REGENXBIO Pauses RGX-121 Development After MRI Findings

The clinical hold stems from an expanded MRI monitoring program that identified small nodules or cystic masses in the spines of five patients who received RGX-121 between three and six years ago. While investigators categorized these findings as nonserious and potentially benign, REGENXBIO stated that further data analysis and long-term follow-up are required to evaluate the therapy's benefit-risk profile. All five affected participants continue to show stable or improved neurocognitive and neurobehavioral health, and no similar abnormalities were observed in brain scans.

Because spinal imaging is not standard practice for MPS II, the underlying prevalence of these findings remains unclear. Roberto Giugliani, a professor at UFRGS in Brazil, suggested the masses might be inherent to the progression of Hunter Syndrome rather than a direct result of the gene therapy. REGENXBIO CEO Curran Simpson emphasized that the company remains focused on its other pipeline candidates, including a Duchenne muscular dystrophy therapy, as it works with the FDA to determine the next steps for the RGX-121 program.