Sec Form 4 Filing - Jenkins Annalisa @ Dimension Therapeutics, Inc. - 2017-11-07

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Jenkins Annalisa 2. Issuer Name and Ticker or Trading Symbol Dimension Therapeutics, Inc. [ DMTX] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) President and CEO (Last) (First) (Middle) C/O DIMENSION THERAPEUTICS, INC., 840 MEMORIAL DRIVE, 4TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 11/07/2017 (Street) CAMBRIDGE, MA02139 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Stock Option (Right to Buy) $ 0.56 11/07/2017 D 481,696 ( 1 ) 09/24/2024 Common Stock 481,696 ( 1 ) 0 D Stock Option (Right to Buy) $ 3.57 11/07/2017 D 74,375 ( 2 ) 04/28/2025 Common Stock 74,375 ( 2 ) 0 D Stock Option (Right to Buy) $ 4.09 11/07/2017 D 342,113 ( 3 ) 06/02/2025 Common Stock 342,113 ( 3 ) 0 D Stock Option (Right to Buy) $ 7.14 11/07/2017 D 160,000 ( 4 ) 01/31/2026 Common Stock 160,000 ( 4 ) 0 D Stock Option (Right to Buy) $ 1.9 11/07/2017 D 192,000 ( 5 ) 01/31/2027 Common Stock 192,000 ( 5 ) 0 D Stock Option (Right to Buy) $ 1.35 11/07/2017 D 150,000 ( 6 ) 07/02/2027 Common Stock 150,000 ( 6 ) 0 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Jenkins Annalisa C/O DIMENSION THERAPEUTICS, INC. 840 MEMORIAL DRIVE, 4TH FLOOR CAMBRIDGE, MA02139 X President and CEO Signatures /s/ Mary Thistle, as Attorney-in-Fact for Annalisa Jenkins 11/07/2017 Signature of Reporting Person Date

Explanation of Responses:

( 1 )This stock option, which vests over four years beginning September 23, 2014, at a rate of 25% after 12 months, and in 36 equal monthly installments thereafter, was assumed by Ultragenyx Pharmaceutical Inc. ("Ultragenyx"), and converted in accordance with the exchange ratio as set forth in the Agreement and Plan of Merger (the "Merger Agreement"), dated October 2, 2017, between the Issuer, Ultragenyx and Mystic River Merger Sub Inc., a direct, wholly-owned subsidiary of Ultragenyx. ( 2 )This stock option, which vests over four years beginning September 23, 2014, at a rate of 25% after 12 months, and in 36 equal monthly installments thereafter, was assumed by Ultragenyx and converted in accordance with the exchange ratio as set forth in the Merger Agreement. ( 3 )This stock option, which vests over four years beginning June 3, 2015, at a rate of 6.25% on September 23, 2015, and in 45 equal monthly installments thereafter, was assumed by Ultragenyx and converted in accordance with the exchange ratio as set forth in the Merger Agreement. ( 4 )This stock option, which vests in 48 equal monthly installments beginning January 28, 2016, was assumed by Ultragenyx and converted in accordance with the exchange ratio as set forth in the Merger Agreement. ( 5 )This stock option, which vests in 48 equal monthly installments beginning January 18, 2017, was assumed by Ultragenyx and converted in accordance with the exchange ratio as set forth in the Merger Agreement. ( 6 )This option, which vests on December 31, 2018, subject to the Reporting Person's continued service to the Issuer on such date, was assumed by Ultragenyx and converted in accordance with the exchange ratio as set forth in the Merger Agreement.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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