The Food and Drug Administration has started the first regulatory review of a gene therapy for Duchenne muscular dystrophy, the treatment’s developer, Sarepta Therapeutics, announced on Monday.

In a statement, Sarepta said the agency has accepted its application for an “accelerated” approval of the medicine, known as SRP-9001, and will make a decision by May 29. The regulator’s choice would be based on a mixed package of clinical results and come months before Sarepta has data from a definitive, placebo-controlled Phase 3 study. Sarepta believes that trial could serve as a “confirmatory” study that, if positive, would help convert an accelerated nod into a full approval.

Should the FDA approve SRP-9001, Sarepta would bring to market the first gene therapy for Duchenne, a progressive neuromuscular disease with few available treatments. Sarepta’s drug is the furthest along among a few similar, experimental medicines that are meant to slow the disease’s march with a single infusion. The company has proven the treatment can boost the production of a form of the protein dystrophin that’s missing in Duchenne patients, but not that it can change the disease’s trajectory. Phase 3 results are expected by the end of 2023.

The fact that the FDA is reviewing Sarepta’s treatment before those results arrive suggests regulators have a “high interest” in approving the drug and could be open to leaving it on the market even if the study has a statistical “near-miss,” Brian Abrahams, an analyst at RBC Capital Markets, wrote in a note on Monday.

The decision “highlights the continuing permissiveness of the FDA in rare diseases with significant unmet needs” such as Duchenne, he wrote. “We believe it would be difficult to justify withdrawing a [Duchenne] drug from the market if there are any positive [Phase 3] trends.”

An earlier, placebo-controlled Phase 2 study failed to show a benefit for patients versus a placebo, a finding that set back Sarepta’s plan to seek approval by more than a year. The mixed results could lead the FDA to convene a panel of outside experts to review the data.

According to Abrahams, Sarepta expects such a meeting, during which outside experts could seek to delay the drug’s arrival until the Phase 3 trial produces results.

An approval by May 29, though, could put Sarepta months or even more than a year ahead of Pfizer, its main rival. Pfizer’s path to market was delayed by safety concerns in clinical testing. A Phase 3 trial could read out in 2023, however. Assuming positive results, Pfizer expects to seek approval by the end of next year.

Sarepta shares climbed about 4% in early trading on Monday.