Dimension Therapeutics, Inc. Watch

from S-3 37 pages Dimension Therapeutics, Inc. Issuer and [Trustee], Trustee Indenture Dated as of [•], 201[•] Subordinated Debt Securities

from S-3 37 pages Dimension Therapeutics, Inc. Issuer and [Trustee], Trustee Indenture Dated as of [•], 201[•] Senior Debt Securities

from S-1/A 2 pages Proof Proof Dimension Therapeutics, Inc. Incorporated Under the Laws of the State of Delaware Common Stock See Reverse for Certain Definitions This Certifies That: Proof Is the Owner of Fully Paid and Non-Assessable Shares of Common Stock of $0.0001 Par Value Each of Dimension Therapeutics, Inc. Transferable on the Books of the Corporation in Person or by Attorney Upon Surrender of This Certificate Duly Endorsed or Assigned. This Certificate and the Shares Represented Hereby Are Subject to the Laws of the State of Delaware, and to the Certificate of Incorporation and Bylaws of the Corporation, as Now or Hereafter Amended. This Certificate Is Not Valid Until Countersigned by the Transfer Agent. Witness the Facsimile Seal of the Corporation and the Facsimile Signatures of Its Duly Authorized Officers. Dated: Secretary President Countersigned and Registered: American Stock Transfer & Trust Company, LLC Brooklyn, Ny Transfer Agent and Registrar By: Authorized Signature Cusip25433v 10 5 Shares Number

from S-1 10 pages Warrant to Purchase Stock

from S-1 35 pages Dimension Therapeutics, Inc. Amended and Restated Investors’ Rights Agreement April 20, 2015

from DRS 10 pages Warrant to Purchase Stock

from DRS 35 pages Dimension Therapeutics, Inc. Amended and Restated Investors’ Rights Agreement April 20, 2015