Since researchers identified the expanded CAG repeat in the huntingtin (HTT) gene in 1993, the molecular cause of Huntington's disease has been clear: mutant huntingtin (mHTT) protein accumulates in the striatum, driving the progressive motor, cognitive, and psychiatric deterioration that kills people within 10 to 20 years of symptom onset. Yet no approved drug has ever slowed that progression in the estimated 75,000 people carrying the disease across the United States, European Union, and United Kingdom. The most advanced attempt was tominersen, an antisense oligonucleotide (ASO) that did reduce mHTT in cerebrospinal fluid, but failed its Phase 3 trial in 2021; a subsequent Phase 2 study in a younger population ended the program in 2026 without clinical benefit.
uniQure announced on November 2, 2026 that the FDA accepted for review the Biologics License Application (BLA) for ifezuntirgene inilparvovec, the company's investigational gene therapy for Huntington's disease, granting it Priority Review with a Prescription Drug User Fee Act (PDUFA) target action date of May 1, 2027. If approved, it would be the first disease-modifying treatment for Huntington's disease cleared by any regulatory authority.
Huntington's gene therapy BLA: a non-linear path to review
The BLA for ifezuntirgene inilparvovec, also known as AMT-130, rests on Phase 1/2 data from two studies (NCT04120493; NCT05243017) that the FDA initially rejected as insufficient before reversing course. High-dose treatment slowed disease progression by 75 percent at 36 months on the composite Unified Huntington's Disease Rating Scale (cUHDRS) versus a propensity score-matched external control from the Enroll-HD natural history database (p=0.003). A follow-up analysis in 15 high-dose participants pushed that figure to 80 percent slowing on cUHDRS and 67 percent slowing on Total Functional Capacity (TFC).
At a pre-BLA meeting in late 2025, the FDA reversed earlier guidance, telling uniQure that Phase 1/2 external-control data no longer sufficed for a BLA. After a subsequent Type B meeting, the agency reversed course again in June 2026, accepting that three-year Phase 1/2 data could serve as the primary basis for accelerated approval submission, provided a confirmatory trial was underway. uniQure filed the BLA in September 2026 and simultaneously submitted a Marketing Authorization Application (MAA) with the UK's Medicines and Healthcare products Regulatory Agency (MHRA).
What the 48-month data add to the regulatory picture
Shortly before BLA acceptance, uniQure released 48-month follow-up results that fell outside the submitted dossier. In 12 high-dose participants, TFC progression slowed by 61 percent and cUHDRS by 44 percent, with the cUHDRS result not reaching statistical significance (p=0.144). The company attributed the attenuation to missing data and survivor bias in an updated external-control dataset; a sensitivity analysis using the prior Enroll-HD control returned 53.5 percent slowing on cUHDRS (nominal p=0.041) and 68.3 percent slowing on TFC (nominal p=0.001).
The FDA evaluated the BLA on the three-year dataset. The Advisory Committee meeting the agency is tentatively planning before the PDUFA date will likely scrutinize how these post-submission findings bear on the evidentiary package.
A single miQURE dose silences the huntingtin gene permanently
Ifezuntirgene inilparvovec delivers an artificial microRNA (miRNA) to striatal neurons via an adeno-associated virus serotype 5 (AAV5) vector, using uniQure's proprietary miQURE platform to silence HTT expression from a single administration. Inside target neurons, the miRNA loads into the RNA-induced silencing complex (RISC) and directs sequence-specific cleavage of HTT messenger RNA (mRNA), cutting huntingtin protein production at the transcript level rather than targeting aggregated protein downstream.
Surgeons deliver the therapy through MRI-guided, convection-enhanced stereotactic neurosurgery directly into the caudate and putamen bilaterally. A micro-catheter distributes the AAV5 vector across the striatum using bulk-flow mechanics, exploiting the serotype's neurotropism for high neuronal transduction. In the Phase 1/2 program, CSF neurofilament light chain (NfL), a marker of neuronal injury, fell to 6 percent below baseline at 36 months in 14 evaluated high-dose participants, running counter to the progressive rise seen in untreated disease.
The miQURE miRNA targets both wild-type and mutant HTT transcripts, distinguishing it from allele-selective approaches built to preserve healthy protein. Six key data points from the Phase 1/2 program capture the clinical and safety profile:
- Single administration: MRI-guided, convection-enhanced bilateral intrastriatal neurosurgery; no repeat dosing
- Scale: 51 participants dosed across four cohorts in a US randomized controlled study and a European open-label study
- Efficacy (36 months): 75 to 80 percent slowing of cUHDRS progression in high-dose participants versus propensity-matched Enroll-HD external control (p=0.003 to 0.005)
- Biomarker: CSF NfL 6 percent below baseline at 36 months in 14 evaluated high-dose participants
- Durability: Dose-dependent separation between low-dose and high-dose cohorts persisted at 48 months on both TFC and cUHDRS
- FDA designations: Breakthrough Therapy, Regenerative Medicine Advanced Therapy (RMAT), and Fast Track, the first Huntington's therapy to hold all three simultaneously
Confirmatory trial: 200 participants, TFC primary endpoint at 36 months
Under the FDA's accelerated approval framework, uniQure must run a confirmatory trial to verify clinical benefit. The study enrolls approximately 200 participants in a 2:1 ratio of ifezuntirgene inilparvovec to standard of care, with TFC as the primary endpoint at 36 months. Screening in the United States begins before the end of 2026, with enrollment expected to be underway before the May 2027 PDUFA date.
Ralf Reilmann, MD, PhD, FAAN, Founding Director and CEO of the George-Huntington-Institute in Münster, Germany, served as a Phase 1/2 trial investigator and presented three-year outcomes data at the American Academy of Neurology (AAN) Annual Meeting. The standard-of-care control design reflects a negotiated outcome between company and regulator: earlier FDA communications preferred a sham-surgery arm, raising ethical questions given the invasiveness of bilateral neurosurgical delivery.
Matt Kapusta, CEO of uniQure, framed the FDA acceptance as a generational milestone. "The FDA's acceptance of our BLA for review marks an important milestone for the Huntington's disease community, which has waited generations for a treatment that changes the course of this devastating disease," Kapusta said. "Backed by compelling data from our Phase I/II studies, we believe ifezuntirgene inilparvovec has the potential to become the first disease modifying [sic] treatment for Huntington's disease."
Does a one-time gene therapy outpace repeat-dosing rivals?
Ifezuntirgene inilparvovec's core clinical claim is durability from a single intrastriatal procedure, compared with intrathecal injections every few weeks or daily oral dosing required by competing approaches. Three mechanistic classes are now represented in the late-stage Huntington's pipeline, each targeting huntingtin suppression through a distinct modality and dosing structure:
| Modality | Approach | Dosing |
|---|---|---|
| AAV5 miRNA gene therapy | Non-allele-selective HTT silencing via intrastriatal vector delivery | Single administration |
| Allele-selective ASO | Selective suppression of mutant HTT transcript; wild-type preserved | Repeated intrathecal injection |
| Oral small molecule | HTT pre-mRNA splicing modulation | Once daily |
The clearest clinical precedent for interpreting ifezuntirgene inilparvovec's results is a prior non-allele-selective ASO program that successfully reduced mHTT in cerebrospinal fluid but produced no clinical benefit in Phase 3, with the more frequent dosing schedule worsening outcomes rather than improving them.
The working hypothesis for ifezuntirgene inilparvovec is that permanent gene silencing from a single administration avoids the cumulative tolerability problems linked to repeated intrathecal dosing. The 36-month cUHDRS and TFC results provide the first human evidence that durable huntingtin suppression from one procedure is achievable, and the confirmatory trial will determine whether that suppression yields a statistically robust clinical signal.
A May 2027 decision could end three decades without a disease-modifying Huntington's treatment
Ifezuntirgene inilparvovec enters FDA review holding Breakthrough Therapy, RMAT, and Fast Track designations, with a PDUFA target action date of May 1, 2027 and a tentative Advisory Committee meeting that will subject the three-year BLA dataset and post-submission 48-month data to independent scientific scrutiny. Screening for the confirmatory trial begins before year-end 2026, and a parallel MAA awaits review by the UK's MHRA. If approved, ifezuntirgene inilparvovec would be the first treatment shown to slow Huntington's disease progression, ending a therapeutic drought that has persisted since the disease-causing mutation was identified more than three decades ago.
This article is based on a press release issued by uniQure and was produced under Drug Discovery News' AI Editorial Guidelines.
