Huntington's disease is a fatal, inherited neurodegeneration caused by a CAG-repeat expansion in the HTT gene. For years, disease-modifying therapy proved elusive — but the field has just recorded its first genuine breakthrough, alongside hard lessons from earlier huntingtin-lowering programs.
The breakthrough: AMT-130 gene therapy
AMT-130 (uniQure) is a one-time, AAV5-delivered gene therapy carrying an engineered microRNA that lowers huntingtin, administered by MRI-guided stereotactic delivery into the brain. In its pivotal Phase 1/2 program, high-dose AMT-130 became the first therapy ever to show statistically significant slowing of Huntington's progression on accepted clinical measures: at 36 months it slowed decline by 75% on the composite Unified Huntington's Disease Rating Scale (cUHDRS) versus a propensity-matched external control (p=0.003), with a 60% slowing on Total Functional Capacity (p=0.033) and CSF neurofilament remaining below baseline. It was generally well tolerated, with most adverse events tied to the surgical procedure. The therapy holds FDA breakthrough therapy designation.
An important caveat on the regulatory path: although earlier FDA meetings had supported a filing based primarily on Phase 1/2 data against an external control, a 2026 pre-submission meeting signaled that this may not suffice — leaving the timeline to any accelerated approval uncertain. The clinical result is a landmark; the route to market is still being negotiated, and the small sample and external-control design warrant measured interpretation.
Huntingtin-lowering: lessons from ASOs
Tominersen, an intrathecal antisense oligonucleotide, lowered mutant huntingtin in its Phase 3 GENERATION HD1 trial but was halted in 2021 when higher doses were associated with worse outcomes. Rather than abandoning the drug, the sponsor redesigned the approach — lower doses in younger, earlier-stage patients — in GENERATION HD2, which remains ongoing with no new safety concerns and is expected to read out around 2026. Votoplam (PTC518), an oral, brain-penetrant splice modifier that lowers huntingtin, is advancing in PIVOT-HD through a PTC Therapeutics/Novartis collaboration, and newer entrants (SKY-0515, WVE-003, ALN-HTT02, SPK-10001) are moving into trials.
Symptomatic therapy and a program that fell short
Deutetrabenazine and valbenazine, both VMAT2 inhibitors, remain effective and well-established for chorea, with valbenazine's benefit confirmed in the Phase 3 KINECT-HD trial; valbenazine carries a comparatively lower psychiatric burden, though VMAT2 inhibitors still warrant monitoring for depression and suicidality. Pridopidine, a sigma-1 receptor agonist, did not meet the primary endpoint (Total Functional Capacity) in its Phase 3 PROOF-HD trial despite some secondary signals, and its development has faced a regulatory setback.
| Therapy | Class | Result | Status |
|---|---|---|---|
| AMT-130 | AAV gene therapy (HTT-lowering) | 75% slowing on cUHDRS at 36 mo (p=0.003) | Positive pivotal data; breakthrough designation; regulatory path unresolved |
| Tominersen | ASO (HTT-lowering) | HD1 halted (worse at high dose); HD2 redesigned | HD2 ongoing (~2026) |
| Votoplam (PTC518) | Oral splice modifier | HTT lowering in trials | PIVOT-HD / PTC–Novartis |
| Pridopidine | Sigma-1 agonist | PROOF-HD missed primary | Setback |
| Deutetrabenazine / Valbenazine | VMAT2 inhibitors | Significant chorea reduction | Established (symptomatic) |
For the first time, huntingtin-lowering has translated into measurable clinical slowing in patients — a watershed for the field, even as the regulatory and confirmatory work continues.
Further reading: AMT-130 Phase 1/2 topline (uniQure, 2025); GENERATION HD1 (Tabrizi et al., NEJM 2023) and GENERATION HD2 (ongoing); PROOF-HD (pridopidine, 2023); KINECT-HD (Furr Stimming et al., Lancet Neurology 2023); Farag, Tabrizi & Wild HD clinical trials updates (2025).