REGENXBIO Inc. (Nasdaq: RGNX), a leading clinical-stage biotechnology company seeking to improve lives through the curative potential of gene therapy based on its proprietary NAV® Technology Platform, today announced that Ultragenyx Pharmaceutical Inc. has exercised an option for an exclusive worldwide license to REGENXBIO's NAV Vectors, including NAV AAV9, for the treatment of CDKL5 Deficiency Disorder (CDD).