X0306 4 2019-07-19 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 Common Stock 2019-07-19 4 P 0 810811 18.50 A 5567289 I See Footnote 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, L.P., By: Atlas Venture Associates X, L.P., its general partner, By: Atlas Associates X, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan 2019-07-23 Atlas Venture Associates X, L.P., By: Atlas Venture Associates X, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan 2019-07-23 Atlas Venture Associates X, LLC, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan 2019-07-23