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What: Ionis Pharmaceuticals (NASDAQ:IONS) is up 37% at 11:35 a.m. EDT after announcing positive phase 3 trial results for nusinersen in infants with spinal muscular atrophy. The results convinced partner Biogen (NASDAQ:BIIB) to exercise its option to license nusinersen, triggering a $75 million payment to Ionis Pharmaceuticals.

So what: No actual details were presented in the press release or accompanying conference call because this was an interim analysis, and the companies are holding the data for an upcoming medical meeting.

Biogen and Ionis Pharmaceuticals noted that nusinersen met its primary endpoint of achieving motor milestones compared to the control group. With it clear that the drug is working, the clinical trial was stopped early to allow the infants receiving placebo to transition to nusinersen.

Now what: Biogen plans to file marketing applications with regulators in the U.S. and EU by the end of the year, with more countries to follow. Given the life-threatening nature of the disease and lack of treatment options, it seems likely regulators will give nusinersen an accelerated review, potentially putting the drug on the market this time next year, if not sooner.

In addition to infant-onset spinal muscular atrophy, Ionis Pharmaceuticals and Biogen are also testing nusinersen in patients with later-onset spinal muscular atrophy and pre-symptomatic infants. Those clinical trials will continue until they have enough data to get approved for those populations.

Brian Orelli has no position in any stocks mentioned. The Motley Fool owns shares of and recommends Biogen and Ionis Pharmaceuticals. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.