The clinical disappointment centers on the treatment's inability to provide a statistically significant benefit for patients suffering from the fatal, protein-buildup condition. Despite the setback, Ionis CEO Brett Monia suggested the data could still inform future research into the disease, even as the company grapples with the immediate market fallout.

Ionis developed the drug in partnership with AstraZeneca, which also saw its own shares slide 8.2% to $173.85 before the opening bell. While the study failed its primary goal, the company reported that eplontersen remained well tolerated by participants, maintaining a safety profile consistent with earlier testing phases.