PTC Therapeutics (PTCT -0.32%) shares soared recently after the EU issued a preliminary approval for the company's Duchenne muscular dystrophy (DMD) drug, Translarna. This caught the market by surprise, which explains the 59% gains over the course of 3 days. Is their still upside in Translarna, or would investors be better served taking a long look at one of its competitors?

The other two stocks attmepting to treat DMD are using a different approach from PTC and have had mixed results. Prosensa's (Nasdaq: RNA) drug failed a phase 3 trial and its big pharma partner walked away, while Sarepta (Nasdaq: SRPT) has promising enough mid-stage results that it is pushing for an accelerated approval from the FDA.

In this episode of The Motley Fool's health-care show Market Checkup, analysts David Williamson and Michael Douglass talk about Translarna's surprising approval and what it means for investors in PTC Therapeutics, Sarepta, and Prosensa.