FDA again paused trials for Regenxbio’s Hunter syndrome gene therapy after safety findings tied to spine MRI abnormalities in five treated patients, according to the company’s disclosure and STAT+ reporting. The FDA’s action blocks Regenxbio’s near-term plan to refile for approval of RGX-121 (clemidsogene lanparvovec). The latest clinical hold follows an earlier stop ordered this year, compounding scrutiny of AAV-based spine-administered gene therapies. Regenxbio said the patients were asymptomatic despite the imaging masses detected, but the agency is requiring additional review before further enrollment or regulatory progress. Separately, reporting indicates the program’s resubmission plans have been derailed by the FDA’s hold over spine MRI findings, leaving uncertainty around timing for any future BLA submission. For the broader field, the case underscores how spinal imaging findings can trigger regulatory pauses even absent clear clinical symptoms.