SCHEDULE: Atlas Venture Reduces Stake in Disc Medicine Below 5%

Atlas Venture funds have reduced their beneficial ownership in Disc Medicine, Inc. to below 5% primarily due to dilution from new share issuances, alongside recent stock sales.

Summary

• This is Amendment No. 5 to the Schedule 13D filing for Disc Medicine, Inc., regarding beneficial ownership of its Common Stock, $0.0001 par value per share.
• The reporting persons are various Atlas Venture entities, including Atlas Venture Fund X, L.P., Atlas Venture Fund XII, L.P., Atlas Venture Opportunity Fund I, L.P., and Atlas Venture Opportunity Fund II, L.P., along with their respective general partners.
• Collectively, the Reporting Persons beneficially own an aggregate of 1,513,875 shares of Disc Medicine's Common Stock.
• This aggregate ownership represents an estimated 4.0% of Disc Medicine's outstanding Common Stock.
• The percentage is calculated based on 37,750,162 shares of Common Stock outstanding as of October 31, 2025, as reported by Disc Medicine in its Form 10-Q.
• The Reporting Persons ceased to be beneficial owners of more than five percent of the common stock on or before October 31, 2025, primarily due to dilution from Disc Medicine's issuance of additional shares.
• Atlas Venture entities also conducted sales of common stock between December 12, 2025, and December 17, 2025, at weighted average prices ranging from $91.18 to $93.80 per share.

Sentiment

Score: 4

Explanation: The reduction in a significant institutional investor's stake, even if partly due to dilution, combined with active sales, generally indicates a less positive outlook from that investor's perspective, which could be perceived negatively by the market.

Negatives

• Atlas Venture funds collectively reduced their beneficial ownership in Disc Medicine to 4.0% of outstanding common stock, down from over 5%.
• The reporting persons ceased to be beneficial owners of more than 5% of common stock, partly due to dilution and partly due to recent sales.
• Significant sales of common stock by Atlas X, AVOF, AVOF II, and Atlas XII occurred between December 12-17, 2025, totaling 250,000 shares, indicating a reduction in exposure.

Risks

• Reduced institutional ownership by a significant early investor like Atlas Venture may signal a lack of conviction or a strategic portfolio rebalancing, which could be perceived negatively by the market.
• Dilution from new share issuances indicates a growing share count, which can impact per-share metrics and potentially future earnings per share.

Future Outlook

This filing does not contain any explicit forward-looking statements or guidance from Disc Medicine, Inc. It primarily details changes in beneficial ownership by Atlas Venture funds.

Industry Context

This filing reflects a change in an institutional investor's stake in a publicly traded biotechnology company. Such reductions in ownership by venture capital funds are common as portfolio companies mature, go public, or as funds rebalance their portfolios. The mention of dilution suggests Disc Medicine may have engaged in capital-raising activities or issued shares for other strategic purposes, which is typical for development-stage biotech firms requiring significant funding for R&D and clinical trials.

Comparison to Industry Standards

• A venture capital fund reducing its stake below the 5% threshold is a standard event in the lifecycle of a portfolio company, often signaling a transition from active influence or board representation to a more passive investment or eventual exit.
• The dilution mentioned is a common occurrence in the biotech industry, where companies frequently issue new shares to fund expensive research and development, clinical trials, and operational expenses, leading to a larger share count.

Stakeholder Impact

• Shareholders: May view the reduction in Atlas Venture's stake as a negative signal, potentially impacting investor confidence and share price. The increased share count due to dilution could also impact per-share metrics.
• Company (Disc Medicine): The implied capital raise (leading to dilution) provides funds for operations, but the reduced stake by a founding investor might alter board dynamics or strategic influence.

Key Dates

Recommendation

While the reduction in a significant investor's stake and active sales could be seen as a negative signal, the filing primarily reflects a change in ownership structure rather than a fundamental shift in Disc Medicine's operational performance or prospects. The dilution suggests the company has raised capital, which can be positive for its runway. Investors should hold and monitor future company announcements and operational performance rather than reacting solely to this ownership change.

Keywords

Disc Medicine, Atlas Venture, Schedule 13D, beneficial ownership, common stock, dilution, stock sales, institutional investor, SEC filing