X0508 4 2025-05-12 false 0001590877 REGENXBIO Inc. RGNX 0001652824 Mills Kenneth T. C/O REGENXBIO INC. 9804 MEDICAL CENTER DRIVE ROCKVILLE MD 20850 true false false false true Common Stock 2025-05-12 4 M false 20602.00 3.76 A 495705.00 D Common Stock 2025-05-12 4 S false 20602.00 7.9141 D 475103.00 D Stock Options (Right to Buy) 3.76 2025-05-12 4 M false 20602.00 0.00 D 2025-05-19 Common Stock 20602.00 0.00 D This transaction was effected pursuant to a Rule 10b5-1 trading plan. This transaction was executed in multiple trades at prices ranging from $7.66 to $8.04. 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 previously granted option, representing a right to purchase a total of 275,000 shares, became exercisable as follows: 25% of the shares subject to this option vested on May 19, 2016, and the balance vested in equal monthly installments over the 36 months thereafter. /s/ Patrick J. Christmas as attorney-in-fact 2025-05-14