Sec Form 4 Filing - HURWITZ EDWARD @ Dyne Therapeutics, Inc. - 2020-07-31

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 HURWITZ EDWARD 2. Issuer Name and Ticker or Trading Symbol Dyne Therapeutics, Inc. [ DYN] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O DYNE THERAPEUTICS, INC., 830 WINTER STREET 3. Date of Earliest Transaction (MM/DD/YY) 07/31/2020 (Street) WALTHAM, MA02451 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 Common Stock 09/21/2020 C 4,614,943 A 4,614,943 I See footnote ( 3 ) Common Stock 09/21/2020 C 245,279 A 245,279 I See footnote ( 4 ) Common Stock 09/21/2020 C 91,081 A 91,081 I See footnote ( 5 )

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 Series A Preferred Stock ( 6 ) 07/31/2020 P 4,893,347 ( 6 ) ( 6 ) Common Stock 1,475,277 $ 1 13,980,992 I See footnote ( 3 ) Series A Preferred Stock ( 6 ) 07/31/2020 P 260,077 ( 6 ) ( 6 ) Common Stock 78,409 $ 1 743,076 I See footnote ( 4 ) Series A Preferred Stock ( 6 ) 07/31/2020 P 96,576 ( 6 ) ( 6 ) Common Stock 29,116 $ 1 275,932 I See footnote ( 5 ) Series B Preferred Stock ( 7 ) 08/07/2020 P 1,326,313 ( 7 ) ( 7 ) Common Stock 399,867 $ 2.811 1,326,313 I See footnote ( 3 ) Series B Preferred Stock ( 7 ) 08/07/2020 P 70,492 ( 7 ) ( 7 ) Common Stock 21,254 $ 2.811 70,492 I See footnote ( 4 ) Series B Preferred Stock ( 7 ) 08/07/2020 P 26,176 ( 7 ) ( 7 ) Common Stock 7,893 $ 2.811 26,176 I See footnote ( 5 ) Series A Preferred Stock ( 1 ) 09/21/2020 C 13,980,992 ( 1 ) ( 1 ) Common Stock 4,215,076 $ 0 0 I See footnote ( 3 ) Series A Preferred Stock ( 1 ) 09/21/2020 C 743,076 ( 1 ) ( 1 ) Common Stock 224,025 $ 0 0 I See footnote ( 4 ) Series A Preferred Stock ( 1 ) 09/21/2020 C 275,932 ( 1 ) ( 1 ) Common Stock 83,188 $ 0 0 I See footnote ( 5 ) Series B Preferred Stock ( 2 ) 09/21/2020 C 1,326,313 ( 2 ) ( 2 ) Common Stock 399,867 $ 0 0 I See footnote ( 3 ) Series B Preferred Stock ( 2 ) 09/21/2020 C 70,492 ( 2 ) ( 2 ) Common Stock 21,254 $ 0 0 I See footnote ( 4 ) Series B Preferred Stock ( 2 ) 09/21/2020 C 26,176 ( 2 ) ( 2 ) Common Stock 7,893 $ 0 0 I See footnote ( 5 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other HURWITZ EDWARD C/O DYNE THERAPEUTICS, INC. 830 WINTER STREET WALTHAM, MA02451 X X Signatures /s/ Richard Scalzo, Attorney-in-Fact 09/23/2020 Signature of Reporting Person Date

Explanation of Responses:

( 1 )On September 21, 2020, the Series A Preferred Stock automatically converted into Common Stock on a 3.3169-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date. ( 2 )On September 21, 2020, the Series B Preferred Stock automatically converted into Common Stock on a 3.3169-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date. ( 3 )The shares are held directly by MPM BioVentures 2018, L.P. ("BV 2018"). The general partner of BV 2018 is MPM BioVentures 2018 GP LLC ("BV 2018 GP"). MPM BioVentures 2018 LLC ("BV 2018 LLC") is the managing member of BV 2018 GP. The Reporting Person, Luke Evnin, Ansbert Gadicke, and Todd Foley are the Managing Directors of BV 2018 LLC. The Reporting Person disclaims Section 16 beneficial ownership of the securities held by BV 2018, except to the extent of his pecuniary interest therein, if any. ( 4 )The shares are held directly by MPM BioVentures 2018 (B), L.P. ("BV 2018(B)"). The general partner of BV 2018(B) is BV 2018 GP. BV 2018 LLC is the managing member of BV 2018 GP. The Reporting Person, Luke Evnin, Ansbert Gadicke, and Todd Foley are the Managing Directors of BV 2018 LLC. The Reporting Person disclaims Section 16 beneficial ownership of the securities held by BV 2018(B), except to the extent of his pecuniary interest therein, if any. ( 5 )The shares are held directly by MPM Asset Management Investors BV2018 LLC ("MPM Asset Management"). The manager of MPM Asset Management is BV 2018 LLC. The Reporting Person, Luke Evnin, Ansbert Gadicke, and Todd Foley are the Managing Directors of BV 2018 LLC. The Reporting Person disclaims Section 16 beneficial ownership of the securities held by MPM Asset Management, except to the extent of his pecuniary interest therein, if any. ( 6 )The Series A Preferred Stock was convertible into common stock on a 3.3169-for-one basis into the number of shares of common stock shown in Column 7 without payment of further consideration at the holder's election or upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date. ( 7 )The Series B Preferred Stock was convertible into common stock on a 3.3169-for-one basis into the number of shares of common stock shown in Column 7 without payment of further consideration at the holder's election or upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date.

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