Biogen said its investigational gene therapy for a rare retinal disease failed to meet expectations in a phase 3 clinical trial.

The company is studying timrepigene emparvovec as a potential treatment of choroideremia, an inherited retinal disorder that causes progressive vision loss and ultimately blindness.

But the trial fell short of the primary endpoint of at least a 15-letter improvement in corrected vision after 12 months and failed to demonstrate efficacy for secondary endpoints.