RYTM

SEC source: 0001104659-17-061574 · a4.xml · derivative · entry 5

Ipsen, S.A. · CIK 0001370483 · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · The owner of record of the securities is Sutrepa SAS.Sutrepa SAS is controlled by Ipsen SA

Disclosed balance after: 0

Underlying: Common Stock · 167,938 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: In connection with the closing of the Issuer's initial public offering, each share 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") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred and the Series A-1 Preferred had no expiration date.

F2 · shares: Reflects the number of shares of Series A Preferred and Series A-1 Preferred, as applicable, held by the Reporting Person on an as-converted to common stock basis.

F1 · derivative.exercise_date: In connection with the closing of the Issuer's initial public offering, each share 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") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred and the Series A-1 Preferred had no expiration date.

F1 · derivative.expiration_date: In connection with the closing of the Issuer's initial public offering, each share 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") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred and the Series A-1 Preferred had no expiration date.

F2 · derivative.underlying_shares: Reflects the number of shares of Series A Preferred and Series A-1 Preferred, as applicable, held by the Reporting Person on an as-converted to common stock basis.

SEC source: 0001104659-17-061574 · a4.xml · derivative · entry 4

Ipsen, S.A. · CIK 0001370483 · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · The owner of record of the securities is Sutrepa SAS.Sutrepa SAS is controlled by Ipsen SA

Disclosed balance after: 0

Underlying: Common Stock · 45,831 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: In connection with the closing of the Issuer's initial public offering, each share 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") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred and the Series A-1 Preferred had no expiration date.

F2 · shares: Reflects the number of shares of Series A Preferred and Series A-1 Preferred, as applicable, held by the Reporting Person on an as-converted to common stock basis.

F1 · derivative.exercise_date: In connection with the closing of the Issuer's initial public offering, each share 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") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred and the Series A-1 Preferred had no expiration date.

F1 · derivative.expiration_date: In connection with the closing of the Issuer's initial public offering, each share 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") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred and the Series A-1 Preferred had no expiration date.

F2 · derivative.underlying_shares: Reflects the number of shares of Series A Preferred and Series A-1 Preferred, as applicable, held by the Reporting Person on an as-converted to common stock basis.

SEC source: 0001104659-17-061574 · a4.xml · nonDerivative · entry 3

Ipsen, S.A. · CIK 0001370483 · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · The owner of record of the securities is Ipsen Pharma, S.A.S., which is controlled by Ipsen SA

Disclosed balance after: 833,099

SEC source: 0001104659-17-061574 · a4.xml · nonDerivative · entry 2

Ipsen, S.A. · CIK 0001370483 · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · The owner of record of the securities is Sutrepa SAS. Sutrepa SAS is controlled by Ipsen SA

Disclosed balance after: 813,099

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: In connection with the closing of the Issuer's initial public offering, each share 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") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred and the Series A-1 Preferred had no expiration date.

SEC source: 0001104659-17-061574 · a4.xml · nonDerivative · entry 1

Ipsen, S.A. · CIK 0001370483 · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · The owner of record of the securities is Sutrepa SAS. Sutrepa SAS is controlled by Ipsen SA

Disclosed balance after: 645,161

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: In connection with the closing of the Issuer's initial public offering, each share 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") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred and the Series A-1 Preferred had no expiration date.

SEC source: 0001104659-17-061577 · a4.xml · derivative · entry 3

Meeker David P · CIK 0001385155 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 54,525 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: In connection with the closing of the Issuer's initial public offering, each share of the Issuer's series A convertible preferred stock (the "Series A Preferred") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred had no expiration date.

F2 · shares: Reflects the number of shares of Series A Preferred held by the Reporting Person on an as-converted to common stock basis.

F1 · derivative.exercise_date: In connection with the closing of the Issuer's initial public offering, each share of the Issuer's series A convertible preferred stock (the "Series A Preferred") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred had no expiration date.

F1 · derivative.expiration_date: In connection with the closing of the Issuer's initial public offering, each share of the Issuer's series A convertible preferred stock (the "Series A Preferred") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred had no expiration date.

F2 · derivative.underlying_shares: Reflects the number of shares of Series A Preferred held by the Reporting Person on an as-converted to common stock basis.

SEC source: 0001104659-17-061577 · a4.xml · nonDerivative · entry 2

Meeker David P · CIK 0001385155 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 101,335

SEC source: 0001104659-17-061577 · a4.xml · nonDerivative · entry 1

Meeker David P · CIK 0001385155 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 76,335

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: In connection with the closing of the Issuer's initial public offering, each share of the Issuer's series A convertible preferred stock (the "Series A Preferred") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred had no expiration date.

SEC source: 0001104659-17-061576 · a4.xml · derivative · entry 2

Gottesdiener Keith Michael · CIK 0001615856 · Director · CEO and President

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 27,262 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: In connection with the closing of the Issuer's initial public offering, each share of the Issuer's series A convertible preferred stock (the "Series A Preferred") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred had no expiration date.

F2 · shares: Reflects the number of shares of Series A Preferred held by the Reporting Person on an as-converted to common stock basis.

F1 · derivative.exercise_date: In connection with the closing of the Issuer's initial public offering, each share of the Issuer's series A convertible preferred stock (the "Series A Preferred") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred had no expiration date.

F1 · derivative.expiration_date: In connection with the closing of the Issuer's initial public offering, each share of the Issuer's series A convertible preferred stock (the "Series A Preferred") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred had no expiration date.

F2 · derivative.underlying_shares: Reflects the number of shares of Series A Preferred held by the Reporting Person on an as-converted to common stock basis.

SEC source: 0001104659-17-061576 · a4.xml · nonDerivative · entry 1

Gottesdiener Keith Michael · CIK 0001615856 · Director · CEO and President

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 585,539

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: In connection with the closing of the Issuer's initial public offering, each share of the Issuer's series A convertible preferred stock (the "Series A Preferred") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred had no expiration date.

SEC source: 0001104659-17-061562 · a4.xml · derivative · entry 2

Hadley Harbor Master Investors (Cayman) L.P. · CIK 0001641080 · 10% owner

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 545,256 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: The Series A Convertible Preferred Stock converted into Common Stock on a 9.17-for-one basis upon the closing of the Issuer's initial public offering. The shares had no expiration date.

F1 · derivative.exercise_date: The Series A Convertible Preferred Stock converted into Common Stock on a 9.17-for-one basis upon the closing of the Issuer's initial public offering. The shares had no expiration date.

F1 · derivative.expiration_date: The Series A Convertible Preferred Stock converted into Common Stock on a 9.17-for-one basis upon the closing of the Issuer's initial public offering. The shares had no expiration date.

SEC source: 0001104659-17-061562 · a4.xml · nonDerivative · entry 1

Hadley Harbor Master Investors (Cayman) L.P. · CIK 0001641080 · 10% owner

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 545,256

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: The Series A Convertible Preferred Stock converted into Common Stock on a 9.17-for-one basis upon the closing of the Issuer's initial public offering. The shares had no expiration date.

SEC source: 0001209191-17-056612 · doc4.xml · derivative · entry 4

MPM BIOVENTURES V, L.P. · CIK 0001482716 · 10% owner

EVNIN LUKE · CIK 0001134657 · 10% owner

GADICKE ANSBERT · CIK 0001134655 · 10% owner

MPM ASSET MANAGEMENT INVESTORS BV5 LLC · CIK 0001541412 · 10% owner

MPM BIOVENTURES V GP LLC · CIK 0001482714 · 10% owner

MPM BIOVENTURES V LLC · CIK 0001482715 · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 0

Underlying: Common Stock · 1,732,573 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: 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.

F1 · derivative.exercise_date: 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.

F1 · derivative.expiration_date: 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.

F6 · ownership.nature: 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.

SEC source: 0001209191-17-056612 · doc4.xml · derivative · entry 3

MPM BIOVENTURES V, L.P. · CIK 0001482716 · 10% owner

EVNIN LUKE · CIK 0001134657 · 10% owner

GADICKE ANSBERT · CIK 0001134655 · 10% owner

MPM ASSET MANAGEMENT INVESTORS BV5 LLC · CIK 0001541412 · 10% owner

MPM BIOVENTURES V GP LLC · CIK 0001482714 · 10% owner

MPM BIOVENTURES V LLC · CIK 0001482715 · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 0

Underlying: Common Stock · 834,441 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: 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.

F1 · derivative.exercise_date: 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.

F1 · derivative.expiration_date: 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.

F5 · ownership.nature: The shares of Series A Preferred Stock were held as follows: 7,365,688 by BV V and 286,143 by AM BV5.

SEC source: 0001209191-17-056612 · doc4.xml · nonDerivative · entry 2

MPM BIOVENTURES V, L.P. · CIK 0001482716 · 10% owner

EVNIN LUKE · CIK 0001134657 · 10% owner

GADICKE ANSBERT · CIK 0001134655 · 10% owner

MPM ASSET MANAGEMENT INVESTORS BV5 LLC · CIK 0001541412 · 10% owner

MPM BIOVENTURES V GP LLC · CIK 0001482714 · 10% owner

MPM BIOVENTURES V LLC · CIK 0001482715 · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 2,696,392

F3 · shares: Shares were purchased as follows: 96,260 by BV V and 3,740 by AM BV5.

F4 · ownership.nature: 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.

SEC source: 0001209191-17-056612 · doc4.xml · nonDerivative · entry 1

MPM BIOVENTURES V, L.P. · CIK 0001482716 · 10% owner

EVNIN LUKE · CIK 0001134657 · 10% owner

GADICKE ANSBERT · CIK 0001134655 · 10% owner

MPM ASSET MANAGEMENT INVESTORS BV5 LLC · CIK 0001541412 · 10% owner

MPM BIOVENTURES V GP LLC · CIK 0001482714 · 10% owner

MPM BIOVENTURES V LLC · CIK 0001482715 · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 2,596,392

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: 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.

F2 · ownership.nature: 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.

SEC source: 0000899243-17-024006 · doc4.xml · derivative · entry 3

THIRD ROCK VENTURES LP · CIK 0001408591 · 10% owner

Third Rock Ventures GP, L.P. · CIK 0001578976 · 10% owner

TRV GP, LLC · CIK 0001578973 · 10% owner

LEVIN MARK J · CIK 0001180428 · 10% owner

STARR KEVIN P · CIK 0001192603 · 10% owner

TEPPER ROBERT I · CIK 0001192595 · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 2,930,059 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: The Series A Convertible Preferred Stock and Series A-1 Junior Preferred Stock converted into Common Stock on a 9.17-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series A Convertible Preferred Stock and Series A-1 Junior Preferred Stock were convertible at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The Preferred Stock had no expiration date.

F2 · derivative.exercise_date: The Series A Convertible Preferred Stock and Series A-1 Junior Preferred Stock converted into Common Stock on a 9.17-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series A Convertible Preferred Stock and Series A-1 Junior Preferred Stock were convertible at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The Preferred Stock had no expiration date.

F2 · derivative.expiration_date: The Series A Convertible Preferred Stock and Series A-1 Junior Preferred Stock converted into Common Stock on a 9.17-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series A Convertible Preferred Stock and Series A-1 Junior Preferred Stock were convertible at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The Preferred Stock had no expiration date.

F3 · ownership.direct: These shares are directly held by TRV. The general partner of TRV is Third Rock Ventures GP, L.P. ("TRV GP"). The general partner of TRV GP is TRV GP, LLC ("TRV GP LLC"). The individual managers of TRV GP LLC are Mark Levin ("Levin"), Kevin Starr ("Starr") and Dr. Robert Tepper ("Tepper"). Each of TRV GP, TRV GP LLC, Levin, Starr and Tepper disclaims beneficial ownership of these shares except to the extent of its or his pecuniary interest therein, if any, and this report shall not be deemed an admission that it or he is the beneficial owner of such shares.

SEC source: 0000899243-17-024006 · doc4.xml · derivative · entry 2

THIRD ROCK VENTURES LP · CIK 0001408591 · 10% owner

Third Rock Ventures GP, L.P. · CIK 0001578976 · 10% owner

TRV GP, LLC · CIK 0001578973 · 10% owner

LEVIN MARK J · CIK 0001180428 · 10% owner

STARR KEVIN P · CIK 0001192603 · 10% owner

TEPPER ROBERT I · CIK 0001192595 · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 1,033,751 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: The Series A Convertible Preferred Stock and Series A-1 Junior Preferred Stock converted into Common Stock on a 9.17-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series A Convertible Preferred Stock and Series A-1 Junior Preferred Stock were convertible at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The Preferred Stock had no expiration date.

F2 · derivative.exercise_date: The Series A Convertible Preferred Stock and Series A-1 Junior Preferred Stock converted into Common Stock on a 9.17-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series A Convertible Preferred Stock and Series A-1 Junior Preferred Stock were convertible at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The Preferred Stock had no expiration date.

F2 · derivative.expiration_date: The Series A Convertible Preferred Stock and Series A-1 Junior Preferred Stock converted into Common Stock on a 9.17-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series A Convertible Preferred Stock and Series A-1 Junior Preferred Stock were convertible at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The Preferred Stock had no expiration date.

F3 · ownership.direct: These shares are directly held by TRV. The general partner of TRV is Third Rock Ventures GP, L.P. ("TRV GP"). The general partner of TRV GP is TRV GP, LLC ("TRV GP LLC"). The individual managers of TRV GP LLC are Mark Levin ("Levin"), Kevin Starr ("Starr") and Dr. Robert Tepper ("Tepper"). Each of TRV GP, TRV GP LLC, Levin, Starr and Tepper disclaims beneficial ownership of these shares except to the extent of its or his pecuniary interest therein, if any, and this report shall not be deemed an admission that it or he is the beneficial owner of such shares.

SEC source: 0000899243-17-024006 · doc4.xml · nonDerivative · entry 1

THIRD ROCK VENTURES LP · CIK 0001408591 · 10% owner

Third Rock Ventures GP, L.P. · CIK 0001578976 · 10% owner

TRV GP, LLC · CIK 0001578973 · 10% owner

LEVIN MARK J · CIK 0001180428 · 10% owner

STARR KEVIN P · CIK 0001192603 · 10% owner

TEPPER ROBERT I · CIK 0001192595 · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 3,981,437

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · shares: Represents the total number of shares of Common Stock received by Third Rock Ventures, L.P. ("TRV") upon conversion of the Series A Convertible Preferred Stock and Series A-1 Junior Preferred Stock of the Issuer in connection with the closing of the Issuer's initial public offering.

F2 · price: The Series A Convertible Preferred Stock and Series A-1 Junior Preferred Stock converted into Common Stock on a 9.17-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series A Convertible Preferred Stock and Series A-1 Junior Preferred Stock were convertible at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The Preferred Stock had no expiration date.

F3 · ownership.direct: These shares are directly held by TRV. The general partner of TRV is Third Rock Ventures GP, L.P. ("TRV GP"). The general partner of TRV GP is TRV GP, LLC ("TRV GP LLC"). The individual managers of TRV GP LLC are Mark Levin ("Levin"), Kevin Starr ("Starr") and Dr. Robert Tepper ("Tepper"). Each of TRV GP, TRV GP LLC, Levin, Starr and Tepper disclaims beneficial ownership of these shares except to the extent of its or his pecuniary interest therein, if any, and this report shall not be deemed an admission that it or he is the beneficial owner of such shares.

SEC source: 0001209191-17-056611 · doc4.xml · derivative · entry 5

Foley Todd · CIK 0001473930 · Director · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 0

Underlying: Common Stock · 1,732,573 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: 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.

F1 · derivative.exercise_date: 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.

F1 · derivative.expiration_date: 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.

F8 · ownership.nature: 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.

SEC source: 0001209191-17-056611 · doc4.xml · derivative · entry 4

Foley Todd · CIK 0001473930 · Director · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 0

Underlying: Common Stock · 834,441 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: 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.

F1 · derivative.exercise_date: 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.

F1 · derivative.expiration_date: 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.

F7 · ownership.nature: The shares of Series A Preferred Stock were held as follows: 7,365,688 by BV V and 286,143 by AM BV5.

SEC source: 0001209191-17-056611 · doc4.xml · nonDerivative · entry 2

Foley Todd · CIK 0001473930 · Director · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 2,696,392

F3 · shares: Shares were purchased as follows: 96,260 by BV V and 3,740 by AM BV5.

F4 · ownership.nature: Shares are held as follows: 2,595,559 by BV V and 100,833 by AM BV5. The Reporting Person disclaims beneficial ownership of the securities except to the extent of his pecuniary interest therein.

SEC source: 0001209191-17-056611 · doc4.xml · nonDerivative · entry 1

Foley Todd · CIK 0001473930 · Director · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 2,596,392

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: 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.

F2 · ownership.nature: 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. The Reporting Person disclaims beneficial ownership of the securities except to the extent of his pecuniary interest therein.

SEC source: 0001104659-17-061969 · a4.xml · derivative · entry 3

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

Underlying: Common Stock · 0 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: 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.

F5 · shares: 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.

F2 · derivative.exercise_date: 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.

F2 · derivative.expiration_date: 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.

F6 · derivative.underlying_shares: 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.

F4 · ownership.nature: 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.

F6 · ownership.nature: 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.

SEC source: 0001104659-17-061969 · a4.xml · derivative · entry 2

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

Underlying: Common Stock · 0 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: 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.

F5 · shares: 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.

F2 · derivative.exercise_date: 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.

F2 · derivative.expiration_date: 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.

F6 · derivative.underlying_shares: 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.

F4 · ownership.nature: 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.

F6 · ownership.nature: 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.

SEC source: 0001104659-17-061969 · a4.xml · nonDerivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · shares: 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").

F2 · price: 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.

F3 · balance_after: 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.

F3 · ownership.nature: 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.

F4 · ownership.nature: 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.

SEC source: 0001104659-17-061575 · a4.xml · derivative · entry 5

PFIZER INC · CIK 0000078003 · 10% owner

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 940,125 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: In connection with the closing of the Issuer's initial public offering, each share 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") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred and the Series A-1 Preferred had no expiration date.

F2 · shares: Reflects the number of shares of Series A Preferred and Series A-1 Preferred, as applicable, held by the Reporting Person on an as-converted to common stock basis.

F1 · derivative.exercise_date: In connection with the closing of the Issuer's initial public offering, each share 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") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred and the Series A-1 Preferred had no expiration date.

F1 · derivative.expiration_date: In connection with the closing of the Issuer's initial public offering, each share 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") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred and the Series A-1 Preferred had no expiration date.

F2 · derivative.underlying_shares: Reflects the number of shares of Series A Preferred and Series A-1 Preferred, as applicable, held by the Reporting Person on an as-converted to common stock basis.

SEC source: 0001104659-17-061575 · a4.xml · derivative · entry 4

PFIZER INC · CIK 0000078003 · 10% owner

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 447,514 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: In connection with the closing of the Issuer's initial public offering, each share 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") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred and the Series A-1 Preferred had no expiration date.

F2 · shares: Reflects the number of shares of Series A Preferred and Series A-1 Preferred, as applicable, held by the Reporting Person on an as-converted to common stock basis.

F1 · derivative.exercise_date: In connection with the closing of the Issuer's initial public offering, each share 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") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred and the Series A-1 Preferred had no expiration date.

F1 · derivative.expiration_date: In connection with the closing of the Issuer's initial public offering, each share 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") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred and the Series A-1 Preferred had no expiration date.

F2 · derivative.underlying_shares: Reflects the number of shares of Series A Preferred and Series A-1 Preferred, as applicable, held by the Reporting Person on an as-converted to common stock basis.

SEC source: 0001104659-17-061575 · a4.xml · nonDerivative · entry 3

PFIZER INC · CIK 0000078003 · 10% owner

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 1,427,639

SEC source: 0001104659-17-061575 · a4.xml · nonDerivative · entry 2

PFIZER INC · CIK 0000078003 · 10% owner

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 1,387,639

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: In connection with the closing of the Issuer's initial public offering, each share 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") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred and the Series A-1 Preferred had no expiration date.

SEC source: 0001104659-17-061575 · a4.xml · nonDerivative · entry 1

PFIZER INC · CIK 0000078003 · 10% owner

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 447,514

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: In connection with the closing of the Issuer's initial public offering, each share 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") converted into the Issuer's common stock on a 9.17-for-one basis without payment or consideration. The Series A Preferred and the Series A-1 Preferred had no expiration date.

SEC source: 0001638599-17-001008 · doc4_5014.xml · derivative · entry 6

BAKER BROS. ADVISORS LP · CIK 0001263508 · Former 10% owner

Baker Bros. Advisors (GP) LLC · CIK 0001580575 · Former 10% owner

BAKER FELIX · CIK 0001087940 · Former 10% owner

BAKER JULIAN · CIK 0001087939 · Former 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 1,081,051 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F5 · derivative.exercise_price: Effective upon the closing of the Issuer's IPO, the Series A Preferred shares of the Issuer were converted at the Conversion Ratio without consideration into the number of common shares of the Issuer shown in Column 7. The Series A Preferred shares did not have an expiration date and were convertible at any time, at the holder's election, into common shares of the Issuer.

F6 · price: Pursuant to Instruction 4(c)(iii), this response has been left blank.

F5 · derivative.exercise_date: Effective upon the closing of the Issuer's IPO, the Series A Preferred shares of the Issuer were converted at the Conversion Ratio without consideration into the number of common shares of the Issuer shown in Column 7. The Series A Preferred shares did not have an expiration date and were convertible at any time, at the holder's election, into common shares of the Issuer.

F5 · derivative.expiration_date: Effective upon the closing of the Issuer's IPO, the Series A Preferred shares of the Issuer were converted at the Conversion Ratio without consideration into the number of common shares of the Issuer shown in Column 7. The Series A Preferred shares did not have an expiration date and were convertible at any time, at the holder's election, into common shares of the Issuer.

F3 · ownership.nature: After giving effect to the transactions reported herein, and as a result of their ownership interest in Baker Brothers Life Sciences Capital (GP), LLC, Julian C. Baker and Felix J. Baker may be deemed to have an indirect pecuniary interest in shares of the Issuer's common stock reported in column 5 of Table I directly held by Baker Brothers Life Sciences, L.P. ("Life Sciences" and together with 667, the "Funds"), a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital, L.P., a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital (GP), LLC, due to Baker Brothers Life Sciences Capital, L.P.'s right to receive an allocation of a portion of the profits from Life Sciences.

F7 · ownership.nature: Baker Bros. Advisors LP (the "Adviser") serves as the Investment Adviser to the Funds. In connection with the services provided by the Adviser, the Adviser receives an asset-based management fee that does not confer any pecuniary interest in the securities held by the Funds. Baker Bros. Advisors (GP) LLC (the "Adviser GP") is the Adviser's sole general partner. Julian C. Baker and Felix J. Baker are principals of the Adviser GP. The Adviser has complete and unlimited discretion and authority with respect to the investment and voting power of the securities held by the Funds.

F8 · ownership.nature: The general partners of the Funds relinquished to the Adviser all discretion and authority with respect to the investment and voting power of the securities held by the Funds. Julian C. Baker, Felix J. Baker, the Adviser GP and the Adviser disclaim beneficial ownership of the securities held directly by the Funds except to the extent of their pecuniary interest therein, and this report shall not be deemed an admission that any of Julian C. Baker, Felix J. Baker, the Adviser GP or the Adviser is a beneficial owner of such securities for purposes of Section 16 or any other purpose.

SEC source: 0001638599-17-001008 · doc4_5014.xml · derivative · entry 5

BAKER BROS. ADVISORS LP · CIK 0001263508 · Former 10% owner

Baker Bros. Advisors (GP) LLC · CIK 0001580575 · Former 10% owner

BAKER FELIX · CIK 0001087940 · Former 10% owner

BAKER JULIAN · CIK 0001087939 · Former 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 82,969 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F5 · derivative.exercise_price: Effective upon the closing of the Issuer's IPO, the Series A Preferred shares of the Issuer were converted at the Conversion Ratio without consideration into the number of common shares of the Issuer shown in Column 7. The Series A Preferred shares did not have an expiration date and were convertible at any time, at the holder's election, into common shares of the Issuer.

F6 · price: Pursuant to Instruction 4(c)(iii), this response has been left blank.

F5 · derivative.exercise_date: Effective upon the closing of the Issuer's IPO, the Series A Preferred shares of the Issuer were converted at the Conversion Ratio without consideration into the number of common shares of the Issuer shown in Column 7. The Series A Preferred shares did not have an expiration date and were convertible at any time, at the holder's election, into common shares of the Issuer.

F5 · derivative.expiration_date: Effective upon the closing of the Issuer's IPO, the Series A Preferred shares of the Issuer were converted at the Conversion Ratio without consideration into the number of common shares of the Issuer shown in Column 7. The Series A Preferred shares did not have an expiration date and were convertible at any time, at the holder's election, into common shares of the Issuer.

F2 · ownership.nature: After giving effect to the transactions reported herein, and as a result of their ownership interest in Baker Biotech Capital (GP), LLC, Julian C. Baker and Felix J. Baker may be deemed to have an indirect pecuniary interest in shares of the Issuer's common stock reported in column 5 of Table I directly held by 667, L.P. ("667"), a limited partnership of which the sole general partner is Baker Biotech Capital, L.P., a limited partnership of which the sole general partner is Baker Biotech Capital (GP), LLC, due to Baker Biotech Capital, L.P.'s right to receive an allocation of a portion of the profits from 667.

F7 · ownership.nature: Baker Bros. Advisors LP (the "Adviser") serves as the Investment Adviser to the Funds. In connection with the services provided by the Adviser, the Adviser receives an asset-based management fee that does not confer any pecuniary interest in the securities held by the Funds. Baker Bros. Advisors (GP) LLC (the "Adviser GP") is the Adviser's sole general partner. Julian C. Baker and Felix J. Baker are principals of the Adviser GP. The Adviser has complete and unlimited discretion and authority with respect to the investment and voting power of the securities held by the Funds.

F8 · ownership.nature: The general partners of the Funds relinquished to the Adviser all discretion and authority with respect to the investment and voting power of the securities held by the Funds. Julian C. Baker, Felix J. Baker, the Adviser GP and the Adviser disclaim beneficial ownership of the securities held directly by the Funds except to the extent of their pecuniary interest therein, and this report shall not be deemed an admission that any of Julian C. Baker, Felix J. Baker, the Adviser GP or the Adviser is a beneficial owner of such securities for purposes of Section 16 or any other purpose.

SEC source: 0001638599-17-001008 · doc4_5014.xml · nonDerivative · entry 4

BAKER BROS. ADVISORS LP · CIK 0001263508 · Former 10% owner

Baker Bros. Advisors (GP) LLC · CIK 0001580575 · Former 10% owner

BAKER FELIX · CIK 0001087940 · Former 10% owner

BAKER JULIAN · CIK 0001087939 · Former 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 1,878,242

F4 · shares: On October 5, 2017, 667 and Life Sciences purchased 87,809 and 797,191 shares of common stock of the Issuer at a price of $17.00 per share, respectively, pursuant to an IPO.

F3 · ownership.nature: After giving effect to the transactions reported herein, and as a result of their ownership interest in Baker Brothers Life Sciences Capital (GP), LLC, Julian C. Baker and Felix J. Baker may be deemed to have an indirect pecuniary interest in shares of the Issuer's common stock reported in column 5 of Table I directly held by Baker Brothers Life Sciences, L.P. ("Life Sciences" and together with 667, the "Funds"), a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital, L.P., a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital (GP), LLC, due to Baker Brothers Life Sciences Capital, L.P.'s right to receive an allocation of a portion of the profits from Life Sciences.

F7 · ownership.nature: Baker Bros. Advisors LP (the "Adviser") serves as the Investment Adviser to the Funds. In connection with the services provided by the Adviser, the Adviser receives an asset-based management fee that does not confer any pecuniary interest in the securities held by the Funds. Baker Bros. Advisors (GP) LLC (the "Adviser GP") is the Adviser's sole general partner. Julian C. Baker and Felix J. Baker are principals of the Adviser GP. The Adviser has complete and unlimited discretion and authority with respect to the investment and voting power of the securities held by the Funds.

F8 · ownership.nature: The general partners of the Funds relinquished to the Adviser all discretion and authority with respect to the investment and voting power of the securities held by the Funds. Julian C. Baker, Felix J. Baker, the Adviser GP and the Adviser disclaim beneficial ownership of the securities held directly by the Funds except to the extent of their pecuniary interest therein, and this report shall not be deemed an admission that any of Julian C. Baker, Felix J. Baker, the Adviser GP or the Adviser is a beneficial owner of such securities for purposes of Section 16 or any other purpose.

SEC source: 0001638599-17-001008 · doc4_5014.xml · nonDerivative · entry 3

BAKER BROS. ADVISORS LP · CIK 0001263508 · Former 10% owner

Baker Bros. Advisors (GP) LLC · CIK 0001580575 · Former 10% owner

BAKER FELIX · CIK 0001087940 · Former 10% owner

BAKER JULIAN · CIK 0001087939 · Former 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 170,778

F4 · shares: On October 5, 2017, 667 and Life Sciences purchased 87,809 and 797,191 shares of common stock of the Issuer at a price of $17.00 per share, respectively, pursuant to an IPO.

F2 · ownership.nature: After giving effect to the transactions reported herein, and as a result of their ownership interest in Baker Biotech Capital (GP), LLC, Julian C. Baker and Felix J. Baker may be deemed to have an indirect pecuniary interest in shares of the Issuer's common stock reported in column 5 of Table I directly held by 667, L.P. ("667"), a limited partnership of which the sole general partner is Baker Biotech Capital, L.P., a limited partnership of which the sole general partner is Baker Biotech Capital (GP), LLC, due to Baker Biotech Capital, L.P.'s right to receive an allocation of a portion of the profits from 667.

F7 · ownership.nature: Baker Bros. Advisors LP (the "Adviser") serves as the Investment Adviser to the Funds. In connection with the services provided by the Adviser, the Adviser receives an asset-based management fee that does not confer any pecuniary interest in the securities held by the Funds. Baker Bros. Advisors (GP) LLC (the "Adviser GP") is the Adviser's sole general partner. Julian C. Baker and Felix J. Baker are principals of the Adviser GP. The Adviser has complete and unlimited discretion and authority with respect to the investment and voting power of the securities held by the Funds.

F8 · ownership.nature: The general partners of the Funds relinquished to the Adviser all discretion and authority with respect to the investment and voting power of the securities held by the Funds. Julian C. Baker, Felix J. Baker, the Adviser GP and the Adviser disclaim beneficial ownership of the securities held directly by the Funds except to the extent of their pecuniary interest therein, and this report shall not be deemed an admission that any of Julian C. Baker, Felix J. Baker, the Adviser GP or the Adviser is a beneficial owner of such securities for purposes of Section 16 or any other purpose.

SEC source: 0001638599-17-001008 · doc4_5014.xml · nonDerivative · entry 2

BAKER BROS. ADVISORS LP · CIK 0001263508 · Former 10% owner

Baker Bros. Advisors (GP) LLC · CIK 0001580575 · Former 10% owner

BAKER FELIX · CIK 0001087940 · Former 10% owner

BAKER JULIAN · CIK 0001087939 · Former 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 1,081,051

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · shares: Represents shares of common stock of Rhythm Pharmaceuticals, Inc. (the "Issuer") received upon conversion of shares of the Issuer's Series A Convertible Preferred Stock ("Series A Preferred") which automatically convert into common stock of the Issuer on a 9.17 for 1 basis (the "Conversion Ratio") without consideration upon the closing of the initial public offering of the Issuer ("IPO").

F1 · price: Represents shares of common stock of Rhythm Pharmaceuticals, Inc. (the "Issuer") received upon conversion of shares of the Issuer's Series A Convertible Preferred Stock ("Series A Preferred") which automatically convert into common stock of the Issuer on a 9.17 for 1 basis (the "Conversion Ratio") without consideration upon the closing of the initial public offering of the Issuer ("IPO").

F3 · ownership.nature: After giving effect to the transactions reported herein, and as a result of their ownership interest in Baker Brothers Life Sciences Capital (GP), LLC, Julian C. Baker and Felix J. Baker may be deemed to have an indirect pecuniary interest in shares of the Issuer's common stock reported in column 5 of Table I directly held by Baker Brothers Life Sciences, L.P. ("Life Sciences" and together with 667, the "Funds"), a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital, L.P., a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital (GP), LLC, due to Baker Brothers Life Sciences Capital, L.P.'s right to receive an allocation of a portion of the profits from Life Sciences.

F7 · ownership.nature: Baker Bros. Advisors LP (the "Adviser") serves as the Investment Adviser to the Funds. In connection with the services provided by the Adviser, the Adviser receives an asset-based management fee that does not confer any pecuniary interest in the securities held by the Funds. Baker Bros. Advisors (GP) LLC (the "Adviser GP") is the Adviser's sole general partner. Julian C. Baker and Felix J. Baker are principals of the Adviser GP. The Adviser has complete and unlimited discretion and authority with respect to the investment and voting power of the securities held by the Funds.

F8 · ownership.nature: The general partners of the Funds relinquished to the Adviser all discretion and authority with respect to the investment and voting power of the securities held by the Funds. Julian C. Baker, Felix J. Baker, the Adviser GP and the Adviser disclaim beneficial ownership of the securities held directly by the Funds except to the extent of their pecuniary interest therein, and this report shall not be deemed an admission that any of Julian C. Baker, Felix J. Baker, the Adviser GP or the Adviser is a beneficial owner of such securities for purposes of Section 16 or any other purpose.

SEC source: 0001638599-17-001008 · doc4_5014.xml · nonDerivative · entry 1

BAKER BROS. ADVISORS LP · CIK 0001263508 · Former 10% owner

Baker Bros. Advisors (GP) LLC · CIK 0001580575 · Former 10% owner

BAKER FELIX · CIK 0001087940 · Former 10% owner

BAKER JULIAN · CIK 0001087939 · Former 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 82,969

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · shares: Represents shares of common stock of Rhythm Pharmaceuticals, Inc. (the "Issuer") received upon conversion of shares of the Issuer's Series A Convertible Preferred Stock ("Series A Preferred") which automatically convert into common stock of the Issuer on a 9.17 for 1 basis (the "Conversion Ratio") without consideration upon the closing of the initial public offering of the Issuer ("IPO").

F1 · price: Represents shares of common stock of Rhythm Pharmaceuticals, Inc. (the "Issuer") received upon conversion of shares of the Issuer's Series A Convertible Preferred Stock ("Series A Preferred") which automatically convert into common stock of the Issuer on a 9.17 for 1 basis (the "Conversion Ratio") without consideration upon the closing of the initial public offering of the Issuer ("IPO").

F2 · ownership.nature: After giving effect to the transactions reported herein, and as a result of their ownership interest in Baker Biotech Capital (GP), LLC, Julian C. Baker and Felix J. Baker may be deemed to have an indirect pecuniary interest in shares of the Issuer's common stock reported in column 5 of Table I directly held by 667, L.P. ("667"), a limited partnership of which the sole general partner is Baker Biotech Capital, L.P., a limited partnership of which the sole general partner is Baker Biotech Capital (GP), LLC, due to Baker Biotech Capital, L.P.'s right to receive an allocation of a portion of the profits from 667.

F7 · ownership.nature: Baker Bros. Advisors LP (the "Adviser") serves as the Investment Adviser to the Funds. In connection with the services provided by the Adviser, the Adviser receives an asset-based management fee that does not confer any pecuniary interest in the securities held by the Funds. Baker Bros. Advisors (GP) LLC (the "Adviser GP") is the Adviser's sole general partner. Julian C. Baker and Felix J. Baker are principals of the Adviser GP. The Adviser has complete and unlimited discretion and authority with respect to the investment and voting power of the securities held by the Funds.

F8 · ownership.nature: The general partners of the Funds relinquished to the Adviser all discretion and authority with respect to the investment and voting power of the securities held by the Funds. Julian C. Baker, Felix J. Baker, the Adviser GP and the Adviser disclaim beneficial ownership of the securities held directly by the Funds except to the extent of their pecuniary interest therein, and this report shall not be deemed an admission that any of Julian C. Baker, Felix J. Baker, the Adviser GP or the Adviser is a beneficial owner of such securities for purposes of Section 16 or any other purpose.

SEC source: 0001209191-17-056611 · doc4.xml · derivative · entry 3

Foley Todd · CIK 0001473930 · Director · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 3,015,915

Underlying: Common Stock · 328,889 shares

Expires not disclosed

F1 · derivative.exercise_price: 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.

F1 · derivative.exercise_date: 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.

F1 · derivative.expiration_date: 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.

F5 · ownership.nature: Shares were purchased as follows: 2,903,134 by BV V and 112,781 by AM BV5.

F6 · ownership.nature: Reflects a transaction with the Issuer prior to its Section 12 registration which occurred within 6 months of of the post-registration transaction reported on this Form 4.