Sec Form 4 Filing - Exter Neil @ RHYTHM PHARMACEUTICALS, INC. - 2017-10-10

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 Exter Neil 2. Issuer Name and Ticker or Trading Symbol RHYTHM PHARMACEUTICALS, INC. [ RYTM] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 500 BOYLSTON STREET, 11TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 10/10/2017 (Street) BOSTON, MA02116 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 10/10/2017 C 0 ( 1 ) A 0 ( 3 ) I See Footnotes ( 3 ) ( 4 )

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 Convertible Preferred Stock ( 2 ) 10/10/2017 C 0 ( 5 ) ( 2 ) ( 2 ) Common Stock 0 ( 6 ) $ 0 0 I See Footnotes ( 4 ) ( 6 ) Series A-1 Junior Preferred Stock ( 2 ) 10/10/2017 C 0 ( 5 ) ( 2 ) ( 2 ) Common Stock 0 ( 6 ) $ 0 0 I See Footnotes ( 4 ) ( 6 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Exter Neil 500 BOYLSTON STREET, 11TH FLOOR BOSTON, MA02116 X Signatures /s/ Keith Gottesdiener, as attorney-in-fact 10/12/2017 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Represents 3,963,810 shares of the Issuer's common stock held by Third Rock Ventures, L.P. (the "Fund") upon conversion of the Issuer's series A convertible preferred stock (the "Series A Preferred") and series A-1 junior preferred stock (the "Series A-1 Preferred") upon closing of the Issuer's initial public offering (the "IPO"). ( 2 )Each share of the Series A Preferred and Series A-1 Preferred converted into shares of the Issuer's common stock on a 9.17-for-one basis upon the closing of the IPO without payment or consideration. The Series A Preferred and Series A-1 Preferred were convertible at any time at the holder's election and automatically upon the closing of the IPO and had no expiration date. ( 3 )Represents (i) 3,963,810 shares of the Issuer's common stock held by the Fund upon conversion of the Series A Preferred and Series A-1 Preferred upon closing of the IPO and (ii) 17,627 shares of the Issuer's common stock held by the Fund prior to the closing of the IPO. ( 4 )The Reporting Person is a partner of Third Rock Ventures GP, L.P., which is the general partner of the Fund. The Reporting Person disclaims beneficial ownership over the shares held by the Fund, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares. ( 5 )Prior to the conversion, the Fund held 9,479,502 and 26,868,642 shares of the Series A Preferred and Series A-1 Preferred, respectively. ( 6 )Prior to the conversion, the Fund held 1,033,751 and 2,930,059 shares of the Series A Preferred and Series A-1 Preferred, respectively, on an as converted to common stock basis.

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