The US Food and Drug Administration approved Zanvastro (zilganersen) on 3 September 2026 as the first disease-modifying treatment for Alexander disease, Ionis Pharmaceuticals (NASDAQ: IONS) said.
The approval covers both paediatric and adult patients with the ultra-rare, often fatal neurological disorder, and lands more than two weeks ahead of its 22 September regulatory deadline, according to BioSpace.
First treatment for an untreatable disease
Alexander disease is caused by pathogenic variants in the GFAP gene and, until now, had no approved therapy beyond symptom management, Ionis said in its investor release. Zanvastro is designed to directly target the protein buildup that drives the condition, according to NeurologyLive.
A pivotal trial showed walking speed held stable in treated patients, while a control group saw a 33% decline, STAT News reported. Ionis said the drug would reach US patients “in the coming weeks.”
Market reaction falls flat
IONS shares closed at $58.495 as of 4 September, down 0.72% on the day and up just 2.76% over the trailing 20 sessions, despite the regulatory milestone, according to Benzinga.
Trading volume ran at roughly half its 20-day average. FINRA data show the stock’s short-volume ratio had already fallen from 0.752 on 26 August to 0.273 on 3 September, the day of the approval, suggesting bearish positioning had eased well before the announcement broke.
H.C. Wainwright reiterated a Buy rating and a $115 price target on Ionis following the approval, implying nearly 100% upside from the stock’s pre-approval level of $58.13, Investing.com reported. The gap between that target and the market’s muted response underscores how much of the approval may already have been priced in.
A voucher and a licensing partner
The FDA granted Ionis a Rare Pediatric Disease Priority Review Voucher alongside the approval, the company said. Such vouchers can be sold or used to accelerate review of a future drug application, and have fetched tens of millions of dollars in past transactions involving other biotech firms.
Ionis licensed ex-US commercialisation and development rights for zilganersen to Italian specialty pharma group Recordati in June 2026, meaning international sales would flow through that partnership rather than directly through Ionis, Benzinga reported. Zanvastro marks the company’s first wholly independent neurology launch, following its earlier expansion of Tryngolza for severe hypertriglyceridemia the same month, according to BioSpace. Ionis has said it intends to use the same launch infrastructure for other rare neurodegenerative programmes, including one targeting Angelman syndrome.
Financial backdrop
The approval comes as Ionis works through a period of uneven quarterly results. The company reported a net loss of $114.6m in the second quarter of 2026, on revenue of $267.9m, according to its 10-Q filed with the SEC. That followed a first-quarter loss of $92.5m on revenue of $246.1m. Diluted losses per share were 69 cents in the second quarter, against 56 cents in the first.
Ionis swung to a rare quarterly profit of $123.6m in the second quarter of 2025 before returning to losses in subsequent periods, filings show, underscoring how dependent its earnings remain on licensing payments and one-off items rather than steady product revenue. Four insiders, including chief scientific officer Frank Bennett and general counsel Patrick R. O’Neil, filed Form 4 disclosures with the SEC on 3 September, the same day as the approval, though the filings do not specify transaction values.
Treasury markets were broadly steady around the announcement, with the 10-year yield at 4.79% and the two-year at 4.39% as of early September, Federal Reserve data show, offering no particular tailwind or headwind to biotech valuations at the time of the approval.
Attention now turns to how quickly Ionis can convert the approval into billed prescriptions once Zanvastro reaches pharmacies, and whether the priority review voucher becomes a further catalyst if the company opts to sell it.
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