X0508 4 2023-12-12 0 0001816736 Disc Medicine, Inc. IRON 0001628098 Atlas Venture Fund X, L.P. 300 TECHNOLOGY SQUARE, 8TH FLOOR CAMBRIDGE MA 02139 0 0 1 0 0001742766 ATLAS VENTURE ASSOCIATES X, L.P. 300 TECHNOLOGY SQUARE, 8TH FLOOR CAMBRIDGE MA 02139 0 0 1 0 0001742765 Atlas Venture Associates X, LLC 300 TECHNOLOGY SQUARE, 8TH FLOOR CAMBRIDGE MA 02139 0 0 1 0 0001759241 Atlas Venture Opportunity Fund I, L.P. 300 TECHNOLOGY SQUARE, 8TH FLOOR CAMBRIDGE MA 02139 0 0 1 0 0001780065 Atlas Venture Associates Opportunity I, L.P. 300 TECHNOLOGY SQUARE, 8TH FLOOR CAMBRIDGE MA 02139 0 0 1 0 0001780066 Atlas Venture Associates Opportunity I, LLC 300 TECHNOLOGY SQUARE, 8TH FLOOR CAMBRIDGE MA 0 0 1 0 0 Common Stock 2023-12-12 4 S 0 31235 59.87 D 1562550 D Common Stock 2023-12-12 4 S 0 20823 59.87 D 861401 I See footnote Common Stock 2023-12-12 4 S 0 632 60.99 D 1561918 D Common Stock 2023-12-12 4 S 0 422 60.99 D 860979 I See footnote Common Stock 2023-12-12 4 S 0 6234 62.42 D 1555684 D Common Stock 2023-12-12 4 S 0 4155 62.42 D 856824 I See footnote Common Stock 2023-12-12 4 S 0 994 62.90 D 1554690 D Common Stock 2023-12-12 4 S 0 665 62.90 D 856159 I See footnote Common Stock 2023-12-12 4 S 0 1031 63.78 D 1553659 D Common Stock 2023-12-12 4 S 0 688 63.78 D 855471 I See footnote Common Stock 2023-12-12 4 S 0 27924 65.10 D 1525735 D Common Stock 2023-12-12 4 S 0 18615 65.10 D 836856 I See footnote Common Stock 2023-12-12 4 S 0 9901 65.77 D 1515834 D Common Stock 2023-12-12 4 S 0 6599 65.77 D 830257 I See footnote Common Stock 2023-12-13 4 S 0 5263 59.99 D 1510571 D Common Stock 2023-12-13 4 S 0 3508 59.99 D 826749 I See footnote Common Stock 2023-12-13 4 S 0 60 60.50 D 1510511 D Common Stock 2023-12-13 4 S 0 40 60.50 D 826709 I See footnote Common Stock 2023-12-14 4 S 0 30645 58.27 D 1479866 D Common Stock 2023-12-14 4 S 0 20429 58.27 D 806280 I See footnote Common Stock 2023-12-14 4 S 0 180 59.74 D 1479686 D Common Stock 2023-12-14 4 S 0 120 59.74 D 806160 I See footnote The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $59.50 to $60.497 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnotes (1), (4), (5), (6), (7), (8), (9), (10), (11) and (12). These shares are held directly by Atlas Venture Fund X, L.P. ("Atlas X"). Atlas Venture Associates X, L.P. ("Associates X") is the general partner of Atlas X. Atlas Venture Associates X, LLC ("Associates X LLC") is the general partner of Associates X. Each of Associates X and Associates X LLC disclaims Section 16 beneficial ownership of the securities held by Atlas X, except to the extent of its pecuniary interest therein, if any. These shares are held directly by Atlas Venture Opportunity Fund I, L.P. ("Atlas Opportunity I"). Atlas Venture Associates Opportunity I, L.P. ("Associates I") is the general partner of Atlas Opportunity I. Atlas Venture Associates Opportunity I, LLC ("Associates I LLC") is the general partner of Associates I. Each of Associates I and Associates I LLC disclaims Section 16 beneficial ownership of the securities held by Atlas Opportunity I, except to the extent of its pecuniary interest therein, if any. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $60.51 to $61.50 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $61.5297 to $62.5175 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $62.6436 to $63.3256 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $63.70 to $64.67 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $64.7499 to $65.735 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $65.745 to $66.32 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $59.50 to $60.4381 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $58.25 to $58.65 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $59.53 to $60.17 inclusive. Atlas Venture Fund X, L.P., By: Atlas Venture Associates X, L.P., its general partner, By: Atlas Venture Associates X, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer /s/ Ommer Chohan 2023-12-14 Atlas Venture Associates X, L.P., By: Atlas Venture Associates X, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer /s/ Ommer Chohan 2023-12-14 Atlas Venture Associates X, LLC By: Ommer Chohan, Chief Financial Officer /s/ Ommer Chohan 2023-12-14 Atlas Venture Opportunity Fund I, L.P., By: Atlas Venture Associates Opportunity I, L.P., its general partner, By: Atlas Venture Associates Opportunity I, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer /s/ Ommer Chohan 2023-12-14 Atlas Venture Associates Opportunity I, L.P., By: Atlas Venture Associates Opportunity I, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer /s/ Ommer Chohan 2023-12-14 Atlas Venture Associates Opportunity I, LLC By: Ommer Chohan, Chief Financial Officer /s/ Ommer Chohan 2023-12-14