Regenerxbio’s Hunter syndrome gene therapy (RGX-121, clemidsogene lanparvovec) ran into a new safety roadblock as the FDA placed another clinical hold after masses were detected on the spines of five treated patients. The company said the patients were asymptomatic and that the second hold derailed its plan to refile for FDA approval in the near term, following a similar pause earlier this year. The episode renews scrutiny of AAV gene therapy safety signals involving CNS imaging findings. Investors and competitors will watch whether Regenerxbio can characterize the imaging abnormalities, satisfy FDA data expectations, and restart development without further delays.