FDA to reverse Regenxbio rejection of Hunter syndrome gene therapy, WSJ reports

FDA reversal

Regenxbio said the U.S. Food and Drug Administration has agreed to reverse its rejection of Navsunli, the company’s gene therapy for Hunter syndrome, according to reporting published Monday.

The reported shift would reopen a path for one of Regenxbio’s most important rare-disease programs after an earlier setback in February 2026. Regenxbio said it plans to refile the application in the third quarter of 2026 if the agency’s current position holds.

The company also expects a formal meeting with the FDA in July to work through the remaining issues.

Why the case matters

Hunter syndrome is a rare genetic disease that causes irreversible brain damage and cell death and is usually fatal in the mid-teens, according to the reporting.

The condition affects about 2,000 people worldwide, nearly all boys, and roughly 50 children are diagnosed each year in the U.S. That small patient population has made it a test case for how regulators weigh limited clinical evidence in severe rare diseases.

For patients, the stakes are unusually high because there are few current options and the disease is progressive and often fatal at a young age.

What changed

The earlier rejection centered on the absence of a placebo arm and questions about trial eligibility, according to the reporting.

Regenxbio had treated 13 patients and argued that the FDA should rely on longer follow-up from that group instead of requiring a new placebo-controlled trial.

The company said the agency is now willing to consider that longer follow-up approach. If that position stands, Regenxbio could avoid starting a new study that it had said would take years and raise ethical concerns.

That makes the reported reversal more than a procedural adjustment. It potentially changes the evidence standard for a fatal pediatric disease where randomized trials can be difficult to run.

Timeline of the dispute

Regenxbio’s application was rejected in February 2026, setting off an appeal and further discussions with regulators.

The company later met with then-FDA Commissioner Marty Makary in April, according to the reporting.

The latest development came after the FDA also reversed course on another rare-disease gene-therapy filing on June 17, underscoring a broader shift in how the agency is handling some of these programs.

Broader stakes for gene therapy

The case matters beyond Regenxbio because it touches on whether the FDA will accept single-arm rare-disease studies supported by extended follow-up instead of requiring new placebo trials.

That question has been central to other gene-therapy and rare-disease reviews, where patient numbers are small and withholding treatment can be controversial.

Denali Therapeutics’ approval in March 2026 for Avlayah, another Hunter syndrome treatment, also shows that the disease area remains active and commercially significant.

What comes next

The next concrete milestone is the July FDA meeting.

If the agency’s reported position remains in place, Regenxbio said it will submit a new filing in the third quarter of 2026.

Open questions remain about the exact data package, whether the FDA will formally confirm the reported reversal, and how the agency will frame the evidence it wants to see before any approval decision.

Investors have already been watching the program closely because the outcome could determine whether Navsunli gets a second chance after the February rejection.