The French pharma Servier said Tuesday that an experimental drug it purchased in June for $1.55 billion in cash, plus about $1 billion more in potential milestones, failed to slow a rare form of muscular dystrophy in a long placebo-controlled trial.

It’s a surprising setback for both Servier and the patients with Becker muscular dystrophy, who currently have no approved treatments. The drug, called sevasemten and originally developed by Edgewise Therapeutics, had previously shown promising results in a smaller, randomized study.

“The results of the pivotal GRAND CANYON study are not aligned with certain findings observed in prior clinical studies,” Servier said in a statement, using the company’s name for the Phase 3 trial. “Servier is conducting a comprehensive analysis of the GRAND CANYON study dataset, together with relevant prior clinical data, to better understand and further characterize the study findings.”