Regenxbio shares fell sharply after investors reacted to guidance that the FDA may require a randomized controlled trial for its DMD gene therapy candidate RGX-202, despite positive pivotal phase 3 data. The stock slide followed reports that, during discussions with the agency, FDA recommended an RCT design to assess RGX-202 in Duchenne muscular dystrophy. Regenxbio has said it plans further dialogue with FDA officials, and it argued that externally controlled trials may be adequate when effect sizes are sufficient. The episode highlights the durability of “accelerated pathway” expectations for gene therapies when trial evidence packages can still be renegotiated. For the category, timing uncertainty can materially affect market entry, reimbursement planning, and competitive positioning.