Ionis Pharmaceuticals has received approval from the US Food and Drug Administration (FDA) for Zanvastro (zilganersen) to treat paediatric and adult patients with Alexander Disease (AxD), an ultra-rare and progressive neurological disorder.

Zanvastro is the first and only disease-modifying treatment approved for AxD, which affects an estimated one in 1-3 million people worldwide. The disease is caused by mutations in the GFAP gene, resulting in toxic overproduction and accumulation of Glial Fibrillary Acidic Protein (GFAP) in astrocytes.

An RNA-targeted medicine, Zanvastro is designed to reduce GFAP production and address the underlying biology of AxD rather than only managing its symptoms. The 50 mg dose is administered quarterly through an intrathecal injection.

The FDA approval was supported by results from a pivotal clinical study. In patients aged five years and older, Zanvastro 50 mg achieved a statistically significant and clinically meaningful stabilisation of gait speed, measured using the 10-Meter Walk Test (10MWT), compared with control at week 61. In children aged two to four years, the treatment also demonstrated improvement in gross motor function measured using the Gross Motor Function Measure-88 (GMFM-88).

Patient-, caregiver- and clinician-reported outcomes consistently favoured Zanvastro. The treatment demonstrated a favourable safety and tolerability profile, with most adverse events reported as mild or moderate, while serious treatment-emergent adverse events occurred less frequently than in the control group.

Following the approval, Ionis also received a Rare Pediatric Disease Priority Review Voucher (PRV) from the FDA. The company plans to make Zanvastro available in the US in the coming weeks and will provide patient support through its Ionis Every Step programme.

In June 2026, Ionis entered into an agreement with Recordati granting the company exclusive rights to develop and commercialise zilganersen outside the US. Regulatory submissions in Europe and Japan are expected in 2027.