--- title: An Experimental Drug for a Fast-Moving Genetic ALS Meets Its Goal in a Global Trial description: Ulefnersen, an antisense drug for the rare genetic FUS-ALS, met its main goal in the global Phase 3 FUSION trial. It is not yet approved. author: Darie Nani (Editor-in-Chief) date: 2026-09-23T21:15:12.478Z updated: 2026-09-23T21:15:12.486Z canonical: https://richhealthmagazine.com/article/ulefnersen-fus-als-phase-3-fusion-trial image: https://cdn.nanimediahouse.com/pexels-close-up-of-a-doctor-holding-a-patient-s-hands-symbolizing-t-5206924.jpg categories: Health content_type: News region: Global publication: Rich Health Magazine schema_type: Article --- An experimental drug for one of the cruelest forms of ALS has cleared a global Phase 3 trial, developers Otsuka and Ionis said on September 22, 2026. Ulefnersen, once known as jacifusen, is the first treatment shown to change the course of FUS-ALS, a rare and fast-moving genetic form of the disease that most often strikes young people. Until now, these families have had no treatment made for them. The disease is FUS-ALS, caused by a fault in a gene that carries the instructions for a protein called FUS. It is rare, but it is the most common cause of juvenile ALS, and in young people it often moves quickly. In the Phase 3 trial, ulefnersen showed [a statistically significant improvement over placebo on the study's main measure](https://www.otsuka-us.com/news/otsuka-announces-transformative-phase-3-fusion-results-ulefnersen-bringing-fus-als-community), a combined look at how patients functioned and how long they survived. That primary endpoint pulled together the time to death or permanent ventilation, the time to rescue treatment, and the change in a standard ALS functional score from the start of the study to Day 505. The result reached a p-value of 0.0005, meaning it was very unlikely to be down to chance. Otsuka and Ionis call it the first placebo-controlled study to target the underlying genetic cause of FUS-ALS. Levels of serum neurofilament light chain, a marker in the blood that rises when nerve cells are being damaged, also fell in patients on the drug. Side effects were mostly mild or moderate. ## A Drug Named for the Young Woman Who Set It in Motion Ulefnersen was first called jacifusen, after Jaci Hermstad, a young woman living with FUS-ALS whose advocacy helped launch the research. Hermstad died in 2020. “Today's results happened because of an amazing young woman named Jaci Hermstad, her family and a community that refused to accept that a rare form of ALS was too rare to treat,” said Calaneet Balas, president and CEO of the ALS Association, which helped fund the work. The early science was done at Columbia University, led by Dr. Neil Shneider. When the work ran short of resources, the ALS Association partnered with Project ALS to keep it funded, and later supported an expanded-access program that treated more people with FUS-ALS. The association had backed antisense research in ALS about twenty years ago, before this kind of drug had been tried in any neurodegenerative disease. Among the people treated in the expanded-access program, one participant regained the ability to walk and breathe on her own. Those early results helped lead to the global Phase 3 trial. ## A Second Genetic Form of ALS Is Closer to a Treatment Ulefnersen is an antisense therapy, a drug that lowers production of the FUS protein, the protein that goes wrong in FUS-ALS. It is given by injection into the spinal fluid. It would be the second antisense therapy shown to change the course of a genetic form of ALS, after Qalsody, known generically as tofersen, which treats a different genetic form called SOD1-ALS. Qalsody received FDA accelerated approval in 2023 as the first treatment to target a genetic cause of ALS. The drug is not approved. Otsuka and Ionis say they will discuss the FUSION results with the US Food and Drug Administration and health authorities around the world to seek a faster path to approval. FUSION, registered as NCT04768972, was a global, randomized, double-blind, placebo-controlled study. A single strong trial is a major step toward a treatment, though not the same as one. The ALS Association says it will keep pushing for a fast regulatory review. “We are fighting for families affected by this especially cruel type of ALS,” Balas said, “and we hope today's news provides encouragement.” ## FAQ **Q: How common is FUS-ALS?** FUS-ALS makes up an estimated 0.6% of all ALS cases, but FUS gene changes are far more common in juvenile and pediatric ALS, where they account for an estimated 43 to 52% of cases. It tends to begin at a younger age and to progress quickly. **Q: What has the FDA already done for ulefnersen?** The FDA has granted ulefnersen Fast Track designation for FUS-ALS, and the drug holds Orphan designation for ALS from the US FDA, the European Medicines Agency, and Swissmedic. These designations are meant to speed the development and review of treatments for rare diseases. They are not approvals. **Q: How was the FUSION trial run?** FUSION was a global Phase 1-3 study. In its first part, participants were randomly assigned to receive ulefnersen or a placebo, given by injection into the spinal fluid, over a 72-week period. An open-label extension is ongoing to follow longer-term safety and how well the drug keeps working. **Q: Why does the FUS gene cause this form of ALS?** In FUS-ALS, changes in the FUS gene cause the FUS protein to build up abnormally in nerve cells. Ulefnersen is designed to reduce how much of the protein the body makes.