FDA paused trials of Regenxbio’s AAV gene therapy for Hunter syndrome again after additional spine MRI findings raised new safety questions, according to statements reported by STAT+ and the company. The hold follows earlier regulatory action tied to a separate AAV-linked brain tumor case in a similar program built for MPS type I. Regenxbio said five treated patients had small masses on spinal MRI but reported no related symptoms. The latest pause derailed the company’s plans to refile for RGX-121 approval, highlighting how MRI-based signals and long-term tumor surveillance continue to shape the path for AAV platforms in pediatric CNS indications. The development matters for the gene-therapy pipeline because it reinforces the scrutiny around insertion-independent AAV risks, including how sponsors interpret imaging findings and communicate evolving risk management to regulators.