REGENXBIO (RGNX) Form 3 REGENXBIO / James E Flynn ownership change

Joint Filer Information

Names:	Deerfield Mgmt III, L.P., Deerfield Management Company, L.P., Deerfield Private Design Fund III, L.P.
Address:	780 Third Avenue, 37th Floor New York, NY  10017
Designated Filer:	James E. Flynn
Issuer and Ticker Symbol:	REGENXBIO Inc. [RGNX]
Date of Event Requiring Statement:	September 16, 2015

The undersigned, Deerfield Mgmt III, L.P.,  Deerfield Management Company, L.P. and Deerfield Private Design Fund III, L.P. are jointly filing the attached Initial Statement of Beneficial Ownership on Form 3 with James E. Flynn with respect to the beneficial ownership of securities of REGENXBIO Inc.

Signatures:

DEERFIELD MGMT III, L.P. By:  J.E. Flynn Capital III, LLC, General Partner By: /s/ Jonathan Isler        Jonathan Isler, Attorney-In-Fact	DEERFIELD PRIVATE DESIGN FUND III, L.P. By:  Deerfield Mgmt III, L.P., General Partner By:  J.E. Flynn Capital III, LLC, General Partner By: /s/ Jonathan Isler        Jonathan Isler, Attorney-In-Fact
DEERFIELD MANAGEMENT COMPANY, L.P. By:  Flynn Management LLC, General Partner By: /s/ Jonathan Isler        Jonathan Isler, Attorney-In-Fact