Atrium Therapeutics filings document the corporate transition that created the current RNA issuer and the related Avidity Biosciences merger, separation and listing records. The filing set includes 8-K material-event reports, shareholder voting disclosures, separation and merger agreement records, capital-structure information and a Form 25 covering removal of Avidity common stock from Nasdaq listing and registration.
Regulatory disclosures tied to the symbol also cover governance matters, operating and financial results, clinical or regulatory updates and security-structure information. As an independent biopharmaceutical company, Atrium's filings center on its RNA therapeutics platform, precision cardiology pipeline, collaboration economics, equity compensation and public-company reporting obligations.
Atrium Therapeutics, Inc. (RNA) reported that Chief Financial Officer Brendan R. Winslow had 6,742 shares of common stock withheld on September 18, 2026 to satisfy tax withholding obligations upon vesting of restricted stock units. The shares were treated as a disposition and his directly held stake is now 36,859 shares. No Rule 10b5-1 trading plan is reported.
Atrium Therapeutics, Inc. (RNA) reported that Chief Strategy Officer Rocio Martin Hoyos had 8,320 shares of common stock withheld on September 18, 2026 to satisfy tax withholding obligations upon the vesting of restricted stock units. The shares were treated as a disposition at a reference price of $8.95 per share, and Hoyos now holds 38,340 common shares directly. No Rule 10b5-1 trading plan is reported for this transaction.
Atrium Therapeutics, Inc. received an updated Schedule 13G/A from RA Capital Management, L.P., Peter Kolchinsky, Rajeev Shah, and RA Capital Healthcare Fund, L.P. reporting that, as of June 30, 2026, they beneficially owned 0 shares of Atrium Therapeutics common stock, representing 0.0% of the class. The filing shows no sole or shared voting or dispositive power over any Atrium shares and indicates that each reporting person now has ownership of 5 percent or less of the common stock.
Sessa Capital IM, L.P. and John Petry report beneficial ownership of common stock of Atrium Therapeutics, Inc. They report beneficial ownership of 1,500,000 shares of common stock, representing 8.8% of the class, based on 17,105,643 shares outstanding as of May 5, 2026 as reported by the company. Voting and dispositive power over these shares is described as shared, with no sole voting or dispositive power reported. The shares are held by certain Sessa funds for which Sessa Capital IM, L.P. acts as investment manager, and Sessa Capital (Master), L.P. is identified as having the right to receive dividends or sale proceeds from more than 5% of the company’s common stock.
T. Rowe Price Associates, Inc. filed an amended Schedule 13G reporting beneficial ownership of 1,472,984 shares of Atrium Therapeutics Inc. common stock, representing 8.6% of the class. It reports sole voting power over 1,472,772 shares and sole dispositive power over 1,472,984 shares, with no shared voting or dispositive power.
The filer states that this report should not be construed as an admission that it is the beneficial owner of these securities, and such beneficial ownership is expressly denied.
Atrium Therapeutics, Inc. is a newly spun‑off, clinical‑stage biotech developing RNA therapeutics targeting cardiomyopathies. For the six months ended June 30, 2026, it generated $22.6 million in collaboration revenue, mainly from a Bristol Myers Squibb milestone, but recorded a net loss of $36.8 million as R&D and G&A spending ramped up post‑separation.
Cash, cash equivalents and short‑term investments totaled $263.9 million, with total assets of $280.5 million and deferred revenue of $42.7 million, providing funding for at least 12 months. The pipeline is led by ATR 1072 for PRKAG2 syndrome (FDA IND cleared, first enrollment expected by end of 2026) and ATR 1086 for PLN cardiomyopathy (IND filing planned in 2027), alongside two earlier cardiology programs.
The company operates as a single segment, continues to recognize revenue under its BMS collaboration, and in August 2026 became entitled to an additional $15.0 million BMS milestone. It remains pre‑commercial and expects continued operating losses as it advances clinical and manufacturing activities and builds public‑company infrastructure.
Atrium Therapeutics reported second-quarter 2026 results and highlighted key R&D milestones. The company received FDA IND clearance for ATR 1072 for PRKAG2 syndrome and initiated Corventis, its first Phase 1/2 clinical trial and first clinical study targeting this disease. Atrium also achieved a second milestone payment under its global cardiovascular collaboration with Bristol Myers Squibb.
For the quarter ended June 30, 2026, Atrium generated $3.0 million in collaboration revenue and recorded a net loss of about $20.2 million, or $1.18 per share. For the first six months of 2026, collaboration revenue was $22.6 million, while the net loss totaled approximately $36.8 million. Operating expenses reflect continued investment in R&D and company build-out.
As of June 30, 2026, Atrium reported $72.3 million in cash and cash equivalents and $191.6 million in short-term investments, supporting its precision cardiology pipeline, including ATR 1072, ATR 1086 for PLN cardiomyopathy, and additional rare cardiomyopathy programs.
BlackRock, Inc. reports beneficial ownership of common stock of Atrium Therapeutics, Inc. in this amended ownership filing. BlackRock reports beneficial ownership of 1,135,757 shares of common stock, representing 6.6% of the class.
BlackRock has sole voting power over 1,119,668 shares and sole dispositive power over all 1,135,757 shares, with no shared voting or dispositive power. Various underlying clients have rights to dividends and sale proceeds, but no single client holds more than five percent of Atrium Therapeutics’ outstanding common shares.
Atrium Therapeutics announced that the U.S. Food and Drug Administration cleared its Investigational New Drug application for ATR 1072, enabling initiation of the Corventis Phase 1/2 trial in PRKAG2 syndrome.
Corventis is an open-label, multicenter study enrolling approximately 37 participants, with multiple ascending dose cohorts followed by an expansion cohort at a recommended Phase 2 dose. The company expects first enrollment by the end of 2026 and initial proof-of-concept data in the second half of 2027. ATR 1072 uses small interfering RNA to silence mutant PRKAG2 messenger RNA with the goal of normalizing AMPK activity and reducing glycogen accumulation in this rare cardiomyopathy, which is estimated to affect 1,000–2,000 people in the U.S.
Atrium Therapeutics Schedule 13G discloses passive holdings by RA Capital and affiliates. The filing reports that RA Capital Healthcare Fund, L.P. directly holds 864,102 shares of Common Stock, representing 5.6% of the class based on 15,514,996 shares outstanding as of February 26, 2026. The filing explains that RA Capital serves as investment adviser and that voting and dispositive power over the Fund's shares are delegated to RA Capital; the Reporting Persons disclaim group status and disclaim beneficial ownership except as required for Section 13(d) purposes.