Dear ALS/MND Community,
We are writing to inform you that Ionis has completed enrollment of FUSION (NCT04768972), the pivotal Phase 3 clinical trial of our investigational medicine, ulefnersen (ION363). FUSION was designed to evaluate the efficacy of ulefnersen for the potential treatment of amyotrophic lateral sclerosis in carriers of fused in sarcoma mutations (FUS-ALS).1
This milestone is the result of a dedicated global collaboration with the ALS/MND community and investigators at 25 clinical trial sites across 16 countries, which identified and enrolled more than 80 people living with FUS-ALS in this pivotal clinical trial.1
With the trial now fully enrolled, we estimate that it will reach its primary completion date in the second half of 2026, after all participants have completed all study visits associated with the double-blind placebo-controlled phase. 1,2 Ionis and Otsuka will review data following that milestone and update the ALS/MND community as appropriate.
Ionis and Otsuka recognize the considerable and ongoing dedication of individuals living with ALS enrolled in FUSION, as well as their caregivers, and thank them for their contributions to science.
Sincerely,
The Ionis & Otsuka Ulefnersen Team
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How does this milestone impact people enrolled in FUSION?
Individuals enrolled in FUSION will continue to complete all planned study procedures and assessments according to the study protocol. Individuals enrolled in FUSION should continue to direct questions about their participation to their study site.
Can additional people, such as those newly diagnosed with FUS-ALS, enroll in FUSION?
Ionis and Otsuka recognize the devastating nature of a diagnosis of FUS-ALS. However, as the trial has completed enrollment, additional individuals diagnosed with FUS-ALS will not be enrolled. We continue to work closely with all clinical trial sites and participants to complete the trial as quickly as possible and will share the results as appropriate following its completion.
Is there a way to receive ulefnersen outside the clinical trial?
Evaluating the safety and efficacy of ulefnersen in the FUSION trial is essential to establishing whether ulefnersen can help carriers of FUS-ALS. With the trial ongoing, sufficient evidence on the safety and efficacy of ulefnersen is not currently available to support an expanded access or compassionate use program for ulefnersen.
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The European Organization for Professionals and People with ALS (www.als.eu) is a community resource that provides education and support to those affected by ALS/MND.
For more information about Ionis, visit www.ionis.com or email padvocacy@ionis.com.
Abbreviations: ALS, amyotrophic lateral sclerosis; MND, motor neuron disease
References: 1. FUSION: a study to evaluate the efficacy, safety, pharmacokinetics and pharmacodynamics of ION363 in amyotrophic lateral sclerosis participants with fused in sarcoma mutations (FUS-ALS). NCT04768972. Updated August 12, 2025. Accessed August 12, 2025. https://clinicaltrials.gov/study/NCT04768972, 2. ClinicalTrials.gov Glossary of Terms. Updated December 09, 2024. Accessed August 6, 2025. https://clinicaltrials.gov/study-basics/glossary.
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