SCHEDULE: ADAR1 Capital Discloses 2.7% Stake in Prothena

ADAR1 Capital Management, along with its affiliates and manager Daniel Schneeberger, reported a beneficial ownership of 2.7% in Prothena Corporation Public Limited Company as of September 30, 2025.

Summary

• ADAR1 Capital Management, LLC, ADAR1 Capital Management GP, LLC, and Daniel Schneeberger collectively reported beneficial ownership of Prothena Corporation Public Limited Company.
• As of September 30, 2025, ADAR1 Capital Management, LLC and Daniel Schneeberger beneficially owned 1,469,098 Ordinary Shares, representing 2.7% of the class.
• ADAR1 Capital Management GP, LLC beneficially owned 1,189,587 Ordinary Shares, representing 2.2% of the class.
• The ownership is primarily held through ADAR1 Partners, LP, Spearhead Insurance Solutions IDF, LLC, and other separately managed accounts.
• The filing is an Amendment No. 1 to a Schedule 13G, indicating a previous filing existed.
• The total outstanding Ordinary Shares of Prothena Corporation Public Limited Company used for calculation was 53,829,982 as of September 30, 2025.

Sentiment

Score: 5

Explanation: The filing is a routine disclosure of beneficial ownership, providing factual information without inherent positive or negative sentiment regarding the issuer's performance or prospects. The statement that shares were acquired in the ordinary course of business and not for control purposes maintains a neutral stance.

Positives

• The disclosure of an investment firm's stake can signal institutional interest in Prothena Corporation.
• The investment is stated to be acquired and held in the ordinary course of business and not for the purpose of changing or influencing control of the issuer.

Future Outlook

NA

Industry Context

This filing indicates that an investment management firm, ADAR1 Capital Management, and its principals maintain a significant, though non-controlling, investment in Prothena Corporation, a publicly traded company. Such disclosures are routine for institutional investors and provide transparency into their portfolio holdings.

Stakeholder Impact

• Shareholders: Provides transparency regarding institutional ownership, potentially signaling confidence from an investment firm.
• Management: Awareness of a significant institutional shareholder.

Key Dates

Keywords

Prothena Corporation, ADAR1 Capital Management, Daniel Schneeberger, Schedule 13G, beneficial ownership, investment adviser, ordinary shares, institutional investment