Newsroom · ALS (Lou Gehrig's disease) · October 5, 2026

Ulefnersen Wins a Phase 3 Trial in FUS-ALS: What the Results Mean

In short: On September 22, 2026, Otsuka and Ionis announced that ulefnersen met the main goal of its Phase 3 FUSION trial in FUS-ALS, an inherited form of ALS. It is the first successful trial in this form of the disease. ALS still has no cure, and the results have not yet been published in a journal.

What was announced

Otsuka Pharmaceutical and Ionis Pharmaceuticals reported that ulefnersen showed a statistically significant benefit over placebo in the Phase 3 FUSION trial (P = .0005). The main measure combined three things: time to death or permanent ventilation, time to rescue treatment, and change on the ALSFRS-R scale, a standard questionnaire that tracks everyday function.

The randomized, double-blind part of the trial lasted 72 weeks and was followed by an open-label extension, in which everyone can receive the drug.

What FUS-ALS is

FUS-ALS is a genetic form of amyotrophic lateral sclerosis (ALS) caused by changes in the FUS gene. Ulefnersen belongs to a class of drugs called antisense medicines, which are designed to lower the production of a harmful protein. Tofersen (Qalsody), which is FDA approved for SOD1-ALS, uses the same general approach for a different gene.

What else was reported

Secondary results were favorable, including lower blood levels of neurofilament light chain, a marker of nerve-cell damage, and better combined time-to-event outcomes.
Most adverse events were mild or moderate, and the companies describe the safety profile as favorable.

What happens next

The companies say they will review the results with the FDA and discuss faster regulatory routes with health authorities. They also plan to present detailed results at a medical meeting and submit them for peer-reviewed publication. Until that happens, the numbers come from a company announcement and have not been independently reviewed.

Why it matters for people with ALS

Only a small share of people with ALS have a known inherited cause, so this result applies to a limited group. It is still significant for the field: it is the first successful trial in FUS-ALS, and it adds support for the idea that treating the genetic cause of a form of ALS can work. Researchers are testing similar approaches for other ALS genes. Treatments for the most common, non-inherited forms of ALS remain a separate and unsolved challenge.

Frequently asked questions

Is there a cure for ALS?

No. ALS has no cure today. Ulefnersen is an investigational treatment for one genetic form, FUS-ALS, and has not been approved by the FDA.

Can people with FUS-ALS get ulefnersen now?

It is not approved. The companies say they are discussing next steps with regulators and the trial's open-label extension continues. People with FUS-ALS should ask their neurologist about genetic testing and about trials or access programs.

What does p = 0.0005 mean?

It means that a difference this large would be very unlikely to appear by chance if the drug had no effect. It does not say how large the benefit is for an individual person.

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Sources

Ulefnersen meets primary end point in Phase 3 FUSION trial in FUS-ALS. NeurologyLive, September 2026