FDA Reverses Rejection of Regenxbio's Rare Disease Gene Therapy

The U.S. FDA is reversing its February rejection of Regenxbio's gene therapy, Navsunli, for the rare genetic disorder Hunter syndrome. The agency now deems existing data sufficient for an accelerated approval filing, a turnaround from its decision citing trial design uncertainty. This is part of a broader FDA policy shift, with similar recent reversals for other companies, following leadership changes and meetings with advocacy groups.

FDA reversal decision

• ▪The U.S. FDA has indicated it will reverse its February 2026 rejection of Regenxbio's gene therapy, Navsunli
• ▪Shares of Rockville, Maryland-based Regenxbio rose 10% in premarket trading on June 22, 2026, following the news
• ▪The FDA now considers existing data sufficient to support an accelerated approval application for Navsunli
• ▪The FDA's initial rejection of Navsunli was due to uncertainty over the trial's design

Hunter syndrome gene therapy

• ▪Navsunli is a gene therapy for Hunter syndrome, also known as mucopolysaccharidosis type II (MPS II)
• ▪An existing enzyme-replacement therapy for MPS II cannot enter the brain, leading to progressive cognitive decline in children with the neurological form of the disease
• ▪Hunter syndrome is a rare genetic disorder where the body cannot break down certain sugar molecules, affecting physical and cognitive development

Broader FDA policy shift

• ▪The decision reflects a broader FDA shift on rare-disease therapies and an effort to mend ties with the sector
• ▪The turnaround is one of several apparent FDA reversals in the past two months after Trump administration-era leaders resigned or were fired
• ▪Acting FDA Commissioner Kyle Diamantas met with advocacy groups in June 2026, prior to the reversal

Resubmission timeline

• ▪The FDA indicated it would not require Regenxbio to enroll additional patients or conduct new studies, including a previously requested placebo-controlled trial
• ▪Regenxbio plans to seek a formal meeting with the FDA in July 2026 and aims to resubmit its application in the third quarter of 2026

Similar recent reversals

• ▪In May 2026, Replimune planned to seek approval for its experimental skin cancer drug for a third time after reaching an agreement with the FDA
• ▪In June 2026, the FDA also reversed course on uniQure's gene therapy for Huntington's disease, clearing it for an accelerated approval filing