMSH3 (LTS-201) achieved 48–94% reduction of MSH3 mRNA in medium spiny neurons, while treatment in HdhQ111 mice resulted in up to a 46% reduction in somatic CAG-repeat instability. Together, these experimental findings and modeling predictions support the translational potential of a SI-targeted gene therapy as a disease-modifying strategy for HD.

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Targeting repeat-expansion at its source: Discovery of RGT-0474060, a PMS1 RNA splice modulator for Huntington’s disease and beyond

Nandini C Patel, MS, Rgenta Therapeutics

Somatic CAG-repeat expansion in the HTT gene drives the progression of Huntington’s disease (HD). While PMS1 is widely recognized as a critical protein for this expansion, PMS1 remains an elusive drug target for traditional small-molecule inhibitors. To overcome this “undruggable” nature, we utilized Rgenta Therapeutics’ RNA-targeting discovery platform to identify a once-daily oral small molecule that knocks down PMS1 by modulating its pre-mRNA splicing.
Our drug discovery campaign integrated high-throughput splice-modulation assays with a proprietary RNA-focused screening deck. Through iterative structure-activity relationship (SAR) cycles, we optimized scaffolds for potency, selectivity, physicochemical properties, and CNS penetrance. This resulted in a series of orally bioavailable modulators that robustly reduce PMS1 RNA and protein levels, leading to dose-dependent suppression of somatic CAG-repeat expansion in HD models.
From this series, RGT-0474060 was selected as a development candidate due to its superior selectivity, safety, and pharmacokinetics. In NHP models, RGT-0474060 achieved sustained PMS1 knockdown in brain and peripheral tissues at well-tolerated doses. Currently in IND-enabling studies, RGT-0474060 represents a promising therapeutic approach that could potentially address the root cause of HD and other repeat expansion disorders. This presentation will detail Rgenta’s workflow of drug discovery, key optimization inflection points, and the emerging profile of this novel drug candidate.

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Epigenetic mechanisms governing cell type specific somatic expansion and toxicity in Huntington’s disease

Nathaniel Heintz, PhD, The Rockefeller University

Huntington’s disease (HD) is characterized by neuronal dysfunction and degeneration that varies markedly by brain region and cell type. Using high-resolution epigenetic profiling of postmortem human cell types we identify a pathogenic cascade linking cell type specific enhancer activity to somatic CAG expansion, and toxicity to epigenetic dysregulation. Enhancers regulating mismatch-repair (MMR) gene expression explain the specificity of expansion. In the second, toxic phase of HD we identify two distinct epigenetic mechanisms that disrupt regulation of hundreds of genes in the majority of HD MSNs, including several that cause haploinsufficient neurological disorders. Together, these data unify enhancer function, impaired DNA demethylation, and transcriptional dysregulation into a single model highlighting therapeutic opportunities that combine inhibition of somatic CAG expansion with restoration of neuronal DNA demethylation.

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Testing the “ticking DNA clock” model for HD pathogenesis

Steven McCarroll, PhD, Broad Institute & Harvard Medical School & Howard Hughes Medical Institute

Three years ago at this conference, our lab presented data that suggested a surprising model for HD pathogenesis: that the disease-causing CAG repeat is biologically innocuous in the form in which it is inherited and even after substantial somatic expansion; that its toxicity begins as it crosses a surprisingly high threshold of about 150 CAGs; and that this toxicity is fast and intense (rather than slow and indolent) and experienced sequentially (rather than simultaneously) by the individual neurons in the striatum.
Here we will present new data that tests this model in a variety of settings, including: different brain areas; the longstanding question about the relationship of nuclear HTT inclusions (aggregates) to HD pathogenesis; and the effects of non-canonical (loss-of-interruption) HTT alleles. Our analyses of CAG-repeat tracts, nuclear inclusions and genome-wide RNA expression in hundreds of thousands of cells from more than 50 people with HD suggest that the “ticking DNA clock” model offers a simple, unifying explanation for diverse pathologies and genetic effects in HD.

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Multimodal spatial transcriptomics determines repeat expansion, huntingtin aggregation, and selective cortical neuron loss in Huntington’s disease

Bogdan Bintu, PhD, University of California, San Diego

Huntington’s disease (HD) is caused by CAG expansion in HTT, yet how somatic repeat instability and huntingtin aggregation relate to selective cell loss in the human brain remains unclear. We have developed a multimodal spatial transcriptomics approach that enables defining transcriptional programs with subcellular resolution, somatic CAG-repeat lengths, and six other pathology marks including huntingtin aggregates in every cell of intact brain sections. Imaging 428,173 cells in HD cortex revealed selective vulnerability: L5–6 NP and L6b deep-layer excitatory neurons undergo >50% loss, closely linked to very large (>380±55) somatic expansions. Intranuclear aggregation was most prevalent at intermediate somatic repeat expansion (220-300 CAGs) and was accompanied by broader transcriptional changes. In contrast, chandelier and somatostatin+ inhibitory interneurons are lost despite only modest repeat expansion or aggregation. These data provide a comprehensive resource and establish a broadly applicable framework for connecting repeat expansion and protein pathology across diverse cell types.

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Unveiling TCERG1 biology: A key transcriptional and splicing regulator in Huntington’s disease

Carlos Suñe, PhD, Spanish National Research Council (IPBLN-CSIC)

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RNA dysregulation in aged neurons

Gene Yeo, PhD, MBA, University of California, San Diego

Huntington’s disease (HD) is primarily driven by the length of the polyglutamine (polyQ) tract encoded by the CAG repeat in the HTT gene, yet this factor alone does not fully explain variability in onset and progression. Genome-wide studies have revealed a complex network of genetic modifiers acting through distinct molecular pathways. Among these, mismatch repair (MMR) genes accelerate HD onset by promoting somatic CAG-repeat expansion. However, recent evidence highlights non-MMR modifiers that influence HD independently of somatic expansion, implicating transcriptional regulation and RNA processing as critical contributors to pathogenesis.
A key example is TCERG1 (Transcription Elongation Regulator 1), a transcriptional and splicing regulator that interacts with mutant huntingtin (mHTT) and mitigates its toxicity in rodent models. Structurally, TCERG1 contains a hexanucleotide repeat region (QTR) encoding a glutamine/alanine-rich tract. Multiple studies demonstrate that QTR length strongly correlates with age at onset: longer repeats associate with earlier onset, while shorter repeats delay symptoms. Recent GWAS identified two independent TCERG1 variants linked to QTR length and disease onset, reinforcing its role as a modifier acting through mechanisms distinct from CAG expansion.
Beyond genetic association, TCERG1 plays a pivotal role in neuronal biology. We found that TCERG1 influences the synthesis and processing of pre-mRNA in neuronal genes essential for morphogenesis and neurite outgrowth. Additionally, TCERG1 affects dendritic development in SH-SY5Y cells and primary mouse neurons. More recently, we discovered that TCERG1 contributes to the architecture of specific nuclear bodies and the biogenesis of key alternative splicing ribonucleoproteins localized within these structures.
These findings underscore the emerging importance of non-MMR pathways in HD, particularly those involving transcriptional elongation and splicing regulation. Elucidating how TCERG1 repeat architecture and nuclear functions modulate neuronal stability may reveal novel therapeutic targets and advance precision medicine strategies for HD. Aging is one of the most prominent risk factors for neurodegeneration, yet the molecular mechanisms underlying the deterioration of old neurons are mostly unknown. To efficiently study neurodegeneration in the context of aging, we transdifferentiated primary human fibroblasts from aged healthy donors directly into neurons, which retained their aging hallmarks, and we verified key findings in aged human and mouse brain tissue. Here we show that aged neurons are broadly depleted of RNA-binding proteins, especially spliceosome components. Intriguingly, splicing proteins—like the dementia and ALS-associated protein TDP-43—mislocalize to the cytoplasm in aged neurons, which leads to widespread alternative splicing. Cytoplasmic spliceosome components are typically recruited to stress granules, but aged neurons suffer from chronic cellular stress that prevents this sequestration. If time permits, I will present new data on the source of RNA dysfunction during aging that drives this aging-linked deterioration.

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Functional and adaptive roles of polyglutamine and other sequence features of the yeast Mediator Complex subunit Med15

Jan Fassler, PhD, University of Iowa

Med15 is a general transcriptional regulatory subunit functioning within the tail module of the RNA Pol II Mediator Complex. The Saccharomyces cerevisiae Med15 protein has a well-structured N-terminal KIX domain, three activator binding domains (ABDs) and several naturally variable polyglutamine (poly-Q) tracts (Q1, Q2, Q3) embedded in an intrinsically disordered central region, and a C-terminal mediator association domain (MAD). We investigated how the presence of ABDs and changes in length and composition of poly-Q tracts influences Med15 activity using phenotypic, gene expression, transcription factor interaction and phase separation assays of truncation, deletion, synthetic and naturally occurring variant alleles. Robust Med15 activity required at least the Q1 tract, and the length of that tract modulated activity in a context-dependent manner. Reduced transcriptional activation due to Med15 Q1 tract variation correlated with reduced TF:Med15 interaction strength. Finally, we found that natural variant MED15 alleles from domesticated wine yeasts were adaptive, with changes to the Q tracts modulating the transcriptome and contributing to improvements in fermentation activity.
We found that the Q1 tract was not crucial for liquid-liquid phase separation (LLPS) of Med15 with TFs, although substitution of the Q tract with leucines caused a striking non-droplet aggregation phenotype. The major contributor to LLPS of Med15 with the Gcn4 TF was ABD1. Mutation of W196 and other aromatic residues within ABD1 reduced the interaction between Med15 and Gcn4 in two-hybrid assays and changed the morphology or eliminated LLPS with the Gcn4 TF.
The structure of the Mediator Complex and most Mediator subunits are conserved throughout Eukarya. However, except for the well-structured KIX domain, the amino acid sequence of Med15 is not conserved. A full-length human MED15 cDNA failed to complement any phenotypes characteristic of med15 deletion strains, however Med15 hybrids in which the N terminal and central Q rich regions of human MED15 were fused to the S. cerevisiae MAD domain were partially functional. In preliminary work, we found that the N terminal 329 amino acids of human Med15 formed non-droplet aggregates with yeast Gcn4. The merits of the yeast system for elucidating the role of Med15 in Huntington’s disease will be discussed.

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Pathogenesis studies of neurodegenerative diseases: The rare informs the common

Huda Y Zoghbi, MD, Howard Hughes Medical Institute

Protein misfolding and accumulation are a common feature of a number of neurodegenerative diseases, from the idiopathic and all-too-common Alzheimer disease to the rare, inherited spinocerebellar ataxias. Studying spinocerebellar ataxia type 1 (SCA1), together with Harry Orr, we discovered it is caused by expansion of a translated CAG repeat that encodes glutamines in Ataxin-1; this discovery made it possible to generate a mouse model in which a full-length protein bearing an expanded polyglutamine tract was targeted into the endogenous Ataxin-1 locus, closely reproducing the human disease. These Sca1154Q/+ mice taught us that the polyglutamine expansion makes mutant Ataxin-1 resist degradation, which slowly increases its steady-state levels, driving pathogenesis. We also discovered that modest reductions of Ataxin-1 mitigate disease. We began to dissect the factors that contribute to the vulnerability of specific neurons in SCA1 and discovered that Capicua (CIC), one of Ataxin-1’s native partners, drives Purkinje cell toxicity. More recently, we investigated why the broadly expressed Capicua drives degeneration only in Purkinje cells and were surprised to discover the underlying mechanism and the role of the ATXN1-CIC complex in other brain regions. Finally, learning from SCA1 we ventured into the study of other proteopathies, especially Alzheimer and Parkinson disease. Focusing on tau, we performed cross-species genetic screens and identified modulators of tau levels that helped us gain new insight into tau regulation and biology. We are currently building on these latest discoveries to develop potential therapeutic strategies to help people with Alzheimer disease and related dementias.

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Single-molecule tracking of sequence-dependent mismatch repair in vitro and in vivo

Taekjip Ha, PhD, Boston Children’s Hospital & Harvard Medical School

Mismatch repair is essential for faithful transmission of genetic information and maintenance of genome integrity, but it is also known to be involved in DNA-repeat expansion that is considered to be responsible for various neurodegenerative disorders. We currently lack a high resolution and comprehensive understanding of how early steps of mismatch repair are dependent on mismatch type and sequence context. To address this knowledge and technological gap, we developed a high throughput method to determine in vivo mismatch repair efficiency of thousands of different mismatched sequences in parallel. We used single molecule fluorescence assays in vitro to dissect individual steps of mismatch recognition and sliding clamp formation by E. coli MutS under diverse sequence contexts and supercoiling. We have expanded our analysis to human MutSband CAG loops that are associated with Huntington disease. These integrated approaches promise to reveal the detailed early steps and intermediates that lead to repeat expansion and may also be used to study the effect of therapeutic interventions against repeat expansion.

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Bioengineered multicellular brain models for novel discovery

Alice Stanton, PhD, Massachusetts General Hospital & Harvard Medical School

Up to 1 in 6 people worldwide, 1 billion, are estimated to have a neurological disorder, costing over $500B in the US alone. For most neurological diseases there is still no pharmacologic treatment available that can slow or stop neuronal damage. New models are critically needed that more faithfully recapitulate human disease, to enable enhanced discovery of biomarkers and targets, more translatable therapeutic development, and personalized drug screening. Recent advances in understanding underlying genetic risk variants and cell type-specific profiling are shining new light into potential mechanisms. However, systems are needed to functionally assess the consequences of these variants, dissect disease etiology, and evaluate potential interventions. Patient heterogeneity complicates the interpretation of human samples and many putative disease mechanisms involve regulatory processes not well-conserved in animal models. Therefore, to establish an advanced preclinical model of the brain, we have developed a multicellular integrated brain model, miBrain, that incorporates brain-resident immune, neuronal, glial, and vascular cell types of human patient-specific origin and with 3D tissue structural organization. To construct this model, we differentiated each of the six major brain cell types from iPSCs, encapsulated them in a novel biomaterial scaffold with cell-instructive and brain-mimetic cues, Neuromatrix Hydrogel, and optimized a modular co-culture method to form a 3D engineered brain tissue mimic. miBrains consist of 3D immune-glial-neurovascular units with enhanced cell- and tissue-scale phenotypes inclusive of more mature glial cells, microglial immune cells with upregulated homeostatic signatures in healthy conditions, contiguous lumenized vascular networks and blood-brain barrier (BBB), neurovascular units, and interconnected, myelinated neuronal networks. The modularity of the platform enables the inclusion of defined cellular subtypes to tailor the model to specific disease conditions. We have harnessed these systems to model APOE4 risk for Alzheimer’s disease, recapitulating canonical disease hallmarks of increased reactive astrocytes, amyloid aggregates, and neuronal tau phosphorylation. Thus, we have established a novel preclinical brain model with broad utility that can be paired to in silico analyses for enhanced causal inference. This system could be harnessed to probe a wide range of genetic variants, identify nodes for intervention, and test in silico predictions towards enhanced therapeutic discovery.

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In vivo correction of expanded CAG/CTG repeats using the CRISPR/Cas9 nickase

Alvaro Murillo Bartolome, UK Dementia Research Institute at Cardiff University

Expanded CAG/CTG repeats cause over 15 different diseases that all remain without a disease-modifying treatment. Because repeat length accounts for most of the variation in disease severity, contracting them presents an attractive therapeutic avenue. Here, we show that the CRISPR-Cas9 nickase targeted to CAG/CTG repeats leads to efficient contractions in Huntington’s disease patient-derived neurons and astrocytes, and in myotonic dystrophy type 1 patient-derived neurons. The approach is allele-selective and free of detectable off-target mutations. Striatal injection of the Cas9 nickase in a mouse model for Huntington’s disease using adeno-associated viral vectors led to contractions in over half the infected cells. Upon injection, we observed a reduction in the number of inclusion bodies, improved transcriptome, and ameliorated locomotion. The effects were greater than expected from the contractions induced and suggest that non-cell autonomous mechanisms may be involved. Our results provide the proof-of-concept that correction of CAG/CTG repeats can improve Huntington’s disease phenotypes in vivo.

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The radicalization of drug discovery

Presentation not made available by the presenter

Gregory L Verdine, PhD, Harvard University

The field of drug discovery stands at a watershed moment of scientific, medical, and commercial opportunity. Realization of this opportunity will require radical innovations that fundamentally expand the functional capabilities of therapeutic interventions and management of the attendant risks. This talk will focus on the discovery, development, and deployment of radically new therapeutic modalities, inspired by nature, that thrust the field forward in non-obvious, impactful, and exciting new directions.

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Targeting repeat expansions with synthetic gene regulators

Aseem Z Ansari, PhD, St. Jude Children’s Research Hospital

Selective control of gene expression with small molecules has been a long-standing goal at the interface of chemistry and medicine. Small molecule modulators of proteins that enable gene transcription, including kinases, chromatin-modifying enzymes, and transcription factors (TFs) have proven invaluable as mechanistic probes and therapeutic agents. However, these molecules perturb gene regulatory processes broadly, often eliciting adverse outcomes and operating within narrow therapeutic ranges. We have developed sequence-targeted synthetic gene regulators (SynGRs) that circumvent these limitations. Built with programmable DNA-binding polyamides, first-generation SynGRs were employed to inhibit gene expression by blocking the binding of TFs to regulatory sites. By contrast, gene-targeting chimeras (GeneTACsTM) that function as molecular glues to recruit the transcriptional machinery to targeted genes are designed to stimulate expression of desired gene(s). Since our first report in 2000, integrating the principles of cooperative assembly, accrued selectivity, and combinatorial regulatory control has yielded tunable SynGRs that regulate single disease-driver genes and are being developed by Design Therapeutics as first-in-class therapeutic agents. We have applied this class of regulators to repeat expansion-driven diseases, focusing first on (GAA)n trinucleotide repeats that cause Friedreich’s ataxia (FA/FRDA). Currently, we are developing molecules that target other repeat expansions linked to an array of diseases and disorders, including Huntington’s disease. Our early results indicate that the ability to rationally “drug” disease-driver genes is now within reach.

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RNA trans-splicing as an enabling technology for allele-corrective HTT repair in Huntington’s disease

Beatriz Osuna, PhD, Tacit Therapeutics

Huntington’s disease (HD) is driven by a CAG expansion in HTT that produces toxic mutant huntingtin while reducing wild-type huntingtin dosage and function, presenting a multifaceted therapeutic challenge. Spliceosome-mediated RNA trans-splicing offers a targeted RNA repair strategy to replace the mutant HTT exon while preserving endogenous gene regulation, avoiding the safety, immunogenicity, and expression-control limitations associated with traditional genome-editing and gene-replacement approaches. Tacit Therapeutics has built an end-to-end discovery engine that enables rapid engineering and screening of Splicing-Directed Repair RNA molecules using design, build, test, learn cycles that leverage principles in RNA processing, synthetic biology, and high-throughput experimentation in a tight loop with computational tools. Using this discovery engine, we have engineered optimized RNA trans-splicing systems that consistently achieve >50% HTT RNA repair in vitro in HEK293T cells and iPSC-derived glutamatergic neurons harboring a 50x CAG-repeat expansion. Following a single AAV9 administration in a Huntington’s disease mouse model, we observe up to 72% HTT RNA repair in the brain. These levels of repair support substantial replacement of mutant transcripts while preserving physiological regulation of HTT expression. Comprehensive safety assessment demonstrates a favorable profile for RNA trans-splicing in the HD context. Transcriptome-wide analyses reveal no evidence of dysregulated gene expression in vitro or in vivo, supported by differential expression analyses and a custom mis-trans-splicing detection pipeline. Immunohistochemical analysis further shows no perturbation of neuronal integrity or induction of immune activation in vivo. Together, these results support RNA trans-splicing as a dual-mechanism therapeutic approach for HD that simultaneously reduces toxic mutant huntingtin and restores wild-type huntingtin expression from repaired transcripts, while highlighting the potential of precision RNA repair as a disease-modifying strategy for Huntington’s disease and other inherited neurological diseases.

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HD genetic modifier vignettes

Jim Gusella, PhD, Massachusetts General Hospital & Harvard Medical School

The GeM-HD Consortium operates with the conviction that clues to the mechanism of HD resulting in disease-modifying treatments can be gleaned from the genetic make-up of the HD population. Our genome-wide association studies (GWAS) of age at clinical landmarks in HD have implicated somatic instability of the causative HTT CAG repeat as a critical rate-determining element of the HD trajectory and pointed to several DNA repair genes as potential therapeutic targets. These GWAS have also identified a comparable number of genes not directly involved in DNA handling whose mechanism of HD modification remains uncertain. The most recent GeM-HD Consortium GWAS of ~11,700 HD individuals also provided evidence for cell-type and clinical-measure specificity of some modifier effects. We have further explored modifier effects in the genotyped participants using additional strategies. These include examining phenotypic variation across the Huntington’s Disease Integrated Staging System (HD-ISS), including the rate of phenotypic change at each stage, assessing potential genetic interactions among the age at landmark findings, exploring the possibility of rare strong effect modifiers in phenotypically extreme individuals, and digging more deeply into the HTT region.

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Whole genome sequencing of Enroll-HD participants: An initial analysis

Qingqin Serena Li, PhD, CHDI

In collaboration with Regeneron, we have undertaken whole-genome sequencing (WGS) of Enroll-HD samples. To date, 18,874 samples have been sequenced to increase power for commonvariant analyses and to enable interrogation of rare and ultra-rare variation. Prior GeM-HD GWAS analyses have implicated the mismatch-repair (MMR) pathway, as well as genes involved in chromatin remodeling and transcriptional regulation, in the onset of clinical landmarks and in blood-based somatic instability of HTT CAG repeats.
Using Enroll-HD/REGISTRY array data (GWA3–6) together with Enroll-HD WGS data for newly sequenced participants, we performed a GWAS meta-analysis (total N ≈ 18,000) across three cohorts for 12 phenotypes. These included age of onset (AOO) for eight clinical symptom domains—motor, cognitive, and six psychiatric features—as well as four definitions of HD AOO. Using a time-to-event mixed-effects survival model, we identified 33 genome-wide significant independent signals (linkage disequilibrium (LD) r < 0.1) across ~11 genomic regions and 11 traits (excluding self-reported onset), implicating MMR genes in the onset of psychiatric phenotypes and revealing additional independent signals within known modifier loci. Exome-focused rare-variant gene-level analyses in a single WGS cohort (N ≈ 14,000) identified 39 genome-wide significant associations across 12 traits (significant omnibus Cauchy test after multiple-testing correction, p < 3.95 × 10–7, requiring a minimum gene-level minor allele count of 20). These results again highlighted MMR genes and additionally implicated novel genes involved in immune and inflammatory signaling, chromatin remodeling, and transcriptional regulation across multiple phenotypes. FAN1 was associated with apathy, perseverative/obsessive behaviors, cognitive decline, motor onset, and HD diagnosis, while PMS1 and POLD1 were associated with motor onset and HD diagnosis only. In conclusion, both common- and rare-variant analyses converge on the MMR pathway as a key contributor to HD symptom onset and diagnosis, while also nominating novel loci and novel variants within known loci for further investigation. The data and CHDI analyses will be made available to the HD research community.

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Rare mutations in the DNA mismatch repair pathway affect the onset of motor neuron symptoms in Huntington’s disease

Sahar Gelfman, PhD, Regeneron Genetics Center

Large genetic association studies of age at onset of Huntington’s disease (HD) implicated DNA damage response and mismatch repair proteins as playing a role in disease onset. Studies of rare coding mutations may reveal mechanisms that modify disease onset and progression among patients with Huntingon’s disease. We performed whole genome sequencing in 18,874 samples available from the Enroll-HD cohort and conducted genetic association analyses using both genome-wide common variation as well as the gene-level burden of rare coding variants. We tested for genetic association with the age at motor symptom onset, HD diagnosis age, and additional clinical scores that correspond to progressive disease stages. In particular, ages at Total-Functional-Capacity (TFC) 6, Diagnostic Confidence Level (DCL) 4, and HD Integrated Staging System (HD-ISS) Stage 3 were also modeled as outcomes.
Gene-level burdens of rare predicted-deleterious protein coding variants were significantly associated with age at motor symptoms in four genes, namely PMS1, SH3BP2 (near the HTT locus), FAN1 and POLD1. Deleterious missense and putative loss of function (pLoF) variants in both POLD1 (effect=1.29 SD, P=4.14×10-9) and PMS1 (effect=0.60 SD, P=1.88×10-8) were associated with delayed onset. We found that, on average, pLoF variants in POLD1 delay age at motor symptom onset by 20 years in heterozygous subjects (effect=+2.09 SD, P=1×10-5), and PMS1 pLoF variants delay the onset of motor symptoms by 7 years (effect=+1.03 SD, P=2.09×10-3). Finally, we find that loss-of-function variants in FAN1 significantly accelerate motor symptom onset by 10 years (effect = -0.95 SD, p=2.48×10-10). Here we report for the first time genome sequencing of the full Enroll-HD sample set, giving the first view of the effects of rare coding variation on HD clinical phenotypes, and the direction of effect. Carriers of a pathogenic HTT expansion and rare loss-of-function variants in POLD1 and PMS1 present substantial delayed disease onset for HD, suggesting the benefit of inhibiting these proteins as potential therapeutic targets.

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Structural variation, tandem repeats and new disease associations

Evan Eichler, PhD, University of Washington School of Medicine & Howard Hughes Medical Institute

Advances in long-read sequencing have enabled telomere-to-telomere (T2T) sequencing of genomes, essentially providing, for the first time, sequence resolved chromosomes. This advance has meant that all forms of genetic variation can be discovered, including previously underappreciated complex patterns of structural variation (SV) in regions previously regarded as inaccessible to sequence and assembly. I will present our most recent work with respect to long-read sequencing of diverse human genomes and show how this data is being used to fully characterize the structure and population distribution of tandem repeat loci, such as the Huntington’s disease locus. I will present data on long-read sequencing of >1000 individuals recruited through the All of Us program with electronic health record data. I will show how these data have been used to discover new candidate SVs that can be imputed or directly genotyped in larger short-read data sets to discover novel disease association candidates and to discover expressed quantitative loci that affect gene expression. This approach provides a strategy to discover causal variants more likely associated with human phenotypic traits.

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URSA (Unscheduled Repair DNA Synthesis Assay), a potential target engagement and pharmacodynamic assay for Huntington’s disease

Paolo Beuzer, PhD, CHDI

A crucial gap for the development of mismatch repair (MMR) therapies for halting HTT CAG somatic instability (SI) for the treatment of Huntington’s disease (HD) is the availability of pharmacodynamic and target engagement assays to quantify modulation of MMR activity. Whereas SI can be measured in HD blood cells by tracking mHTT CAG-repeat expansion over time, currently the rate of change appears to require 1 to 2 years to detect a significant SI expansion. As an alternative to measuring the infrequent change of CAG-repeat length we developed URSA (Unscheduled Repair Synthesis Assay), a quantitative PCR-based assay that measures unscheduled DNA synthesis at specific genomic loci such as HTT. We found by quantifying the incorporation of 5-ethynyl-2’-deoxyuridine (EdU) at the HTT locus, URSA provides a highly sensitive and quantitative measure of DNA damage response (DDR) activity at the mHTT within days.
We validated our novel URSA assay in clinically relevant HD patient blood cells, and in different preclinical cell models including human HD neurons. Our results show that MMR activity at the mutant HTT allele is detectable, correlates with inherited CAG-repeat length, and is significantly more frequent than changes in CAG-repeat length. Modulation of MSH3/MutSbwith different modalities (siRNA, shRNA, small molecule MutSbATPase inhibitors, and knock-out) abrogates unscheduled DNA synthesis and URSA signal at the mHTT locus. URSA is being implemented for mechanistic studies, and for further advancement as a candidate SI surrogate pharmacodynamic assay for use in clinical studies.

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From populations to cells: Precision health through human molecular profiling at scale

Claudia Langenberg, MD, PhD, FFPH, EMBO, FMedSci, Queen Mary University of London & Berlin Institute of Health at Charité–Universitätsmedizin Berlin

Application of different omic technologies is now feasible at population scale. This talk will present examples of how the integration of different omics in large patient and population studies can help to predict disease risk, understand mechanisms, and reveal shared connections between rare and common diseases. Studies include different technologies and an investigation into how these can be combined and how their complementarity can be employed for synergistic insights into human health.