FDA has placed Regenxbio’s Hunter syndrome gene therapy program under another clinical hold after MRI findings involving asymptomatic spine changes, derailing the company’s plan to refile for approval. Regenxbio linked the hold to spine MRI results and said it no longer expects to file in the near term. Separately, Regenxbio disclosed that investigators detected masses on the spines of five patients who received its Hunter syndrome treatment—marking the program’s second clinical hold this year. The company said the patients did not have symptoms related to the masses. The latest pause follows an earlier signal tied to a related AAV gene therapy case, underscoring heightened scrutiny of AAV-associated safety signals. For investors and clinicians, the holds extend uncertainty around the timing and feasibility of regulatory re-engagement for MPS II.