The U.S. Food and Drug Administration placed clinical holds on Regenxbio’s gene‑therapy programs after a pediatric trial participant was diagnosed with a brain tumor. Regenxbio confirmed the holds and said the company is working with regulators as agencies investigate whether adeno‑associated virus (AAV) delivery or vector integration contributed to the finding. The decision came days before an expected regulatory action on a separate Regenxbio filing and sent investor risk signals across AAV gene therapy developers. Regulators flagged a safety signal tied to a single case; Regenxbio said it will provide additional data to the FDA and pause enrollment where required. A clinical hold suspends dosing while the agency reviews unblinded safety data and risk‑mitigating plans. The move highlights intensified FDA scrutiny of integration and oncogenic risk in in‑vivo gene therapy programs and may prompt sponsors to broaden long‑term surveillance and vector biodistribution studies.