Common Stock, $0.0001 par value per share

DISC MEDICINE, INC.

321 ARSENAL STREET, SUITE 101, WATERTOWN, MA, 02472

As of the date hereof, Atlas X is the record owner of 1,084,527 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 51,000 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 592,908 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 420,549 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 3.1%, 0.1%, 1.7% and 1.2%, respectively, of the Issuer's outstanding Common Stock, which percentages are calculated based upon 34,765,581 shares of Common Stock outstanding as of July 31, 2025, as reported in the Issuer's Quarterly Report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 for the quarterly period ended June 30 on Form 10-Q, filed with the Securities and Exchange Commission on August 7, 2025. Collectively, the Reporting Persons beneficially own an aggregate of 2,148,984 shares of Common Stock, which represents an estimated 6.2% 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 1,084,527 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 51,000 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 592,908 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 420,549 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.