FUS-associated amyotrophic lateral sclerosis is rare and hits hard. Most patients see their condition worsen fast. Now, new data from a Phase 3 trial may change that outlook. Ulefnersen, an RNA therapy from Otsuka and Ionis Pharmaceuticals, slowed both functional decline and risk of death at 72 weeks. Placebo did not.
The FUSION trial is the first global, multicenter, randomized, double-blind, placebo-controlled study specifically targeting the underlying genetic cause of FUS-ALS.
Ulefnersen works by binding to FUS pre-messenger RNA. This cuts down production of the FUS protein, including the mutant forms that damage motor neurons. No other approved therapy has targeted the genetic root of FUS-ALS in this way. Otsuka says ulefnersen is given intrathecally. The company secured global rights to develop and sell the drug through an exclusive license with Ionis in 2024, as detailed in the official company press release.
Otsuka is not waiting. The company plans to talk with regulators and has started an early-access program for patients with genetically confirmed FUS-ALS who cannot join clinical trials. For these patients, choices have been almost zero. The Early Access Program is already in place to get ulefnersen to those who qualify outside of ongoing studies.
The ALS Association welcomed the Phase 3 results, highlighting that ulefnersen demonstrated meaningful improvement in the combined function/survival endpoint and maintained a favorable safety profile, representing a major milestone for this ultra-rare ALS subgroup.
No approved therapies exist for FUS-ALS. Ulefnersen now shows clear benefit in a controlled trial. The next steps are regulatory review and possible approval. For patients who have waited with no options, this could be the first real lifeline. The FUSION data set a new standard for targeted RNA therapies in neurodegenerative disease. The ALS community is watching. Otsuka and Ionis are moving toward regulatory submission.
