With the details from the DEMAND-III study, the full extent of the failure of Prosensa’s exon-skipping drug drisapersen to arrest progression of Duchenne Muscular Dystrophy (DMD) has become clear.

There are few grounds for optimism among the plethora of secondary end-points, no trends, not even a statistically significant post hoc sub-group analysis.  Only pages and pages of convincingly negative data.

While its obviously a relief that concerns about liver toxicities proved unfounded – the treatment was very safe – the safety profile is unlikely to be much consolation for such a convincing lack of efficacy.

But clear-cut as the data is, it leaves one very important question entirely unanswered: was the failure due to insufficient dystrophin production, or – more worryingly – because successfully elevating dystrophin is much less effective than has been assumed?

There are also lessons to be learned beyond DMD: the infinite subtlety of biology means that no phase 3 study is a “slam dunk” – failure lurks round every corner, even in the most unexpected of places.  Public market investors, in particular, can pump up asset valuations on an over-optimistic assessment of early clinical data (as the recent Intercept episode illustrates).  The chastening experience at Prosensa should serve as a warning that translating promise and potential into regulatory approval and sales is often more difficult than it first appears.

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