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What: Shares of Isis Pharmaceuticals (NASDAQ: ISIS), a developer of antisense drugs across a variety of diseases and disorders, jumped as much as 16% after the company reported positive early stage add-on results for ISIS-SMNrx for the treatment of spinal muscular atrophy (SMA) in children.

So what: According to an Isis press release, children with SMA who received the two highest doses of ISIS-SMNrx (6 mg and 9 mg) continued to show improvement in muscle function tests even after 14 months of a single injection of the drug. Specifically, most children in the 9 mg cohort demonstrated continuing improvement, with no children in the group showing performance declines. Isis also noted that it plans to report data from its ongoing early and mid-stage studies on type 1, 2, and 3 SMA later this year or early next year, and to begin phase 3 trials in early 2014 (assuming everything goes well in early and mid-stage studies).

Now what: Chalk up yet another positive study for Isis, which I've highlighted relentlessly over the past few months for its pipeline diversity (31 clinical and preclinical stage compounds) and 12 separate partnerships over a variety of diseases and disorders. I'd definitely say shareholders deserve to be excited about the enormity of these early stage results in treating childhood SMA, but I'd also keep in mind that we're still a bit away from having concrete mid-stage data and would reserve judgment on ISIS-SMNrx until that time. I would, though, definitely recommend adding Isis to your Watchlist.

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Fool contributor Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, track every pick he makes under the screen name TrackUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong.

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