(Bloomberg) -- Sarepta Therapeutics Inc. shares soared after US regulators granted a speedy review to an application to expand its gene therapy to older children with Duchenne muscular dystrophy.

The treatment, called Elevidys, received accelerated approval last year to treat 4- and 5-year-olds with the muscle disease. The Food and Drug Administration is expected to decide on the expansion by June 21, the company said Friday in a statement.

Sarepta rose as much as 15% at the New York market open, the most since Jan. 9.

Elevidys was cleared in June via accelerated approval, a regulatory shortcut designed to get drugs for devastating diseases to market quickly, based on preliminary data, before definitive trials are complete. The FDA could do anything from rescinding the current approval, to giving it full approval for a broader age group, to something in between.

The FDA won’t convene another panel of outside advisers to consider the drug, Sarepta said. That’s “a positive sign for expansion and conversion to full approval,” William Blair & Co. analyst Tim Lugo said in a note.

The most likely scenario is that the drug gains full approval for 4- and 5-year-olds, and the agency grants accelerated approval for children 6 and 7 years old, according RBC Capital Markets analyst Brian Abrahams. If that were to take place, US sales of the drug could reach $1 billion annually and Sarepta’s share price could rise to $170, he said in a note. 

In October, the company said a trial of its $3.2 million treatment failed to clearly slow the disease in a yearlong study of young children. But Sarepta said that secondary measures of patients’ movement in the trial were positive, and it planned to file with US regulators for expanded, full approval.

Sarepta has partnered on the drug with Roche Holding AG. Sarepta leads commercialization and manufacturing of the drug in the US, while Roche holds the rights to sell the drug outside the country.

The accelerated approval system can be helpful in situations where patients are desperate to try any treatment at all. But critics say it can result in unproven drugs lingering on the market for years.

(Updates with shares, analyst comment starting in third paragraph.)

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