(Bloomberg) -- A gene therapy from Pfizer Inc. failed to improve motor function for patients with a rare, muscle-destroying disease in a key clinical trial, jeopardizing the future of a once-promising medicine. 

The one-time treatment was not significantly better than placebo in a study enrolling boys with Duchenne muscular dystrophy, Pfizer said Wednesday, missing its primary goal of improving patients’ scores on a test of mobility. The treatment also missed its secondary goals in the trial, Pfizer said.

Shares of Sarepta Therapeutics Inc., maker of a rival gene therapy for Duchenne, rose as much as 12% in after-hours trading. Pfizer shares were little changed. 

Pfizer did not say whether it would continue developing its gene therapy, called fordadistrogene movaparvovec. The company will present data from its failed study at a later medical meeting in hopes to “improve future clinical research and development of treatment options that can improve care” for patients with Duchenne, according to a statement.

The failure is a setback for Pfizer’s pipeline as the company searches for products that might return it to growth. Demand for Pfizer’s blockbuster vaccine and treatment for Covid-19 have dramatically declined, and the company’s share price has fallen by roughly one third in the past year.

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