Ionis Pharmaceuticals announced that the US Food and Drug Administration (FDA) has accepted for Priority Review the New Drug Application (NDA) for zilganersen, an investigational RNA-targeted medicine for Alexander disease (AxD), a rare, progressive and often fatal neurological condition.

The FDA has set a Prescription Drug User Fee Act (PDUFA) target action date of 22^nd September, 2026.

"Alexander disease is a devastating condition, commonly resulting in progressive motor and cognitive dysfunction, loss of independence, and is often fatal. There are no approved disease-modifying treatments, underscoring the significant unmet need in this community. Priority Review designation underscores the urgent need for treatment options and will enable us to bring zilganersen to patients as quickly as possible. If approved, zilganersen will be the first and only treatment for Alexander disease, marking a breakthrough for patients. It would also mark Ionis’ first independent commercial launch in neurology, an important milestone that strengthens our neurology franchise and supports our goal to deliver a steady cadence of transformational medicines to people with serious diseases,” said Brett Monia, PhD, Chief Executive Officer (CEO), Ionis.

The NDA and Priority Review designation were based on results from the pivotal study of zilganersen in children and adults living with AxD. In the study, zilganersen 50 mg demonstrated statistically significant and clinically meaningful stabilisation on the primary endpoint of gait speed as assessed by the 10-Meter Walk Test (10MWT) compared to control at week 61 (least square mean difference 33.3 percent, p=0.0412) with favourable safety and tolerability. Results across key secondary and exploratory endpoints evaluating adaptive function, communication, GI symptoms, sleep and seizures also consistently favoured zilganersen. New, additional data from the pivotal study will be presented at the 2026 American Academy of Neurology (AAN) annual meeting in Chicago, IL.