BUZZ-Regenxbio plunges as FDA places hold on Hunter syndrome gene therapy

** Shares of drug developer Regenxbio RGNX.O fall 25% to $8.08 premarket

** The U.S. FDA places a clinical hold on Regenxbio's experimental gene therapy RGX-121 for Hunter syndrome after MRI scans identify small, symptom-free spinal abnormalities in five patients

** Co says all five patients remain clinically stable or show improvement, and doctors believe the findings are likely benign

** Does not expect to resubmit its U.S. approval application for RGX-121 in the near term, co says

** Earlier this year, the FDA had declined to approve RGX-121, citing uncertainty regarding the trial design

** As of last close, stock down 25.6% YTD