When one player stumbles in a high-stakes competition, it's often to the glee of the other contenders. In mid-June, Pfizer's (NYSE: PFE) gene-therapy candidate to treat Duchenne muscular dystrophy (DMD) didn't hit the mark in a late-stage clinical trial; it'd be logical to assume that shares of Sarepta Therapeutics, (NASDAQ: SRPT) a biotech focused on developing DMD drugs, would then rise.

But that didn't happen -- at least not until Sarepta got a green light for one of its programs from the Food and Drug Administration (FDA) on June 20, causing its stock to soar by 31%. Let's evaluate the situation and determine whether there's an investable opportunity -- or perhaps a threat to your portfolio, if you're already a shareholder of either business.

DMD is a rare, fatal, degenerative, and predominantly hereditary illness that causes progressively worsening muscle weakness. It's typically diagnosed before patients are 5 years old, and there aren't yet any curative treatments, though there are a few interventions to address some of the symptoms. Beyond that, Sarepta produces several therapies that may be capable of slowing the rate of the disease's progression, and it's currently developing a few more.

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Source Fool.com