Will the FDA Approve Deramiocel for Duchenne by August 2026

Based on current clinical trajectories and regulatory communications, it is highly likely that the U.S. Food and Drug Administration (FDA) will grant approval for deramiocel to treat Duchenne muscular dystrophy (DMD) by the Prescription Drug User Fee Act (PDUFA) target action date of August 22, 2026. The FDA has lifted its previous Complete Response Letter and accepted Capricor Therapeutics' resubmitted Biologics License Application following highly successful Phase 3 trial data showing the therapy significantly slows both cardiac and skeletal muscle decline. While a recent commercial distribution lawsuit introduces complexities for the drug's market launch, Capricor and regulatory analysts have confirmed this legal dispute will not delay the FDA's ongoing review timeline.

The Evolving Crisis of Duchenne Muscular Dystrophy

To understand the intense anticipation surrounding deramiocel, one must first understand the devastating progression of Duchenne muscular dystrophy. DMD is a severe, X-linked genetic disorder that occurs in approximately one in every 3,500 male births, affecting an estimated 15,000 to 20,000 boys and young men in the United States ¹¹.

The disease is caused by a genetic mutation that prevents the body from producing functional dystrophin, an essential structural protein located in muscle cells ²³. Dystrophin acts as a shock absorber; without it, ordinary muscle contractions cause repeated micro-tears in the muscle fibers ²⁵. Over time, this chronic injury triggers a relentless inflammatory response. The immune system attempts to repair the damage but is overwhelmed, leading to a process called fibrosis, where healthy muscle tissue is progressively replaced by useless fat and fibrous scar tissue ²⁴.

Historically, boys diagnosed with DMD lost the ability to walk independently by their early teenage years and typically succumbed to respiratory failure in their late teens or early twenties ⁵⁶. However, advances in modern medicine - specifically the widespread use of nocturnal non-invasive ventilation and aggressive corticosteroid regimens - have dramatically improved respiratory outcomes ⁷. Because patients are living longer, the disease has the time to heavily impact the heart muscle. Today, deterioration of the heart muscle, known as cardiomyopathy, eventually leads to heart failure and is the leading cause of death in the DMD population ⁴¹⁰⁸.

Despite this shift in mortality, there is currently no approved therapy that specifically targets the cardiac component of DMD ⁸⁹. Current cardiac management relies on borrowing therapies from general adult heart failure protocols, such as ACE inhibitors and beta-blockers, which do not address the underlying pathology of DMD ⁸. The DMD community is waiting for a disease-modifying treatment capable of preserving the heart, which is precisely what deramiocel aims to deliver.

The Science of Deramiocel: A Biological Paradigm Shift

The DMD therapeutic landscape has recently been dominated by the pursuit of gene therapy and RNA-targeted exon skipping. These approaches attempt to force the body to produce a truncated, partially functional version of the dystrophin protein ⁵¹⁰. However, these therapies are often highly specific to certain genetic mutations, meaning they cannot help all patients, and their ability to reach and heal the heart muscle remains debated ¹⁰.

Deramiocel (previously known in clinical literature as CAP-1002) represents a complete paradigm shift. It is an investigational, first-in-class "allogeneic" cell therapy ³¹¹. "Allogeneic" means the cells are sourced from a healthy donor rather than the patient, making the treatment an off-the-shelf biologic that does not require custom manufacturing for each individual ¹⁰¹².

The Role of Cardiosphere-Derived Cells (CDCs)

Deramiocel consists of cardiosphere-derived cells (CDCs), which are a rare population of stromal cells harvested from healthy donor heart tissue ³¹³. Once extracted, these CDCs are expanded in Capricor's laboratory and prepared for intravenous administration, typically given to the patient four times a year ¹⁰⁹.

Crucially, these donor cells do not graft into the patient's heart or permanently replace the damaged tissue. Instead, they act as microscopic pharmaceutical factories, communicating with the patient's own immune system ⁵¹⁰.

Modulating the Macrophages via Exosomes

The true mechanism of action for deramiocel lies in what the CDCs secrete: tiny extracellular vesicles known as exosomes ³¹³. These exosomes are loaded with therapeutic RNA and proteins that specifically target macrophages, a type of white blood cell that orchestrates the body's inflammatory response ³.

In a DMD patient, macrophages are locked in a chronic, pro-inflammatory state due to the constant tearing of dystrophin-deficient muscles ⁴. They attack the tissue, driving the fibrosis that turns muscle to scar ⁴. When deramiocel's exosomes enter the bloodstream, they are taken up by these angry macrophages and alter their genetic expression profile ³. The exosomes effectively flip a biological switch, reprogramming the macrophages from a destructive, pro-inflammatory phenotype to a healing, pro-regenerative phenotype ³¹⁴.

This immunomodulatory, anti-fibrotic, and pro-angiogenic effect calms the systemic inflammation, halts the progression of scarring, and promotes natural cellular repair processes in both the heart and the skeletal muscles ¹⁰¹⁴. Because deramiocel targets this downstream inflammatory cascade rather than the upstream genetic mutation, it is considered "mutation-agnostic" - meaning it has the potential to treat any DMD patient, regardless of the specific flaw in their dystrophin gene ⁸¹⁵.

The Regulatory Journey: From HOPE-2 to the 2025 Rejection

The pathway to FDA approval for any novel biologic is rigorous, and for a first-in-class cell therapy targeting a rare disease, the scrutiny is exceptionally high. Capricor's initial bid for approval rested primarily on data generated during its Phase 2 clinical program, which consisted of the HOPE-2 trial and its subsequent Open Label Extension (OLE).

The Promise of the Phase 2 Data

The HOPE-2 trial ran from 2018 to 2020 and enrolled 26 severely affected DMD patients ¹⁶. The results, published in The Lancet in 2022, were groundbreaking. The data showed that deramiocel provided a statistically significant benefit over a placebo in preserving upper limb function over a 12-month period ⁹¹⁶.

Furthermore, patients who transitioned into the HOPE-2 Open Label Extension - where all participants received the active drug - demonstrated sustained benefits over multiple years. At the three-year mark, patients treated with deramiocel showed a much slower decline in upper limb function (-4.1 points) compared to an external natural history comparator group (-7.8 points) ⁹¹⁰¹⁶. By the four-year mark, cardiac data revealed a near stabilization of left ventricular ejection fraction, which is unheard of in the natural progression of DMD ¹⁷.

Bolstered by this long-term evidence, Capricor initiated a rolling Biologics License Application (BLA) seeking full approval for deramiocel specifically for the treatment of DMD cardiomyopathy ¹¹⁸. The FDA initially accepted the application and granted it Priority Review, a status reserved for drugs that offer major advances in treatment for severe conditions, assigning a target action date of August 31, 2025 ¹¹¹⁹.

The July 2025 Complete Response Letter (CRL)

Despite the promising Phase 2 data and the FDA's initial acceptance, the regulatory process hit a wall in the summer of 2025. On July 11, 2025, Capricor announced that it had received a Complete Response Letter (CRL) from the FDA ⁴²⁰. A CRL is the agency's formal method of communicating that it has completed its review but cannot approve the application in its current form.

The FDA's primary objection was rooted in clinical trial design and statistical power. The agency stated that the BLA, which relied heavily on the small, 26-patient HOPE-2 study, failed to meet the statutory requirement for "substantial evidence of effectiveness" ⁴²⁰. The FDA explicitly required additional clinical data to confirm the drug's efficacy ⁴. Furthermore, because the FDA halted its review upon issuing the CRL, the agency noted that it had left portions of the Chemistry, Manufacturing, and Controls (CMC) section unreviewed, though Capricor maintained that most CMC issues had been previously addressed ²⁰.

For the DMD community, the rejection was a devastating blow ²⁰²⁴. However, Capricor was uniquely positioned to recover quickly. Anticipating the FDA's strict evidence requirements, the company had already been quietly running a massive, confirmatory Phase 3 trial.

The HOPE-3 Phase 3 Trial: A Resounding Success

The trial that ultimately salvaged deramiocel's regulatory prospects is known as HOPE-3. This was a Phase 3, multi-center, randomized, double-blind, placebo-controlled clinical trial specifically designed to provide the undeniable proof of efficacy the FDA demanded ⁷²⁵.

HOPE-3 enrolled 106 participants across 20 clinical sites in the United States ²⁵²⁶. The cohort consisted of boys and young men with an average age of approximately 15 years, encompassing both late-ambulatory patients (those struggling to walk but still on their feet) and non-ambulatory patients (those using a wheelchair) ⁶²⁵. To ensure the data isolated the effects of deramiocel, all participants were maintained on a stable background regimen of corticosteroids ²⁵.

Participants were randomized in a 1:1 ratio to receive either intravenous deramiocel (at a dose of 150 million cells per infusion) or a placebo, administered every three months for a 12-month evaluation period ⁷²⁵²⁷. Baseline demographics were well balanced between the two arms, with roughly 75% of participants already carrying a clinical diagnosis of cardiomyopathy at the start of the study ²⁵²¹.

Comparison of Clinical Trial Designs

To understand why the FDA rejected HOPE-2 but embraced HOPE-3, it is helpful to look at the scale and rigor of the two studies.

Table 1: A comparison of the HOPE-2 and HOPE-3 clinical trial designs. The larger scale and updated endpoints of HOPE-3 provided the statistical power necessary to satisfy FDA requirements. ^7162527

In early December 2025, Capricor unblinded the HOPE-3 data and announced positive topline results, reporting that the trial successfully met both its primary skeletal muscle endpoint and its key secondary cardiac endpoint with statistical significance ²⁶²². Detailed data subsequently presented at the 2026 Muscular Dystrophy Association (MDA) Clinical & Scientific Conference in Orlando, Florida, and the American Academy of Neurology (AAN) Annual Meeting in Chicago revealed the staggering extent of the drug's efficacy ²³³¹.

Skeletal Muscle Efficacy: Preserving Independence

The primary endpoint of HOPE-3 was the Performance of Upper Limb (PUL v2.0) assessment ²²²⁴. For older, non-ambulatory DMD patients, the PUL score is the most critical metric of independence. It measures the ability to perform vital daily functions, such as operating a motorized wheelchair, using a computer, or bringing food to the mouth ⁶¹⁰.

The data revealed that treatment with deramiocel resulted in an astonishing 54% slowing of skeletal muscle disease progression compared to the placebo group over 12 months (p=0.029) ⁶²²³³. This effect was consistent across different sub-levels of the PUL assessment, including a 65% slowing of disease progression at the mid-level (the elbow region) ⁶³¹.

Capricor corroborated these clinical measurements with real-world functional data. The trial utilized the Duchenne Video Assessment (DVA), which involves recording patients performing practical tasks in their own homes ²³³¹. On the highly relevant "eat 10 bites" hand-to-mouth task, patients receiving deramiocel showed an approximately 83% slowing of disease progression compared to the placebo cohort (p=0.018) ³¹. According to Dr. Aravindhan Veerapandiyan, Director of the Comprehensive Neuromuscular Program at Arkansas Children's Hospital, "No therapeutic has ever delivered a statistically and clinically meaningful difference in the upper limb functional primary endpoint of Performance of the Upper Limb" ²³.

Cardiac Efficacy: Halting Cardiomyopathy

While the skeletal muscle data was unprecedented, deramiocel's impact on the heart is what sets it apart from every other therapy in development. The key secondary endpoint for HOPE-3 was the change in Left Ventricular Ejection Fraction (LVEF), a central measure of how efficiently the heart pumps blood ⁶²².

In the overall trial population, deramiocel treatment resulted in a 91% slowing of heart function decline over 12 months compared to placebo (p=0.041) ⁶²⁷³³.

This metric effectively represents near-complete stabilization of the heart muscle ⁶²⁷.

The data was even more profound in the subgroup of patients who entered the trial with established baseline cardiomyopathy (defined by abnormal LVEF or existing scar tissue). In this advanced-disease subgroup, treatment resulted in a 3.3 percentage-point improvement in LVEF versus placebo (p=0.017) ³¹³⁴. This corresponds to a greater than 100% attenuation of the expected cardiac decline, indicating that deramiocel not only halts the damage but may allow the heart to recover lost function ³¹.

Furthermore, Capricor utilized cardiac MRI scans to measure late gadolinium enhancement (LGE), a direct biomarker for myocardial fibrosis (scarring) ³¹²⁴. The MRI analysis demonstrated a significant reduction in fibrotic segments in patients treated with deramiocel compared to placebo (p=0.022), providing structural proof to back up the functional LVEF improvements ³¹²⁴.

Assessing Safety and Tolerability

Efficacy without safety is a non-starter for FDA approval. Fortunately, the safety profile of deramiocel established in early trials held up consistently under the larger HOPE-3 investigation ²⁵²⁶²¹.

While specific numerical incidences of all adverse events from the HOPE-3 trial have not yet been fully published in peer-reviewed journals, Capricor confirmed that the safety data was consistent with prior clinical experience, which encompasses over 700 individual infusions across its research programs ²⁵²⁶³⁵. In the blinded setting of HOPE-3, investigators noted that adverse events attributed to the drug were mostly mild to moderate in severity ²⁷.

Historically, the primary risk associated with deramiocel has been an infusion-related hypersensitivity (allergic) reaction ⁹¹⁶. During the Phase 2 HOPE-2 trial, some severe allergic responses were noted. However, researchers quickly implemented a standard pre-treatment protocol involving a regimen of glucocorticoids, H1 blockers, and H2 blockers prior to the CDC infusion ¹⁶¹⁷. This simple prophylactic measure successfully prevented serious allergic reactions in subsequent patients, rendering the therapy highly tolerable for a severely affected patient population ⁹¹⁶.

Furthermore, blood tests indicated that deramiocel treatment significantly reduced the levels of creatine kinase-MB (CK-MB) - a specific biomarker for cardiac muscle damage - by a percentile difference of 29.1% compared to placebo ¹⁷²¹. This biological marker confirms that the therapy is actively reducing the breakdown of heart tissue without causing off-target toxicity.

The FDA's Pivot: Establishing the August 2026 Target

Following the release of the HOPE-3 data, Capricor entered immediate discussions with the FDA to map out a path forward ²⁵. The agency, recognizing the profound clinical implications of the new data, requested that Capricor submit the full HOPE-3 Clinical Study Report (CSR) as an amendment to the existing, paused BLA ²¹²⁶. Notably, the FDA did not demand that Capricor conduct any entirely new clinical trials, a massive win for the company and the DMD community ³³²⁶.

In early 2026, Capricor submitted the HOPE-3 data. On March 10, 2026, the company announced that the FDA had officially lifted the July 2025 Complete Response Letter and resumed its active review of the BLA ³²⁰²⁷.

The FDA classified the submission as a "Class 2 resubmission" and assigned a new Prescription Drug User Fee Act (PDUFA) target action date of August 22, 2026 ³⁸²⁷. The PDUFA date is the legal deadline by which the FDA intends to complete its review and render a final decision on approval.

In another highly positive signal for approval prospects, Capricor disclosed that the FDA stated an Advisory Committee (AdCom) meeting is not indicated at this time ¹⁹³⁹. AdComs are typically convened when the FDA is unsure about a drug's safety profile or the validity of its efficacy data and wants external expert opinions before making a controversial decision. The lack of an AdCom suggests the FDA is currently comfortable with the clarity of the HOPE-3 data ¹⁹. Additionally, Capricor noted that the FDA had "not identified any potential review issues in its response to the Company" upon accepting the resubmission ³⁸.

Should deramiocel be approved, Capricor is also in line for a significant financial windfall. Due to the therapy's designation as a treatment for a rare pediatric disease, approval would likely grant Capricor a Priority Review Voucher (PRV) ³⁸¹⁹. PRVs are highly coveted assets in the pharmaceutical industry that can be sold to other companies - often for over $100 million - to speed up the FDA review of unrelated drugs ³³⁴⁰.

The Battle for the Label: Cardiomyopathy vs. Broad DMD

One of the most critical unresolved aspects of the August 2026 decision is exactly how the FDA will label deramiocel if approved. The label dictates which patients are legally and insurance-wise eligible to receive the drug.

Originally, Capricor submitted its BLA specifically seeking full approval for the treatment of "DMD cardiomyopathy" ¹¹⁸²⁸. The company's strategy was to carve out a niche focusing purely on the heart, as the FDA had previously been hesitant to grant broad skeletal muscle approvals based on Phase 2 data.

However, the undeniable success of the HOPE-3 trial on the PUL v2.0 upper-limb skeletal muscle endpoint has fundamentally altered the company's regulatory posture. Capricor CEO Linda Marbán recently confirmed that the company is pursuing aggressive labeling negotiations with the FDA ²⁰.

"We're going to try and get not only the cardiomyopathy label, but also a skeletal muscle function or DMD label because we had such robust results in that aspect of the trial, as well," Marbán stated ²⁰.

A broad DMD label would be vastly superior commercially and practically. It would allow clinicians to prescribe deramiocel not just to stabilize a patient's failing heart, but to preserve their ability to feed themselves and operate a wheelchair. If granted, deramiocel would become the first therapy in history to address both the skeletal and cardiac manifestations of Duchenne muscular dystrophy simultaneously ³⁸.

How Deramiocel Compares to Existing Treatments

To understand the market potential for deramiocel post-August 2026, it must be compared against the current DMD treatment arsenal. For decades, the only intervention available was corticosteroids, which globally suppress the immune system to slow muscle degradation but carry severe long-term side effects like weight gain, osteoporosis, and behavioral issues ⁶²⁵.

More recently, the landscape has seen the introduction of advanced therapeutics, yet none directly address the cardiac crisis ⁸¹⁰.

Deramiocel vs. Gene Therapy (Elevidys)

The most high-profile DMD treatment currently available is Elevidys (delandistrogene moxeparvovec), an AAV-based gene therapy developed by Sarepta Therapeutics. Elevidys uses a modified virus to deliver an engineered, shortened version of the dystrophin gene ("micro-dystrophin") directly into muscle cells ²²⁹.

While Elevidys addresses the genetic root of the disease, it comes with severe limitations. First, because it uses an adeno-associated virus (AAV) vector, it can trigger massive, sometimes fatal, immune system responses. Great care and monitoring are required, and the FDA has had to mandate post-approval safety warnings regarding acute serious liver injury ²¹⁰³⁵. Second, gene therapy is currently a "one-and-done" intervention; once exposed to the viral vector, the patient develops antibodies, meaning they can likely never receive an AAV-based gene therapy again ³⁵. Finally, the micro-dystrophin produced by Elevidys is a truncated protein, meaning it does not work as efficiently as normal dystrophin, and its long-term efficacy in preserving cardiac muscle remains a subject of intense debate ¹⁰¹⁰.

Deramiocel, by contrast, relies on a well-tolerated, repeatable IV infusion of exosomes every three months ¹⁰¹¹. It avoids the toxicity associated with viral vectors, and safety data from over 700 infusions shows no significant, life-threatening side effects ³⁵.

Deramiocel vs. Exon-Skipping Drugs

The other major class of approved DMD drugs are antisense oligonucleotides (AONs), such as Exondys 51, Viltepso, and Amondys 45 ⁵¹⁰. These "exon skippers" act like molecular patches, allowing the body to skip over the mutated section of the dystrophin gene to create a partially functional protein ⁵.

The primary limitation of exon skippers is their strict mutation specificity. For example, Exondys 51 only works for the ~13% of DMD patients who have a specific mutation amenable to skipping exon 51; Viltepso only helps the ~8% amenable to skipping exon 53 ⁵. Furthermore, these drugs yield very low-level dystrophin expression, and their actual clinical benefit on muscle function remains highly controversial, with most receiving accelerated approvals based solely on surrogate biomarker data rather than functional clinical improvement ⁸¹⁰.

Because deramiocel targets the downstream inflammatory process rather than the genetic code itself, it is completely mutation-agnostic ⁸¹⁵. This means it could theoretically be prescribed alongside gene therapies or exon skippers as a combination therapy, attacking the disease from two completely different biological angles ³⁵.

Table 2: A comparative analysis of deramiocel against the primary approved genetic and RNA therapies for Duchenne muscular dystrophy. ^2351035

Global Expansion: The European EMA Strategy

While the primary focus is the August 2026 FDA deadline, Capricor is simultaneously preparing for global commercialization. In November 2024, the company announced that the European Medicines Agency (EMA) granted deramiocel two critical designations: Orphan Drug and Advanced Therapy Medicinal Product (ATMP) ¹³³⁰⁴⁴.

The Orphan Drug designation provides financial incentives, including significantly reduced regulatory fees and a guaranteed ten years of market exclusivity in Europe upon approval ¹³⁴⁴. The ATMP designation is specifically designed to facilitate the development and rapid regulatory review of novel cell-based therapies ³⁰⁴⁴. Capricor has stated its intention to pursue European approval shortly after completing its U.S. regulatory filings, aiming to tap into an estimated market of 25,000 to 30,000 DMD patients in the EU ⁴⁴⁴⁵.

Commercial Friction: The NS Pharma Lawsuit

While the clinical and regulatory pathways look exceedingly clear for deramiocel, its commercial launch has been suddenly complicated by a fierce legal battle.

In January 2022 and February 2023, Capricor entered into an exclusive distribution agreement with Nippon Shinyaku and its U.S. subsidiary, NS Pharma, to commercialize deramiocel in the U.S. and Japan ²⁸³¹. Under this agreement, NS Pharma would be responsible for marketing and distributing the drug to patients ²⁸.

However, on May 7, 2026, Capricor dropped a bombshell, filing a breach-of-contract lawsuit against Nippon Shinyaku and NS Pharma in the Superior Court of New Jersey ³¹⁴⁷. Capricor is actively seeking a preliminary injunction to rescind the distribution agreement entirely ³¹⁴⁷.

The Pricing Dispute

The crux of Capricor's lawsuit alleges a "fundamental pricing flaw" baked into the original commercialization agreement. According to legal filings, Capricor argues that the agreed-upon financial structure is not economically viable under the realities of the modern U.S. healthcare system ²⁴³¹. Specifically, Capricor claims that executing the contract as written would create "potentially hundreds of thousands of dollars in reimbursement shortfalls per dose" for patients covered by Medicare, Medicaid, or private insurance ³¹⁴⁷⁴⁸.

"Simply put, neither Capricor nor the Distributor can afford to sell the medicine at a price much lower than the costs of making and distributing it," the company wrote in its complaint ³¹. Capricor alleges that it attempted to renegotiate the pricing structure in good faith, but NS Pharma "refused to compromise" ²⁴³¹.

The Alleged "Pencils Down" Standstill

Furthermore, Capricor's lawsuit claims that NS Pharma completely abandoned its commercial responsibilities upon the issuance of the FDA's Complete Response Letter in July 2025. The complaint states that NS Pharma went "pencils down," halting all launch preparations, and failing to adequately prepare the market for the drug's eventual approval ²⁴³¹.

"I know what every additional month of delay costs [these patients], because I know what is happening inside their muscles when they cannot be treated," said Capricor CEO Linda Marbán. "There is no version of this case in which I am willing to watch NS Pharma's inaction take that away from them" ²⁴³¹.

Nippon Shinyaku and NS Pharma have forcefully denied the allegations, stating that the claims "lack merit" and asserting that they have "responded appropriately and sincerely to ensure treatment reaches DMD patients after approval" ³¹⁴⁷. In late May 2026, NS Pharma filed a motion to transfer the case from state to federal court, indicating they intend to fight the rescission of the contract ²⁴.

The Impact on the August Launch

Financial analysts and investors immediately reacted to the lawsuit, sending Capricor's stock down roughly 13% on the day of the announcement due to fears of a botched commercial rollout ³¹⁴⁹.

However, Capricor has repeatedly assured the market and patients that the legal dispute has zero bearing on the FDA's scientific review ⁴⁷⁴⁸. The PDUFA date of August 22, 2026, is completely insulated from the commercial litigation. To mitigate distribution risks, Capricor has rapidly pivoted to building its own in-house commercialization team, recently hiring a Chief Commercial Officer and a Senior VP of Market Access to prepare for an independent launch if the court grants the injunction ²⁴⁴⁸.

Capricor is currently scaling up operations at its San Diego GMP manufacturing facility to stockpile the ultra-cold chain doses required for launch, though final freezing and packaging depend on the FDA's ultimate ruling on the product's label ⁴⁸³².

Bottom line

The clinical data leaves little room for doubt: deramiocel offers a profound, statistically significant slowing of both cardiac and skeletal muscle decline in patients suffering from Duchenne muscular dystrophy. Having satisfied the FDA's demand for robust Phase 3 data via the highly successful HOPE-3 trial, Capricor's resubmitted Biologics License Application appears primed for approval by the target action date of August 22, 2026. While an ongoing breach-of-contract lawsuit with distribution partner NS Pharma introduces logistical turbulence regarding the drug's commercial pricing and rollout, the FDA's regulatory timeline remains firmly intact. If approved, deramiocel will represent a massive paradigm shift in the treatment of DMD, offering a safe, mutation-agnostic cell therapy capable of targeting the fatal cardiomyopathy that traditional gene therapies cannot reach.