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

Regenxbio said the U.S. Food and Drug Administration has agreed to reverse its earlier rejection of Navsunli, a gene therapy for Hunter syndrome, according to a Wall Street Journal report published Monday.

The reported shift restores a regulatory path that had been blocked since February 2025 and could move the rare-disease treatment back toward review after months of uncertainty.

The company said it now expects to refile the application in the third quarter of 2026 after a meeting with regulators in July. Regenxbio also said the FDA indicated the application could be reviewed in as little as two months.

What changed

The reported turnaround is important because it removes the need for Regenxbio to mount a new placebo-controlled trial, a major hurdle for an ultra-rare disease program.

Instead, the agency is expected to look for longer follow-up data from the original study cohort, according to the Journal.

That matters in Hunter syndrome, a rare and fatal genetic disease that causes progressive brain damage and usually leads to death in the mid-teens. Large placebo-controlled studies are difficult to run in such small patient populations.

The regulatory path

Regenxbio’s earlier application was rejected in February 2025, with the company saying the agency’s concerns centered on the trial design and the evidence package.

The original study included 13 treated subjects and no placebo arm, according to the Journal.

The reported FDA reversal does not mean Navsunli is approved. Regenxbio still has to submit the refiling, and regulators could still request additional information before any formal review begins.

The FDA declined to comment, the Journal said.

Why it matters

Navsunli is part of a broader debate over how regulators should evaluate one-time gene therapies for very small patient groups, especially when standard trial designs are hard to execute.

A reversal on the filing decision could be read as a sign of greater flexibility for rare-disease programs, particularly those that rely on limited clinical data but target serious conditions with few treatment options.

For Regenxbio, the immediate commercial and scientific question is whether the company can convert the reported regulatory shift into an accepted filing and then keep the review on the short timeline it described.

What comes next

The next near-term milestone is the July meeting with regulators, followed by the planned third-quarter refiling.

Investors and patients will then be watching for formal filing acceptance, any added data requests and whether the review window really stays close to two months.

The broader question is whether other rare-disease gene therapy programs can benefit from the same approach if regulators are willing to revisit earlier rejection decisions.

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