X0306 4 2018-06-25 0 0001681087 AVROBIO, Inc. AVRO 0001451612 Booth Bruce C/O AVROBIO, INC. 1 KENDALL SQUARE, BUILDING 300, STE 201 CAMBRIDGE MA 02139 1 0 0 0 Common Stock 2018-06-25 4 C 0 806711 A 806711 I See Footnote Common Stock 2018-06-25 4 C 0 3044579 A 3851290 I See Footnote Common Stock 2018-06-25 4 C 0 905188 A 4756478 I See Footnote Series Seed Preferred Stock 2018-06-25 4 C 0 3333333 0.00 D Common Stock 806711 0 I See footnote Series A Preferred Stock 2018-06-25 4 C 0 12580199 0.00 D Common Stock 3044579 0 I See footnote Series B Preferred Stock 2018-06-25 4 C 0 3740239 0.00 D Common Stock 905188 0 I See footnote Represents the total number of shares of Common Stock received by Atlas Venture Fund X, L.P. ("Atlas Venture Fund X"), upon the conversion of the Issuer's Series Seed Preferred Stock in connection with the closing of the Issuer's initial public offering. The shares are held directly by Atlas Venture Fund X. The general partner of Atlas Venture Fund X is Atlas Venture Associates X, L.P. ("AVA X LP"). Atlas Venture Associates X, LLC ("AVA X LLC") is the general partner of AVA X LP. Dr. Booth is a member of AVA X LLC and disclaims beneficial ownership of such securities held by Atlas Venture Fund X, except to the extent of his pecuniary interest therein, if any. Represents the total number of shares of Common Stock received by Atlas Venture Fund X upon the conversion of the Issuer's Series A Preferred Stock in connection with the closing of the Issuer's initial public offering. Represents the total number of shares of Common Stock received by Atlas Venture Fund X upon the conversion of the Issuer's Series B Preferred Stock in connection with the closing of the Issuer's initial public offering. All series of Convertible Preferred Stock automatically converted into the Issuer's Common Stock on a 4.132-for-1 basis on June 25, 2018 and had no expiration date. /s/ Bruce Booth 2018-06-25