European regulators have decided to allow Translarna, PTC’s controversial treatment for the deadly genetic rare disease Duchenne muscular dystrophy, to remain on the market on a conditional basis.

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It’s a controversial proposition given that the therapy hasn’t shown significant efficacy in clinical trials. In fact, many analysts expected that the drug wouldn’t be allowed to remain on the market, and the Food and Drug Administration has eschewed its regulatory application in the U.S.

But the EU advisory body recommended that the European Medicines Agency (EMA) allow sales to continue provided that PTC (PTCT) performs larger studies proving Translarna’s effectiveness. (The studies wouldn’t conclude until 2021, giving PTC plenty of time to remain on the market provisionally.)

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Medicines for rare diseases and unmet medical needs have presented a fascinating quandary for regulatory bodies, which must balance empirical judgments on efficacy and safety with more subjective political and, well, emotional considerations.

And Duchenne has become a particularly interesting case study on the matter. Earlier this year, the FDA gave a controversial approval to Sarepta’s (SRPT) Exondys 51, which also treats a form of DMD, following a concerted lobbying campaign by patient advocates despite little evidence of significant efficacy and plenty of controversy within the FDA’s staff.