Progress for AxD Families:
First potential disease-modifying therapy advances toward FDA review.
Drug Development
Ionis Pharmaceuticals, Inc. is a leader in RNA-targeted therapeutics and previously developed a drug to successfully treat spinal muscular atrophy (SMA). Their investigational therapy for Alexander Disease, zilganersen (ION373), uses the same intrathecal delivery method.
In September 2025, Ionis announced positive Phase 3 trial results, showing that zilganersen demonstrated statistically significant and clinically meaningful stabilization of walking ability, along with favorable safety and tolerability. This marks the first time an investigational medicine has shown potential disease-modifying impact in Alexander Disease.
The European Medicines Agency (EMA) has granted orphan drug designation to ION373, providing regulatory and financial incentives to support the development of therapies for rare, life-threatening, or chronically debilitating conditions with no satisfactory treatment options. Upon approval, drugs with orphan designation receive 10 years of market exclusivity in the EU.
Understanding the FDA Process
During the recent Ionis Community Webinar (October 3, 2025), two helpful FDA resources were shared to guide families and advocates in understanding how new therapies progress from research to real-world access. Shared by Ionis, these trusted resources help our community stay informed and empowered through education.
The FDA’s Role in Regulating and Approving Drugs - Learn how the FDA evaluates and approves treatments to ensure safety and effectiveness.
Expanded Access: Information for Patients - Explore how patients may access investigational therapies outside of clinical trials.
Ionis Announces Positive Topline Pivotal Results for Alexander Disease
September 22, 2025
Ionis is excited to announce positive topline results from our pivotal study of zilganersen, an investigational RNA-targeted medicine in development for the treatment of Alexander Disease (AxD), a rare and progressive neurological condition.
Zilganersen granted U.S. FDA Fast Track designation for people living with Alexander disease
October 1, 2024
Zilganersen is the first investigational medicine in clinical development for adults and children living with Alexander disease, an ultra-rare neurological condition
Ionis completes enrollment in pivotal trial evaluating zilganersen in people living with Alexander disease
July 18, 2024
Zilganersen is the first investigational medicine in clinical development for people with Alexander disease, a rare, life-threatening neurological condition
Ionis initiates pivotal clinical study of novel antisense medicine to treat patients with Alexander disease
April 20, 2021
Innovative therapy targeting the root cause of the disease has received orphan drug designation by the U.S. FDA and European Medicines Agency- ION373 is one of Ionis' wholly owned rare disease medicines the company plans to commercialize