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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Name of Issuer)

(Title of Class of Securities)

(CUSIP Number)

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

SCHEDULE 13D/A 0001415889-25-022121 0001628098 XXXXXXXX LIVE 5 Common Stock, $0.0001 par value per share 12/12/2025 false 0001816736 254604101 DISC MEDICINE, INC. 321 ARSENAL STREET, SUITE 101 WATERTOWN MA 02472 Ommer Chohan, CFO (857) 201-2700 Atlas Venture, 300 Technology Square 8th Floor Cambridge MA 02139 0001628098 N Atlas Venture Fund X, L.P. b WC N DE 0.00 813167.00 0.00 813167.00 813167.00 N 2.2 PN 0001742766 N ATLAS VENTURE ASSOCIATES X, L.P. b AF N DE 0.00 813167.00 0.00 813167.00 813167.00 N 2.2 PN 0001742765 N Atlas Venture Associates X, LLC b AF N DE 0.00 813167.00 0.00 813167.00 813167.00 N 2.2 OO 0001812049 N Atlas Venture Fund XII, L.P. b WC N DE 0.00 14013.00 0.00 14013.00 14013.00 N 0.0 PN 0001845875 N Atlas Venture Associates XII, L.P. b AF N DE 0.00 14013.00 0.00 14013.00 14013.00 N 0.0 PN 0001845871 N Atlas Venture Associates XII, LLC b AF N DE 0.00 14013.00 0.00 14013.00 14013.00 N 0.0 OO 0001759241 N Atlas Venture Opportunity Fund I, L.P. b WC N DE 0.00 349210.00 0.00 349210.00 349210.00 N 0.9 PN 0001780065 N Atlas Venture Associates Opportunity I, L.P. b AF N DE 0.00 349210.00 0.00 349210.00 349210.00 N 0.9 PN 0001780066 N Atlas Venture Associates Opportunity I, LLC b AF N DE 0.00 349210.00 0.00 349210.00 349210.00 N 0.9 OO 0001885327 N Atlas Venture Opportunity Fund II, L.P. b WC N DE 0.00 337485.00 0.00 337485.00 337485.00 N 0.9 PN 0001935814 N Atlas Venture Associates Opportunity II, LP b AF N DE 0.00 337485.00 0.00 337485.00 337485.00 N 0.9 PN 0001935810 N Atlas Venture Associates Opportunity II, LLC b AF N DE 0.00 337485.00 0.00 337485.00 337485.00 N 0.9 OO Common Stock, $0.0001 par value per share DISC MEDICINE, INC. 321 ARSENAL STREET, SUITE 101 WATERTOWN MA 02472 This Amendment No. 5 to Schedule 13D ("Amendment No. 5") is being filed as an amendment to the statement on Schedule 13D relating to common stock, par value $0.0001 per share of Disc Medicine, Inc., a Delaware corporation, as filed with the Securities and Exchange Commission (the "SEC") on February 16, 2021 (the "Initial Schedule 13D") and later amended on February 14, 2023 ("Amendment No. 1") , September 21, 2023 ("Amendment No. 2"), January 24, 2024 ("Amendment No. 3"), and August 15, 2025 ("Amendment No. 4") and together with the Initial Schedule 13D, Amendment No. 1, Amendment No. 2 and Amendment No. 3, the "Prior Schedule 13D"). All capitalized terms not otherwise defined herein shall have the meanings ascribed to the terms in the Prior Schedule 13D. The Prior Schedule 13D is hereby amended and supplemented as follows and, except as expressly amended below, the Prior Schedule 13D remains in full force and effect. As of the date hereof, Atlas X is the record owner of 813,167 shares of Common Stock. AVA X LP is the general partner of Atlas X and AVA X LLC is the general partner of AVA X LP. Each of Atlas X, AVA X LP and AVA X LLC has shared voting and dispositive power over the shares held by Atlas X. As such, each of Atlas X, AVA X LP and AVA X LLC may be deemed to beneficially own the shares held by Atlas X. As of the date hereof, Atlas XII is the record owner of 14,013 shares of Common Stock. AVA XII LP is the general partner of Atlas XII and AVA XII LLC is the general partner of AVA XII LP. Each of Atlas XII, AVA XII LP and AVA XII LLC has shared voting and dispositive power over the shares held by Atlas XII. As such, each of Atlas XII, AVA XII LP and AVA XII LLC may be deemed to beneficially own the shares held by Atlas XII. As of the date hereof, AVOF is the record owner of 349,210 shares of Common Stock. AVAO LP is the general partner of AVOF and AVAO LLC is the general partner of AVAO LP. Each of AVOF, AVAO LP and AVAO LLC has shared voting and dispositive power over the shares held by AVOF. As such, each of AVOF, AVAO LP and AVAO LLC may be deemed to beneficially own the shares held by AVOF. As of the date hereof, AVOF II is the record owner of 337,485 shares of Common Stock. AVAO II LP is the general partner of AVOF II and AVAO II LLC is the general partner of AVAO II LP. Each of AVOF II, AVAO II LP and AVAO II LLC has shared voting and dispositive power over the shares held by AVOF II. As such, each of AVOF II, AVAO II LP and AVAO II LLC may be deemed to beneficially own the shares held by AVOF II. Each of the Fund X Reporting Persons, Fund XII Reporting Persons, Opportunity Fund Reporting Persons and Opportunity Fund II Reporting Persons may be deemed to beneficially own 2.2%, 0.0%, 0.9% and 0.9%, respectively, of the Issuer's outstanding Common Stock, which percentages are calculated based upon 37,750,162 shares of Common Stock outstanding as of October 31, 2025, as reported in the Issuer's Quarterly Report for the quarterly period ended September 30, 2025 on Form 10-Q, filed with the Securities and Exchange Commission on November 6, 2025. Collectively, the Reporting Persons beneficially own an aggregate of 1,513,875 shares of Common Stock, which represents an estimated 4.0% of the Issuer's outstanding Common Stock. The Fund X Reporting Persons, Fund XII Reporting Persons, Opportunity Fund Reporting Persons and the Opportunity Fund II Reporting Persons are under common control and as a result, the Reporting Persons may be deemed to be members of a group. However, the Reporting Persons disclaim such group membership, and this Schedule 13D shall not be deemed an admission that the Reporting Persons are members of a group for purposes of Section 13 or for any other purposes. As of the date hereof, each of Atlas X, AVA X LP and AVA X LLC have shared voting power and shared dispositive power over 813,167 shares of Common Stock. As of the date hereof, each of Atlas XII, AVA XII LP and AVA XII LLC have shared voting power and shared dispositive power over 14,013 shares of Common Stock. As of the date hereof, each of AVOF, AVAO LP and AVAO LLC have shared voting power and shared dispositive power over 349,210 shares of Common Stock. As of the date hereof, each of AVOF II, AVAO II LP and AVAO II LLC have shared voting power and shared dispositive power over 337,485 shares of Common Stock. The transactions in the common stock by the Reporting Persons during the past sixty days are set forth in Exhibit 99.1 and are incorporated herein by reference. The Reporting Persons ceased to be the beneficial owners of more than five percent of the common stock on or before October 31, 2025 by virtue of dilution resulting from the Issuer's issuance of additional shares of common stock and not as a result of any transaction by the Reporting Persons. Transactions in Common Stock During the Past Sixty Days Atlas Venture Fund X, L.P. /s/ Ommer Chohan By: Atlas Venture Associates X, L.P., its general partner, By: Atlas Venture Associates X, LLC, its general partner, By: Ommer Chohan, its CFO 12/17/2025 ATLAS VENTURE ASSOCIATES X, L.P. /s/ Ommer Chohan By: Atlas Venture Associates X, LLC, its general partner, By: Ommer Chohan, its CFO 12/17/2025 Atlas Venture Associates X, LLC /s/ Ommer Chohan Ommer Chohan, CFO 12/17/2025 Atlas Venture Fund XII, L.P. /s/ Ommer Chohan By: Atlas Venture Associates XII, L.P., its general partner, By: Atlas Venture Associates XII, LLC, its general partner, By: Ommer Chohan, its CFO 12/17/2025 Atlas Venture Associates XII, L.P. /s/ Ommer Chohan By: Atlas Venture Associates XII, LLC, its general partner, By: Ommer Chohan, its CFO 12/17/2025 Atlas Venture Associates XII, LLC /s/ Ommer Chohan Ommer Chohan, CFO 12/17/2025 Atlas Venture Opportunity Fund I, L.P. /s/ Ommer Chohan By: Atlas Venture Associates Opportunity I, L.P., its G.P., By: Atlas Venture Associates Opportunity I, LLC, its G.P., By: Ommer Chohan, CFO 12/17/2025 Atlas Venture Associates Opportunity I, L.P. /s/ Ommer Chohan By: Atlas Venture Associates Opportunity I, LLC, its General Partner, By: Ommer Chohan, CFO 12/17/2025 Atlas Venture Associates Opportunity I, LLC /s/ Ommer Chohan Ommer Chohan, CFO 12/17/2025 Atlas Venture Opportunity Fund II, L.P. /s/ Ommer Chohan By: Atlas Venture Associates Opportunity II, L.P., its G.P., By: Atlas Venture Associates Opportunity II, LLC, its G.P., By: Ommer Chohan, CFO 12/17/2025 Atlas Venture Associates Opportunity II, LP /s/ Ommer Chohan By: Atlas Venture Associates Opportunity II, LLC, its General Partner, By: Ommer Chohan, CFO 12/17/2025 Atlas Venture Associates Opportunity II, LLC /s/ Ommer Chohan Ommer Chohan, CFO 12/17/2025