Regenxbio disclosed that it no longer expects to file for FDA approval of its Hunter syndrome gene therapy RGX-121 in the near future after the program received a second clinical hold this year. The hold follows asymptomatic spine MRI findings in enrolled patients, interrupting the company’s planned resubmission path. STAT+ reported the FDA pause details, emphasizing that the masses were detected without linked symptoms. The decision creates additional uncertainty for the timeline of the company’s registrational efforts and raises questions about how AAV gene therapy programs are managing and interpreting imaging signals during late-stage development. For the broader gene therapy sector, the case highlights the operational impact of repeated clinical holds: trial continuity, patient management strategies, regulatory resubmission readiness, and costs associated with additional monitoring and analysis. The situation also reinforces the importance of early safety signal detection and protocol design around imaging endpoints for spinal outcomes, particularly for neurologically targeted AAV platforms.