X0306 4 2021-09-17 0 0001590877 REGENXBIO Inc. RGNX 0001652936 Fox Allan M. C/O REGENXBIO INC. 9804 MEDICAL CENTER DRIVE ROCKVILLE MD 20850 1 0 0 0 Common Stock 2021-09-17 4 S 0 48233 45.0381 D 1364309 I By DING LLC Common Stock 315000 I By HBF Gift Trust LLC Common Stock 278541 I By Fox 2020 Trust Common Stock 315000 I By AMF Gift Trust LLC Common Stock 722485 I By AMF Family Gift Trust LLC This transaction was executed in multiple trades at prices ranging from $45.00 to $45.15. The price reported above reflects the weighted average sale price. The reporting person hereby undertakes to provide upon request to the SEC staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected. The reporting person disclaims beneficial ownership of such shares except to the extent of his indirect pecuniary interest therein, and the inclusion of these shares in this report shall not be deemed an admission of beneficial ownership of all of the reported shares for purposes of Section 16 or for any other purpose. /s/ Patrick J. Christmas as attorney-in-fact 2021-09-21