Liver Toxicities Force Pause on Two Dose Groups of UniQure’s Mid-Stage Fabry Study

Why It Matters

The pause underscores safety hurdles for high‑dose AAV gene therapies, potentially delaying timelines and affecting investor confidence, while the robust enzyme expression keeps AMT‑191’s therapeutic promise for Fabry disease alive.

Key Takeaways

• Mid/high-dose groups paused for grade 3 liver elevations
• Low-dose cohort showed no serious adverse events
• Enzyme activity rose up to 223.7‑fold at highest dose
• Six of eleven patients stopped enzyme replacement therapy
• Corticosteroids resolved liver toxicity in affected patients

Pulse Analysis

Fabry disease, a rare lysosomal storage disorder, has long relied on lifelong enzyme replacement therapy, which carries infusion burdens and variable efficacy. Recent advances in adeno‑associated virus (AAV) vectors promise a one‑time gene‑editing solution by delivering functional copies of the GLA gene to restore alpha‑galactosidase A activity. Within this competitive landscape, UniQure’s AMT‑191 aims to achieve durable enzyme expression, positioning the company to capture a sizable share of the growing rare‑disease gene‑therapy market.

The Phase 1/2a trial’s interim data reveal a classic dose‑response curve: higher vector loads produce markedly greater enzyme activity, reaching up to 223.7‑fold above baseline, and enable a majority of participants to cease conventional enzyme replacement. However, the emergence of grade 3 liver enzyme elevations in the mid‑ and high‑dose cohorts triggered a protocol‑mandated pause, highlighting the narrow therapeutic window of AAV‑based products. Such hepatotoxicity, often linked to innate immune activation, forces developers to balance potency with safety, prompting dose‑optimization studies and proactive corticosteroid regimens to mitigate liver stress.

Looking ahead, UniQure must generate comprehensive safety and efficacy datasets to satisfy regulators and reassure investors. If the low‑dose arm proceeds without further adverse events, the company could pursue a differentiated dosing strategy that maximizes benefit while minimizing hepatic risk. Success would not only validate AMT‑191 as a viable one‑time treatment for Fabry patients but also set a precedent for dosing frameworks across the broader gene‑therapy pipeline, influencing future approvals and market dynamics.