Disease indication
The mechanism was never in doubt — getting the drug into muscle was
Disease-modifying: Remove or silence the expanded CUG RNA and let the sequestered splicing factors go back to work. The mechanism has been understood for three decades; until conjugate chemistry arrived, nothing could reach skeletal muscle in sufficient quantity to test it.
Nothing yet alters the course of DM1 — but unlike Parkinson's, no completed trial has yet tested the central hypothesis and rejected it.
The CTG expansion in DMPK was identified in 1992 by three groups at once. The mechanism has not been in serious doubt since; the delivery problem has.
Conjugate chemistry produced measurable DMPK knockdown and splicing correction in patient muscle biopsies — the molecular milestone no Parkinson's disease-modifying programme ever reached.
A single pivotal, not two, with a molecular surrogate available at around a year — the rare-disease pathway in miniature.
The same three axes as Parkinson's, and close to the mirror image. Construct validity is high almost everywhere, because the causal mutation is known and the models carry it. The predictive column is empty for a quite different reason — not tested and failed, but not yet tested to a conclusion.
| Model | FaceDoes it look like the disease? | ConstructDoes it arise the same way? | PredictiveCorrect the defect |
|---|---|---|---|
One completed failure — and it failed for a reason you can point at. The drug never reached muscle. Everything since has been an attempt to fix delivery rather than mechanism.
| Intervention | Rested on | Reached | Outcome |
|---|---|---|---|
Delpacibart etedesiran (AOC 1001) Avidity Biosciences · Anti-transferrin-receptor antibody conjugated to siRNA against DMPK | HSA-LRPatient myotubes | Phase 3 MARINA → HARBOR · 2024 | Ongoing |
DYNE-101 Dyne Therapeutics · Anti-transferrin-receptor Fab conjugated to an antisense oligonucleotide | HSA-LRPatient myotubes | Phase 1/2 ACHIEVE · 2024 | Ongoing |
PGN-EDODM1 PepGen · Cell-penetrating peptide conjugated to a phosphorodiamidate morpholino oligomer | HSA-LRPatient myotubes | Phase 1 FREEDOM-DM1 · 2024 | Ongoing |
Tideglusib (AMO-02) AMO Pharma · GSK-3β inhibition | DMSXL | Phase 2/3 REACH-CDM · 2023 | Missed primary |
IONIS-DMPK-2.5Rx Ionis / Biogen · 2'-MOE gapmer antisense oligonucleotide against DMPK RNA | HSA-LR | Phase 1/2 IONIS-DMPK-2.5Rx · 2017 | Failed |
rhIGF-1 / rhIGFBP-3 Investigator-led · Anabolic growth-factor signalling in muscle | HSA-LR | Phase 2 rhIGF-1/rhIGFBP-3 in DM1 · 2011 | Failed |
Expresses roughly 220 CTG repeats in the untranslated region of a human skeletal actin transgene. Reproduces nuclear RNA foci, muscleblind sequestration, the characteristic mis-splicing, and frank myotonia — in skeletal muscle only.
A mouse carrying the same kind of toxic repeat that causes DM1, put into a muscle gene. It gets stiff muscles that will not relax — real myotonia — and the same splicing errors patients have. What it does not get is the heart and brain involvement, which is much of what makes DM1 dangerous.
The workhorse for target engagement, and unusually trustworthy at that job: correcting splicing here has predicted correcting splicing in patients. It says nothing about whether corrected splicing produces a functional benefit, which is exactly the question the ongoing Phase 3s exist to answer.
Human skeletal actin promoter driving ~220 interrupted CTG repeats in the 3' UTR. Recapitulates ribonuclear foci, MBNL1 sequestration and CLCN1 mis-splicing with electrically demonstrable myotonia. High construct validity for the RNA gain-of-function mechanism; no cardiac, CNS, somatic instability, or DMPK-locus context.
Rare disease rewrites the arithmetic: trials an order of magnitude smaller than Parkinson's, a single pivotal rather than two, and a molecular surrogate that can read out long before function would.
The molecular surrogate is what keeps this affordable. Splicing correction is readable in a muscle biopsy at around a year, so the pivotal does not have to wait out the years of functional decline that a Parkinson's progression trial requires.
305 patient-years against 130 for a symptomatic programme. Cost grows more slowly than exposure because the fixed enrolment cost of each participant — screening, baseline imaging — is paid once however long they are then followed. The goal, not the molecule, still sets the budget.
Citedenrolment, duration and study counts, from named trials.Assumptionthe two cost parameters below.Computedeverything else.
| Phase | Design | N × studies | Duration | Patient-years | Modelled cost |
|---|---|---|---|---|---|
| Phase 1 | SAD / MAD, healthy volunteers Conjugated oligonucleotides carry platform-level safety questions, so first-in-human work is not shortened by the rare-disease setting. Conventional first-in-human designmoderate confidence | 40 | 9 mo | 30 | $1.1M–$1.8M |
| Phase 1/2 | Dose-escalation in patients with biopsy readout Sized after MARINA and ACHIEVE. Muscle biopsy gives target engagement and splicing correction directly, so very small cohorts still answer the central question. MARINA (Avidity) and ACHIEVE (Dyne) Phase 1/2 designsmoderate confidence | 50 | 1 yr | 50 | $1.6M–$2.6M |
| Phase 3 | Single pivotal, surrogate plus functional endpoints Sized after HARBOR. A splicing surrogate can support accelerated approval at around a year while functional confirmation continues — the structural reason this costs a fraction of a Parkinson's progression trial. HARBOR (Avidity) Phase 3 designmoderate confidence | 150 | 1.5 yr | 225 | $6.3M–$11M |
| Total | 3.3 yr of clinical development, treating phases as sequential | 305 | $9.0M–$15M |
Model assumptions, not citations — the only free parameters here. The fixed component covers screening, baseline imaging and randomisation, incurred once per participant; the running component covers visits, monitoring and site fees for each year on study. Splitting them matters: a single rate per patient-year would price short symptomatic trials far below what pivotal trials actually cost.
Calibration: priced this way a single pivotal trial in this programme comes to $3.3M–$5.3M, against published pivotal trial costs of $12–33M (median $19M) across all indications. A rare-disease pivotal enrolling around 150 participants belongs well below that all-indication median — and does. The gap is the point: recruiting from a population of roughly 1 in 8,000 buys a much cheaper trial than a common disease requires. Moore et al., JAMA Internal Medicine 2018.
Programme cost divided by a 17% likelihood of approval from Phase 1 in rare disease — what one success costs once the failures are paid for. BIO / Informa / QLS, Clinical Development Success Rates — rare-disease programmes clear Phase 1 to approval far more often than the all-indication average.
Read this one carefully: Rare-disease success rates are lifted by oncology and by enzyme-replacement in diseases with a missing protein to replace. DM1 is neither: it is a first-in-class RNA-targeting programme in a multisystem neuromuscular disease, and the one DM1 programme that has run to a conclusion failed. Read 17% as the optimistic end of the range, not as this indication's rate.
These are portfolio figures spanning all of R&D and already carry the cost of failure, so they are not comparable with the per-programme clinical costs above — they are the order of magnitude those costs roll up into.
DM1 has become the test case for whether a mechanistically-anchored biomarker can carry a neuromuscular drug all the way to approval.
Splicing correction can be measured in a muscle biopsy and maps directly onto the causal mechanism, making it a candidate surrogate for accelerated approval. Parkinson's spent thirty years without any equivalent. If a DM1 drug is approved on splicing, it sets a precedent for every repeat-expansion disease behind it.
Sponsor disclosures on accelerated-approval strategy
The first programme failed because oligonucleotides do not reach skeletal muscle in useful quantity. Conjugating them to transferrin-receptor binders fixed that, and the same chemistry is now being applied across muscle disease. It is a rare case of a well-diagnosed translational failure being engineered around.
Avidity and Dyne platform disclosures
The CTG tract expands within tissues over a patient's lifetime, and repair factors such as MSH3 modify how fast. Targeting instability rather than its RNA product would attack the disease a step earlier — an approach shared with Huntington's and the other repeat-expansion disorders.
Somatic instability and DNA-repair modifier literature