FDA places clinical hold on Regenxbio’s RGX-121 gene therapy after spine MRI findings, delaying refiling plans

The U.S. Food and Drug Administration has issued a clinical hold on Regenxbio’s gene therapy candidate RGX-121 after routine MRI scans revealed asymptomatic changes in the spines of trial participants.

The hold follows a February rejection of Regenxbio’s earlier request for approval of RGX-121 for Hunter syndrome, in which the agency asked for additional patients and an untreated control arm. Those requirements were later dropped and the company prepared to refile.

Expanded safety monitoring identified the spine findings, leading the FDA to pause the study and push back any near‑term filing. Regenxbio now says it does not expect to submit a new application in the upcoming quarter.

The regulator had also placed a hold on a related therapy, RGX-111 for MPS I, earlier this year after a central nervous system tumor was observed, underscoring heightened scrutiny of the platform.