Exhibit B

Joint Filing Statement

I, the undersigned, hereby express my agreement that the attached Schedule 13D (and any amendments thereto) relating to the beneficial ownership by the undersigned of the equity securities of Rhythm Pharmaceuticals, Inc. is filed on behalf of each of the undersigned.

Date: February 11, 2019
MPM BIOVENTURES V GP LLC
By: MPM BioVentures V LLC,
its Managing Member
By:	/s/ Todd Foley
Name:	Todd Foley
Title:	Member
MPM BIOVENTURES V LLC
By:	/s/ Todd Foley
Name:	Todd Foley
Title:	Member
MPM BIOVENTURES V, L.P.
By: MPM BioVentures V GP LLC, its General Partner
By: MPM BioVentures V LLC, its Managing Member
By:	/s/ Todd Foley
Name:	Todd Foley
Title:	Member
MPM ASSET MANAGEMENT INVESTORS BV5 LLC
By:	/s/ Howard Rubin
Name:	Howard Rubin
Title:	Director
By:	/s/ Todd Foley
Name:	Todd Foley
By:	/s/ Luke Evnin
Name:	Luke Evnin
By:	/s/ Ansbert Gadicke
Name:	Ansbert Gadicke