To date, over 900 Duchenne patients have been treated with delandistrogene moxeparvovec. "The signal for ALF is exceptionally rare and has only emerged in the non-ambulatory patients," Sarepta's CEO Doug Ingram said on the Monday conference call.

Shares of Sarepta Therapeutics have plunged again after the drugmaker reported a second death in connection with its gene therapy for muscular dystrophy.

Sarepta Therapeutics said a second patient had died after receiving its $3.2 million gene therapy to treat Duchenne muscular dystrophy.