X0306 4 2017-10-10 0 0001649904 RHYTHM PHARMACEUTICALS, INC. RYTM 0001482716 MPM BIOVENTURES V, L.P. C/O MPM ASSET MANAGEMENT 450 KENDALL STREET CAMBRIDGE MA 02142 0 0 1 0 0001134657 EVNIN LUKE C/O MPM ASSET MANAGEMENT 450 KENDALL STREET CAMBRIDGE MA 02142 0 0 1 0 0001134655 GADICKE ANSBERT C/O MPM ASSET MANAGEMENT 450 KENDALL STREET CAMBRIDGE MA 02142 0 0 1 0 0001541412 MPM ASSET MANAGEMENT INVESTORS BV5 LLC C/O MPM ASSET MANAGMENT 450 KENDALL STREET CAMBRIDGE MA 02142 0 0 1 0 0001482714 MPM BIOVENTURES V GP LLC C/O MPM ASSET MANAGEMENT 450 KENDALL STREET CAMBRIDGE MA 02142 0 0 1 0 0001482715 MPM BIOVENTURES V LLC C/O MPM ASSET MANAGEMENT 450 KENDALL STREET CAMBRIDGE MA 02142 0 0 1 0 Common Stock 2017-10-10 4 C 0 2567014 A 2596392 I See Footnote Common Stock 2017-10-10 4 P 0 100000 17.00 A 2696392 I See Footnote Series A Preferred Stock 2017-10-10 4 C 0 7651831 0.00 D Common Stock 834441 0 I See Footnote Series A-1 Junior Preferred Stock 2017-10-10 4 C 0 15887703 0.00 D Common Stock 1732573 0 I See Footnote Each share of preferred stock converted into approximately 0.10905125 shares of common stock upon the closing of the issuer's initial public offering. The shares had no expiration date. The shares are held as follows: 2,499,299 by MPM BioVentures V, L.P. ("BV V") and 97,093 by MPM Asset Management Investors BV5 LLC ("AM BV5"). MPM BioVentures V GP LLC and MPM BioVentures V LLC ("BV LLC") are the direct and indirect general partners of BV V and BV LLC is the manager of AM BV5. Ansbert Gadicke, Luke Evnin and Todd Foley are the members of BV LLC. Mr. Foley is a director of the Issuer and has separately filed a Form 4. Each Reporting Person disclaims beneficial ownership of the securities except to the extent of his or its respective pecuniary interest therein. Shares were purchased as follows: 96,260 by BV V and 3,740 by AM BV5. Shares are held as follows: 2,595,559 by BV V and 100,833 by AM BV5. Each Reporting Person disclaims beneficial ownership of the securities except to the extent of his or its respective pecuniary interest therein. The shares of Series A Preferred Stock were held as follows: 7,365,688 by BV V and 286,143 by AM BV5. The shares of Series A-1 Junior Preferred Stock were held as follows: 15,293,569 by BV V and 594,134 by AM BV5. By Luke Evnin, member of MPM BioVentures V LLC, the managing member of MPM BioVentures V GP LLC, the general partner of MPM BioVentures V, L.P. /s/ Luke Evnin 2017-10-11 /s/ Luke Evnin 2017-10-11 /s/ Ansbert Gadicke 2017-10-11 By Luke Evnin, member of MPM BioVentures V LLC, the manager of MPM Asset Management Investors BV5 LLC /s/ Luke Evnin 2017-10-11 By Luke Evnin, member of MPM BioVentures V LLC, the managing member of MPM BioVentures V GP LLC /s/ Luke Evnin 2017-10-11 By Luke Evnin, member of MPM BioVentures V LLC /s/ Luke Evnin 2017-10-11