X0306 4 2019-05-20 1 0001681087 AVROBIO, Inc. AVRO 0001597143 Clarus Lifesciences III, L.P. C/O CLARUS VENTURES 101 MAIN STREET, SUITE 1210 CAMBRIDGE MA 02142 0 0 1 0 0001620148 Clarus Ventures III GP, L.P. C/O CLARUS VENTURES 101 MAIN STREET, SUITE 1210 CAMBRIDGE MA 02142 0 0 1 0 Common Stock 2019-05-20 4 J 0 1481163 D 1481162 I See Footnotes Represents a distribution of shares of common stock of the issuer (the "Common Stock") previously held directly by Clarus Lifesciences III, L.P. ("Clarus III") to limited partners of Clarus III, including Clarus Ventures III GP, L.P. ("Clarus GP"), in respect of their indirect interests in Clarus III (the "Clarus III Distribution"). Clarus GP then distributed the 202,995 shares of Common Stock it received in the Clarus III Distribution to its limited partners. These securities are held directly by Clarus III. Clarus GP is the sole general partner of Clarus III. Blackstone Clarus III L.L.C. is the sole general partner of Clarus GP. The sole member of Blackstone Clarus III L.L.C. is Blackstone Holdings II L.P. The sole general partner of Blackstone Holdings II L.P. is Blackstone Holdings I/II GP Inc. The controlling shareholder of Blackstone Holdings I/II GP Inc. is The Blackstone Group L.P. The sole general partner of The Blackstone Group L.P. is Blackstone Group Management L.L.C. Blackstone Group Management L.L.C. is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person. Each of the Reporting Persons (other than Clarus III) disclaims beneficial ownership of the securities held by Clarus III, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934, each of the Reporting Persons (other than Clarus III) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the reported securities for purposes of Section 16 or for any other purpose. CLARUS LIFESCIENCES III, L.P., By: Clarus Ventures III GP, L.P., its GP, By: Blackstone Clarus III L.L.C., its GP, By: Blackstone Holdings II L.P., its managing member, By: Blackstone Holdings I/II GP Inc., its GP, By /s/ John G. Finley, Title: CLO 2019-05-22 CLARUS VENTURES III GP, L.P., By: Blackstone Clarus III L.L.C., its GP, By: Blackstone Holdings II L.P., its managing member, By: Blackstone Holdings I/II GP Inc., its GP, By: /s/ John G. Finley, Title: Chief Legal Officer 2019-05-22