The US FDA has approved Zanvastro (zilganersen), an antisense oligonucleotide (ASO) targeting glial fibrillary acidic protein (GFAP) mRNA, for the treatment of Alexander disease (AxD) in pediatric and adult patients. Ionis Pharmaceuticals (Nasdaq: IONS) said the approval represents the only disease-modifying therapy available for AxD, an ultra-rare, progressive, and often fatal neurological disorder affecting approximately 1 in 1 to 3 million people worldwide, for which prior management was limited to symptomatic care. The FDA also granted Ionis a Rare Pediatric Disease Priority Review Voucher (PRV) in conjunction with the approval, which arrived 19 days ahead of the original September 22 PDUFA date.

Zanvastro is administered as a 50 mg intrathecal injection every 12 weeks. The intrathecal route enables direct central nervous system delivery, bypassing the blood-brain barrier — the same approach Ionis has applied across its neurology ASO portfolio, including nusinersen (Spinraza) for spinal muscular atrophy, as covered in the context of next-generation intrathecal ASO programs. Zilganersen reduces GFAP protein production via RNA-targeted inhibition of GFAP mRNA, addressing the toxic protein accumulation in astrocytes that drives AxD pathology.

The approval was based on the Phase I-III pivotal study NCT04849741, a global, multicenter, randomized, double-blind, controlled trial enrolling 54 participants aged 1.5 to 53 years across 13 sites in eight countries. In participants aged 5 years and older, Zanvastro 50 mg demonstrated statistically significant stabilization of gait speed versus control at Week 61, as measured by the 10-Meter Walk Test (least square mean difference 33.3%, p=0.041). In patients aged 2 to 4 years, improvement in gross motor function was reported using the Gross Motor Function Measure-88. Patient-, caregiver-, and clinician-reported secondary endpoints consistently favored Zanvastro. Serious treatment-emergent adverse events occurred less frequently in the Zanvastro group than in controls; aseptic meningitis was identified as a labeled warning and precaution.

No pharmacological comparators exist for AxD: prior to this approval, no disease-modifying therapy had been approved for the indication, leaving treatment limited to symptomatic and supportive care. Zanvastro's approval marks Ionis's first independent neurology launch and its second independent product launch in 2026, following the June expansion of Tryngolza (olezarsen) into severe hypertriglyceridemia. For ex-US rights, Ionis entered a license agreement with Italy-based Recordati in June 2026, under which Recordati obtained exclusive development and commercialization rights outside the US for an upfront payment of USD 30 million plus tiered royalties up to the mid-20% range; regulatory submissions in Europe and Japan are expected in 2027.

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