X0206 3 2018-06-20 0 0001681087 AVROBIO, Inc. AVRO 0001628098 Atlas Venture Fund X, L.P. 400 TECHNOLOGY SQUARE, 10TH FLOOR CAMBRIDGE MA 02139 0 0 1 0 0001742766 ATLAS VENTURE ASSOCIATES X, L.P. 400 TECHNOLOGY SQUARE, 10TH FLOOR CAMBRIDGE MA 02139 0 0 1 0 0001742765 Atlas Venture Associates X, LLC 400 TECHNOLOGY SQUARE, 10TH FLOOR CAMBRIDGE MA 02139 0 0 1 0 Series Seed Preferred Stock Common Stock 3333333 I See Footnote Series A Preferred Stock Common Stock 12580199 I See Footnote Series B Preferred Stock Common Stock 3740239 I See Footnote All series of Convertible Preferred Stock shall automatically convert on a 4.132-for-1 basis into shares of the Issuer's Common Stock immediately prior to the closing of the Issuer's initial public offering and have no expiration date The shares are held directly by Atlas Venture Fund X, L.P. ("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. Each of AVA X LP and AVA X LLC disclaims Section 16 beneficial ownership of the securities held by Atlas Venture Fund X, except to the extent of its pecuniary interest therein, if any. Atlas Venture Fund X, LP, By: Atlas Venture Associates X, L.P., it's general partner, By: Atlas Venture Associates X, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan 2018-06-20 Atlas Venture Associates X, LP, By: Atlas Venture Associates X, LLC, it's general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan 2018-06-20 Atlas Venture Associates X, LLC, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan 2018-06-20