A promising new drug for a rare, inherited form of ALS just passed a critical test. Otsuka Pharmaceutical and Ionis Pharmaceuticals announced that their experimental drug, ulefnersen, met the primary endpoint of a late-stage clinical trial in patients with FUS-ALS — a genetic subtype of amyotrophic lateral sclerosis caused by a mutation that leads to toxic buildup of the FUS protein, progressively destroying the nerve cells that control movement, speech, swallowing, and breathing.

The drug, designed to reduce production of the harmful FUS protein, outperformed placebo on both function and survival. It also reduced biomarkers of nerve cell damage and slowed disease progression, with most side effects being mild or moderate. Otsuka and Ionis are now planning to engage the US FDA and other global regulators to explore accelerated approval pathways.

Key Takeaways:

• FUS-ALS currently has no approved treatments specifically targeting its genetic cause
• Ulefnersen reduced nerve damage markers and delayed disease progression in addition to improving function and survival
• Otsuka has launched a global early access program for eligible FUS-ALS patients who cannot enroll in clinical trials

Why it matters: FUS-ALS is a devastating, rapidly progressing disease that leaves patients unable to move, speak, or breathe on their own — and until now, no targeted therapy existed. A successful late-stage trial brings ulefnersen one step closer to becoming the first approved treatment for this genetic form of ALS, offering real hope to patients and families with few options.