By Leroy Leo and Aditya Samal
(Reuters) -The U.S. Food and Drug Administration on Thursday granted accelerated approval to Sarepta Therapeutics' first-of-its-kind gene therapy for Duchenne muscular dystrophy (DMD), an inherited progressive muscle wasting disorder that almost always affects young boys.
The FDA's approval for children aged between 4 and 5 years who can walk comes after several delays as well as questions over the therapy's effectiveness.
Sarepta was initially seeking approval for all DMD patients who can walk, but the company said in May the FDA was likely to clear the drug initially only for just 4- and 5-year-olds.
Its one-time gene replacement therapy, to be sold under brand name Elevidys, could change the way DMD patients are treated. Currently, approved steroids and some therapies for specific genetic mutations only control symptoms and slow disease progression.
In a mid-stage trial, Sarepta's gene therapy was able to produce a mini version of the dystrophin protein needed to help keep muscles intact, but did not improve patient clinical outcomes like their ability to walk and stand.
A late-stage study to confirm the gene therapy's effectiveness is underway and initial data from it is expected by December.
Current options for DMD patients, who rarely survive beyond their thirties, are limited, with treatment consisting mostly of cortocosteroids and four new "exon-skipping" therapies for a smaller group of patients with specific genetic mutations.
The therapies, three of which are from Sarepta, require weekly infusions and work by skipping specific parts of genes called exons with the aim of allowing the body to form shorter forms of the dystrophin protein.
Sarepta is prepared with its infrastructure to support the launch of its therapy, which could take about four months to get to patients even with a limited patient population, CEO Douglas Ingram said ahead of the approval.
DMD affects an estimated one-in-3,500 male births worldwide, according to the National Organization for Rare Disorders.
"We will have a very successful launch and I think we'll expand this label successfully early next year," Sarepta's Ingram said.
A green light for Sarepta's treatment could open the doors for more effective gene therapies, experts and analysts have said. Pfizer is also developing a gene therapy for DMD.
Goldman Sachs analyst Salveen Richter last month estimated that the restrictive age group could mean an 80% reduction in the eligible DMD population that Sarepta was expecting.
A late-stage trial of 126 patients is ongoing, and will be pivotal in expanding the patient population and gaining a traditional approval.
Still, Richter estimates peak global sales of the therapy at $3 billion in 2030, including through Sarepta's partnership with Swiss drugmaker Roche.
Roche acquired the commercial rights to the gene therapy outside the United States under a 2019 deal. Sarepta remains in charge of clinical development, but it splits the costs with Roche.
(Reporting by Aditya Samal, Leroy Leo and Raghav Mahobe in Bengaluru; Editing by Shinjini Ganguli)
