On September 5, Ionis Pharmaceuticals fell 9.43% in after-hours trading, trading at $55.35 per share, with turnover of approximately $2.1 million.

On the news front, the FDA on September 4 officially approved the company's Zanvastro (zilganersen) injection for the treatment of Alexander disease in pediatric and adult patients, ahead of the PDUFA target date of September 22. The pivotal trial met its primary endpoint, with the 50-milligram dose demonstrating statistically significant stabilization of gait speed at week 61 in patients aged five and older. The approval marks a breakthrough for this ultra-rare, progressive, and often fatal neurological disorder. Ionis had previously licensed ex-US rights to Recordati, receiving $30 million upfront along with milestone payments and mid-20% royalties on net sales, while retaining US commercialization rights. Despite the positive regulatory milestone, the stock came under pressure as the approval had been widely anticipated following strong clinical data and priority review designation earlier this year.

Within the Biotechnology sector, Amgen fell 5.08%, Moderna fell 0.38%, Gilead Sciences fell 0.14%, AbbVie fell 0.06%, while Regeneron Pharmaceuticals rose 0.12%.

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