This is promising but needs publication and expert review.
Here's the actual company statement from today:
https://uniqure.gcs-web.com/news-releases/news-release-details/uniqure-announces-positive-topline-results-pivotal-phase-iii
https://www.cgtlive.com/view/huntington-disease-gene-therapy-nets-rmat-designation
The 2023 study is said to have 39 patients (BBC and their recent statement reports 29). The reported findings may be significant but seem small (e.g., low dose: 0.39 of 14.1 points). Earlier they reported composites from the Unified HD Rating Scale, which has the usual caveats for the behavioral and functional sub-measures (vs. the more reliable motor and cognitive). Today's statement instead focuses on the more objective measures instead of the composite.
Earlier, high-dose responders reportedly didn't just stabilize but got better -- unclear how. The more recent findings report that the disability still progressed, but slowed relative to "propensity-matched" controls. (Note 4 of 10 controls opted to join the trial after 12 months.)
Both mention improvement in NfL (neurofilament light chains), which is an objective but nonspecific (and highly variable) measure of the degree of neuronal decomposition. The statement quantifies this at ~8% -- unclear if this level is convincing.
For such an invasive treatment for a slowly progressing, relatively rare disease, they're probably gathering and publishing data as fast as possible. The short-term results seem good, and it will be good to see long-term results over time.
It's possible some effect seen is due e.g., to immune adjuvants or something else during the therapy, and I would want experts to review the propensity matching.
I would be concerned that the micro-RNA produced either also binds with epitopes from other messenger RNA or induces some immune response. Remember, there's no reversal agent or half-life elimination for such genetic treatments.
So: room for hope but also for caution.