Atrium Therapeutics reverses heart glycogen buildup in mice
Atrium’s presentation lists an anticipated 2027 IND filing for ATR 1086, its investigational candidate for PLN cardiomyopathy.
Sentiment and the balance of points
Rhea-AI Sentiment reads the wording of the document, how positive or negative its language is on a 1 to 5 scale. The balance of points shown with the takes weighs what the document actually discloses, so the two can disagree, for example when a trial that missed its main goal is described in upbeat language.
Rhea-AI Filing Summary
Atrium Therapeutics, Inc. (RNA) said it will present nonclinical results for ATR 1072, its investigational PRKAG2 syndrome therapy, on November 6, 2026, at HCMS during the American Heart Association Scientific Sessions. In a company-developed mouse model, mice received one dose of mATR 1072, a mouse surrogate, after disease features had been established for three weeks. Four weeks after treatment, cardiac glycogen accumulation was reversed, while cardiac hypertrophy and ECG parameters improved.
Corventis is a Phase 1/2 open-label trial that will enroll approximately 37 participants. Atrium expects initial proof-of-concept data in the second half of 2027. The trial’s primary endpoint is treatment-emergent adverse events; secondary measures include PRKAG2 mRNA reduction and siRNA tissue concentrations.
The corporate presentation lists $264 million in cash, cash equivalents and investments as of June 30, 2026, with runway through the end of 2028. That runway excludes the $15 million milestone earned from Bristol Myers Squibb, announced August 13, 2026, and proceeds from the $50 million private placement announced October 8, 2026. It also lists $1.5 billion in potential R&D milestone payments from existing BMS and LLY collaborations, subject to the agreements’ terms and conditions.
Filing Explained
The updated presentation reports that Corventis has dosed its first participant, moving ATR 1072 into human testing; the Phase 1/2 trial is designed to evaluate safety, tolerability, pharmacokinetics, pharmacodynamics and efficacy.
8-K Event Classification
Key Figures
Key Terms
surrogate technical
treatment-emergent adverse events medical
pharmacokinetics medical
siRNA technical
FAQ
AI-generated questions and answers. How Rhea-AI works. Not financial advice.
What did ATR 1072 show in RNA’s PRKAG2 mouse study?
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AI-generated analysis. How Rhea-AI works. Not financial advice.
UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
FORM
CURRENT REPORT
Pursuant to Section 13 OR 15(d)
of The Securities Exchange Act of 1934
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Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).
Emerging growth company
If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.
| Item 7.01 | Regulation FD Disclosure. |
On November 2, 2026, Atrium Therapeutics, Inc. (the “Company”) issued a press release regarding its upcoming poster presentation on November 6, 2026 at the Hypertrophic Cardiomyopathy Medical Society (“HCMS”) at the American Heart Association Scientific Sessions 2026. A copy of the press release is attached as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated by reference into this Item 7.01.
The Company has also updated its corporate presentation as of November 2, 2026. The Company’s corporate presentation will be posted on the Investors/Media page under the Investors section of the Company’s website. A copy of the corporate presentation is attached as Exhibit 99.2 to this Current Report on Form 8-K and is incorporated by reference into this Item 7.01.
The information contained in this Item 7.01, including in Exhibit 99.1 and Exhibit 99.2 hereto, is being “furnished” and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), is not subject to the liabilities of that section and shall not be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific reference in such a filing.
| Item 8.01 | Other Events. |
On November 2, 2026, the Company announced that it will present new nonclinical data supporting its lead investigational therapy ATR 1072 for the potential treatment of Protein Kinase AMP-activated non-catalytic subunit Gamma 2 (“PRKAG2”) syndrome during HCMS at the American Heart Association Scientific Sessions 2026, taking place on November 6, 2026, in Chicago, Illinois.
The nonclinical results being presented at HCMS were generated in a new mouse model of PRKAG2 syndrome developed by the Company that demonstrates key features of the disease, including cardiac glycogen accumulation, cardiac hypertrophy, and electrocardiogram (“ECG”) abnormalities. In the study, mice received a single dose of mATR 1072, a mouse surrogate of ATR 1072, after features of the disease had been established for three weeks. By targeting disease causing variant PRKAG2 mRNA in the heart, mATR 1072 treatment led to reversal of cardiac glycogen accumulation as well as improvement in other key features of the disease, including hypertrophy and ECG parameters.
Forward-Looking Statements
This report contains forward-looking statements within the meaning of the United States Private Securities Litigation Reform Act of 1995. Forward-looking statements can generally be identified by words such as “potential,” “can,” “will,” “plan,” “may,” “could,” “would,” “expect,” “anticipate,” “look forward,” “believe,” “committed,” “investigational,” “pipeline,” “ designed to, “ “ target, “ “continue,” “encouraged,” “support,” or similar terms, or by express or implied discussions regarding Atrium Therapeutics’ (“Atrium’s” “we” or “our”) product candidates, nonclinical studies, clinical trials and future results of operations and financial condition. Specifically, this report contains forward-looking information relating to our planned presentation of nonclinical data at the HCMS Scientific Sessions 2026; the extent to which our new nonclinical model is representative of human PRKAG2 syndrome, and the extent to which nonclinical results observed with mATR1072, a mouse surrogate of ATR 1072, support the scientific rationale for ATR 1072 or may be predictive of results in humans; the design, conduct, enrollment and anticipated progress of the Corventis Phase 1/2 clinical trial, including the expected number of participants; the therapeutic potential of ATR 1072, including its potential to address the underlying genetic cause of PRKAG2 syndrome; the potential of our targeted RNA delivery platform, including its potential to deliver siRNA to the heart and to overcome challenges associated with non-specific tissue delivery; our estimates of the prevalence of PRKAG2 syndrome; the potential implications of Corventis for the treatment of genetic cardiomyopathies; and the advancement of our pipeline, including ATR 1086 and our research programs. Such forward-looking statements are based on management’s current beliefs and expectations regarding future events, and are subject to significant known and unknown risks and uncertainties. Particular areas where risks or uncertainties could cause our actual results to be materially different than those expressed in our forward-looking statements include but are not limited to: the initiation, timing, progress, and results of our research and development programs, nonclinical studies and clinical trials, including Corventis, and the timing and outcome of our regulatory submissions and interactions with regulatory authorities; the potential for clinical trial results to differ from our nonclinical studies, including results observed in animal models of disease and with surrogate molecules; the risk that initial, interim or preliminary data from our clinical trials, including Corventis, may change as more participant data become available and may not be predictive of final results; the occurrence of adverse events or other unexpected safety findings, which could result in clinical holds or the delay or discontinuation of development; our ability to identify and timely enroll a sufficient number of participants in our clinical trials, including Corventis, particularly in light of the rarity of the diseases we are targeting; the beneficial characteristics, including potential safety, efficacy and therapeutic effects of our product candidates and the potential advantages of our product candidates compared to alternative therapies; the success and capabilities of the RNA delivery platform; the prevalence of certain diseases and conditions we
intend to treat and our estimates of the potential market opportunity for our product candidates; the timing of and costs involved in obtaining and maintaining regulatory approval of our current and any future product candidates; our ability to develop our current and future product candidates; the implementation of our strategic plans for our business, product candidates, research programs and technologies; developments related to our competitors and our industry; our competitive position and the success of competing therapies that are or may become available; our ability to maintain our current license agreements and collaborations and identify and enter into future license agreements and collaborations; the expected potential benefits of strategic collaborations with third parties and our ability to attract collaborators in the future; our reliance on third parties for manufacturing and to conduct nonclinical studies and clinical trials of our product candidates; our ability to efficiently and cost-effectively conduct our current and future trials; the costs of operating as a public Company; the accuracy of our estimates regarding future expenses, future revenue, capital requirements and the need for additional financing; the period over which we estimate our existing cash and cash equivalents will be sufficient to fund our future operating expenses and capital expenditure requirements; and other factors specified under the heading “Risk Factors” in Atrium’s Quarterly Reports on Form 10-Q for the quarters ended March 31, 2026 and June 30, 2026 filed with the SEC and in other filings and furnishings made by Atrium with the SEC from time to time, which are all available on the SEC’s website at www.sec.gov. Atrium is providing the information in this report as of this date and does not undertake any obligation to update any forward-looking statements contained in this report as a result of new information, future events or otherwise, except as required by law.
| Item 9.01 | Financial Statements and Exhibits. |
(d) Exhibits
| 99.1 | Press Release, dated November 2, 2026 | |
| 99.2 | Corporate Presentation, November 2, 2026 | |
| 104 | Cover Page Interactive Data File (embedded within the Inline XBRL document) | |
SIGNATURES
Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.
| ATRIUM THERAPEUTICS, INC. | ||||||
| Date: November 2, 2026 | By: | /s/ Kathleen Gallagher | ||||
| Name: | Kathleen Gallagher | |||||
| Title: | Chief Executive Officer | |||||
Exhibit 99.1
Atrium Therapeutics to Present Nonclinical Data Showing ATR 1072
Reversed and Improved Features of PRKAG2 Syndrome During HCMS
at AHA Scientific Sessions 2026
— ATR 1072 impacted key characteristics of PRKAG2 syndrome, including accumulation of
cardiac glycogen and cardiac hypertrophy —
— Data further reinforce scientific rationale for ATR 1072 targeting the root cause of
PRKAG2 syndrome —
— Poster presentation November 6 at 5:30 p.m. CT —
SAN DIEGO, Nov. 2, 2026 – Atrium Therapeutics, Inc. (Nasdaq: RNA) (the “Company”), a biopharmaceutical company advancing precision cardiology by developing RNA therapeutics targeted to the heart, today announced that it will present new nonclinical data supporting its lead investigational therapy ATR 1072 for the potential treatment of PRKAG2 (Protein Kinase AMP-activated non-catalytic subunit Gamma 2) syndrome during Hypertrophic Cardiomyopathy Medical Society at the American Heart Association Scientific Sessions 2026, taking place on November 6, 2026, in Chicago, Illinois.
“Our new nonclinical model reproduced many features of PRKAG2 syndrome, including cardiac glycogen accumulation in the heart,” said Husam Younis, Chief Scientific Officer of Atrium Therapeutics. “We are encouraged to see that a mouse-specific version of ATR 1072 reversed cardiac glycogen accumulation and improved other key features of the disease. These findings continue to strengthen the scientific rationale for ATR 1072. We now look to the ongoing Phase 1/2 Corventis trial and expect initial proof of concept data in the second half of 2027.”
The nonclinical results being presented at HCMS were generated in a new mouse model of PRKAG2 syndrome developed by Atrium that demonstrates key features of the disease, including cardiac glycogen accumulation, cardiac hypertrophy, and electrocardiogram (ECG) abnormalities. In the study, mice received a single dose of mATR 1072, a mouse surrogate of ATR 1072, after features of the disease had been established for three weeks. By targeting disease causing variant PRKAG2 mRNA in the heart, mATR 1072 treatment led to reversal of cardiac glycogen accumulation as well as improvement in other key features of the disease, including hypertrophy and ECG parameters.
Details of the HCMS Scientific Sessions poster:
Friday, November 6, 2026, at 5:30 p.m CT.
Targeting PRKAG2 mRNA with mATR 1072 to improve glycogen-storage cardiomyopathy in a mouse model of PRKAG2 syndrome
Presentation Number: HCM32; Poster Board Number: 32
About PRKAG2 Syndrome
PRKAG2 syndrome is a rare, autosomal dominant, early-onset cardiomyopathy caused by variants in the PRKAG2 gene, which encodes the Gamma 2 regulatory subunit of AMPK. Variants enhance AMPK activity leading to abnormal glycogen accumulation in the heart, thickened heart muscles, electrical conduction problems, and arrhythmias. Based on current scientific literature estimates, there are at least 1,000 – 2,000 people with PRKAG2 syndrome in the US. Current management is limited to symptomatic treatment; no approved therapies exist to address the underlying genetic driver of disease.
About the Corventis™ Trial
Corventis™ is a Phase 1/2 open-label, multicenter clinical trial designed to evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics, and efficacy of ATR 1072 in participants living with PRKAG2 syndrome. The study will enroll approximately 37 participants across two parts: Part A, multiple ascending dose cohorts to characterize safety and support dose selection, and Part B, a single-arm expansion cohort at the recommended Phase 2 dose to further evaluate efficacy trends in cardiac structure and function. The study’s primary endpoint is the incidence of treatment-emergent adverse events, with secondary and exploratory endpoints such as PRKAG2 mRNA reduction, siRNA tissue concentrations and plasma pharmacokinetics.
Additional information about the trial is available at www.corventistrial.com.
About Atrium Therapeutics
Atrium Therapeutics, Inc. (Nasdaq: RNA) is pioneering targeted delivery of ribonucleic acid (RNA) therapeutics to the heart to transform the standard of care for people living with cardiomyopathies. The Company’s proprietary technology—designed at Avidity Biosciences, Inc. - combines the tissue selectivity of monoclonal antibodies (mAbs) and other targeted delivery ligands with the precision of oligonucleotides and is designed to
selectively target the underlying drivers of genetically driven cardiac diseases through targeted, non-viral delivery of small interfering RNA (siRNA). This approach builds upon learnings from demonstrated delivery to skeletal muscle and applies it for efficient delivery to the heart, with the potential to overcome challenges associated with non-specific tissue delivery. The Company’s pipeline includes ATR 1072 for PRKAG2 syndrome, ATR 1086 for PLN (phospholamban) cardiomyopathy and two undisclosed research targets in rare cardiomyopathies.
For more information about our RNA delivery platform, development pipeline and people, please visit https://atriumtherapeutics.com/ and engage with us on LinkedIn.
Forward-Looking Statements
This press release contains forward-looking statements within the meaning of the United States Private Securities Litigation Reform Act of 1995. Forward-looking statements can generally be identified by words such as “potential,” “can,” “will,” “plan,” “may,” “could,” “would,” “expect,” “anticipate,” “look forward,” “believe,” “committed,” “investigational,” “pipeline,” “ designed to, “ “ target, “ “continue,” “encouraged,” “support,” or similar terms, or by express or implied discussions regarding Atrium Therapeutics’ (“Atrium’s” “we” or “our”) product candidates, nonclinical studies, clinical trials and future results of operations and financial condition. Specifically, this press release contains forward-looking information relating to our planned presentation of nonclinical data at the HCMS Scientific Sessions 2026; the extent to which our new nonclinical model is representative of human PRKAG2 syndrome, and the extent to which nonclinical results observed with mATR1072, a mouse surrogate of ATR 1072, support the scientific rationale for ATR 1072 or may be predictive of results in humans; the design, conduct, enrollment and anticipated progress of the Corventis Phase 1/2 clinical trial, including the expected number of participants; the therapeutic potential of ATR 1072, including its potential to address the underlying genetic cause of PRKAG2 syndrome; the potential of our targeted RNA delivery platform, including its potential to deliver siRNA to the heart and to overcome challenges associated with non-specific tissue delivery; our estimates of the prevalence of PRKAG2 syndrome; the potential implications of Corventis for the treatment of genetic cardiomyopathies; and the advancement of our pipeline, including ATR 1086 and our research programs. Such forward-looking statements are based on management’s current beliefs and expectations regarding future events, and are subject to significant known and unknown risks and uncertainties. Particular areas where risks or uncertainties could cause
our actual results to be materially different than those expressed in our forward-looking statements include but are not limited to: the initiation, timing, progress, and results of our research and development programs, nonclinical studies and clinical trials, including Corventis, and the timing and outcome of our regulatory submissions and interactions with regulatory authorities; the potential for clinical trial results to differ from our nonclinical studies, including results observed in animal models of disease and with surrogate molecules; the risk that initial, interim or preliminary data from our clinical trials, including Corventis, may change as more participant data become available and may not be predictive of final results; the occurrence of adverse events or other unexpected safety findings, which could result in clinical holds or the delay or discontinuation of development; our ability to identify and timely enroll a sufficient number of participants in our clinical trials, including Corventis, particularly in light of the rarity of the diseases we are targeting; the beneficial characteristics, including potential safety, efficacy and therapeutic effects of our product candidates and the potential advantages of our product candidates compared to alternative therapies; the success and capabilities of the RNA delivery platform; the prevalence of certain diseases and conditions we intend to treat and our estimates of the potential market opportunity for our product candidates; the timing of and costs involved in obtaining and maintaining regulatory approval of our current and any future product candidates; our ability to develop our current and future product candidates; the implementation of our strategic plans for our business, product candidates, research programs and technologies; developments related to our competitors and our industry; our competitive position and the success of competing therapies that are or may become available; our ability to maintain our current license agreements and collaborations and identify and enter into future license agreements and collaborations; the expected potential benefits of strategic collaborations with third parties and our ability to attract collaborators in the future; our reliance on third parties for manufacturing and to conduct nonclinical studies and clinical trials of our product candidates; our ability to efficiently and cost-effectively conduct our current and future trials; the costs of operating as a public Company; the accuracy of our estimates regarding future expenses, future revenue, capital requirements and the need for additional financing; the period over which we estimate our existing cash and cash equivalents will be sufficient to fund our future operating expenses and capital expenditure requirements; and other factors specified under the heading “Risk Factors” in Atrium’s Quarterly Reports on Form 10-Q for the quarters ended March 31, 2026 and June 30, 2026 filed with the SEC and in other filings and furnishings made by Atrium with the SEC from time to time, which are all available on the SEC’s website at www.sec.gov. Atrium is providing the information in this communication as of this date and does not undertake any obligation to update any forward-looking statements contained in this communication as a result of new information, future events or otherwise, except as required by law.
For further information: Investor Relations and Media Contact: Stephanie Kenney, Chief Corporate Affairs Officer, investors@atrium-tx.com
Exhibit 99.2 Atrium Therapeutics 2 November 2026 RNA L I S T E D www.atriumtherapeutics.com NASDAQ 1
Forward-Looking Statements Forward - Looking Statements FORWARD LOOKING STATEMENTS AND OTHER INFORMATION: Certain statements in this Presentation may constitute “forward -looking statem ents” for purposes of the federal securities laws. Our forward -looking statements include, but are not limited to, statements regarding our future results of operations and financial position, including our exp ected cash runway; business strategies and plans; research and development plans, including the anticipated timing of initiating IND -enabling studies and of nominating additional development candidates; the anticipated timin g, costs, design, dosing, enrollment, number and location of trial sites and conduct of our ongoing and planned preclinical studies and clinical trials for our product candidates; the timing of the reporting of data from our clin ical trials, the timing and likelihood of regulatory filings and approvals for our product candidates, the timing and likelihood of success of our research and development programs, plans and objectives of management for future operations and future results of anticipated product development efforts; the design, capability and scalability of our AOC platform, including its ability to efficiently deliver to cardiac tissue and to directly target pathogenic RNA across mul tiple genetically defined cardiomyopathies; the therapeutic potential of our product candidates, including their potential to modify disease progression and the potential of ATR 1072 to address PRKAG2 Syndrome; the extent to which results observed in our nonclinical studies, including studies using surrogate molecules in nonclinical models, may be predictive of results in humans; the potential for modulating calcium cycling to improve diastolic function in cardiom yop athies; our ability to expand into additional indications; our estimates of disease prevalence and market opportunity and identification of higher disease prevalence; and the potential receipt of milestone payments under our collab orations. The forward -looking statements contained in this Presentation are based on our current expectations and beliefs concerning future developments and their potential effects on us. There can be no assurance that fut ure developments affecting us will be those that we have anticipated. These forward -looking statements involve a number of risks, uncertainties (some of which are beyond our control) or other assumptions that may cause actual re sults or performance to be materially different from those expressed or implied by these forward -looking statements including, but not limited to: the initiation, timing, progress, potential registrational quality, and results of our research and development programs, pre clinical studies, any clinical trials, Investigational New Drug Application, and other regulatory submissions; our ability to identify and nominate additional development candidates on our anticipated t imeline or at all; the beneficial characteristics, including potential safety, efficacy and therapeutic effects of our product candidates and the potential advantages of our product candidates compared to alternative therapies; the potentia l for clinical trial results to differ from the results of our nonclinical studies, including data from animal models and from studies using surrogate molecules; the limitations of nonclinical models, which may not fully replicate human disease; the success and capabilities of the RNA delivery platform, including its ability to efficiently deliver to cardiac tissue; the prevalence of certain diseases and conditions we intend to treat and our estimates of the potential ma rket opportunity for our product candidates; the number of patients that we will enroll in our clinical trials and the number and location of trial sites; the timing of and costs involved in obtaining and maintaining regulatory approval of our current product candidates and any future product candidates that we may identify or develop; our ability to meet future regulatory standards with respect to our product candidates, if approved; our plans relating to the further de velopment and manufacturing of our product candidates, including for additional indications that we may pursue; the rate and degree of market acceptance and therapeutic benefits of our product candidates, if approved; our ability to develop or partner and progress our current and future product candidates; the implementation of our strategic plans for our business, product candidates, research programs and technologies; the scope of protection we are able to establish and maintain for intellectual property rights covering our product candidates; anticipated developments related to our competitors and our industry; our competitive position and the success of competing therapies tha t are or may become available; our ability to maintain our current license agreements and collaborations and identify and enter into future license agreements and collaborations; the expected potential benefits of strategic collab orations with third parties and our ability to attract collaborators with development, regulatory, manufacturing or commercialization expertise; our reliance on third parties to conduct preclinical studies and clinical trials of our produ ct candidates; our ability to efficiently and cost -effectively conduct our current and future clinical trials; our reliance on third parties for the manufacture of our product candidates; our plans relating to sales strategy, manufacturing and commercializing our product candidates, if approved; anticipated regulatory developments in the United States and foreign countries in which we may seek regulatory approval for our product candidates in the future; the timing an d likelihood of the achievement of milestones pursuant to our existing collaboration agreements; our ability to attract and retain key scientific and management personnel; the costs of operating as a public company; the accuracy of ou r estimates regarding future expenses, future revenue, capital requirements and the need for additional financing; the period over which we estimate our existing cash and cash equivalents will be sufficient to fund our future ope rating expenses and capital expenditure requirements; our ability to obtain funding for our operations necessary to complete further development and commercialization of our current and future product candidates; our anticipated use of our existing resources, estimates of our expenses, capital requirements and needs for additional financing; general economic, political and market conditions, including inflationary pressures, interest rates, and changes in trade pol icy; and other factors specified in the Company's Registration Statement on Form 10, initially publicly filed by the Company with the Securities and Exchange Commission (the SEC ) on December 10, 2025 and in other filin gs and furnishings made by the Company with the SEC from time to time. Should one or more of these risks or uncertainties materialize, or should any of our assumptions prove incorrect, actual results may vary in material res pec ts from those projected in these forward -looking statements. We undertake no obligation to update or revise any forward -looking statements, whether as a result of new information, future events or otherwise, except as may be required under applicable securities laws. TRADEMARKS: This Presentation contains references to trademarks and service marks belonging to other entities. Solely for convenience, trademarks and trade names re ferred to in this Presentation may appear without the ® or TM symbols, but such references are not intended to indicate, in any way, that the applicable licensor will not assert, to the f ullest extent under applicable law, its rights to these trademarks and trade names. We do not intend our use or display of other companies’ trade names, trademarks or service marks to imply a relationship with, or endorsement or sponsors hip of us by, any other companies. PUBLIC DATA SOURCES: Certain facts, forecasts and other statistics in this Presentation have been derived from various public data sources. We believe that the sources of the information are appropriate sources for such information, and we have taken reasonable care in extracting and reproducing such information. However, such information has not been independently verified by us, our directors, officers, or representatives. Furthermore, any facts, forecasts, and other statistics from such sources may not be prepared on a comparable basis or may not be consistent w ith other sources. In addition, certain facts, forecasts and other statistics have been taken from public official sources or statements. Neither we nor any of our directors, officers or representatives are responsible for the accu racy, reliability or completeness of the information from such public data sources. For these reasons, you should not place undue reliance on such information. You should carefully consider the importance placed on such information or statistics. MARKET AND INDUSTRY DATA: This Presentation also contains information regarding our market and our industry that is derived f rom third-party research and publications. That information may rely upon a number of assumptions and limitations, and we have not independently verified its accuracy or completeness. This data is subject to change. No repr ese ntation is made as to the reasonableness of the assumptions made within or the accuracy or completeness of any projections or modeling or any other information contained herein. Any data based on past performance or modeling contained herein is not an indication as to future performance. 2
Our vision: To pioneer precision RNA medicines for the heart and profoundly improve the lives of people impacted by cardiac diseases Our vision: To pioneer precision RNA medicines for the heart and profoundly improve the lives of people impacted by cardiac diseases 3
Atrium has made solid progress since our launch in February 2026 KEY MILESTONES • ATR 1072 cleared for trials in the U.S. and Canada • First patient dosed in Phase 1/2 clinical trial – Corventis PRKAG2 syndrome patient identification: 1 Build bottom-up view of full patient population ATR 1072 & ATR 1086: 2 Expand into additional cardiomyopathies with shared pathways Next development candidate: 3 Build the pipeline in rare cardiomyopathy 4
Atrium is at the forefront of genetic cardiomyopathy treatment, and we're moving fast Patients and physicians are looking for more effective treatment options for genetic cardiomyopathies, and the market is primed for precision therapies Rare Cardiac Proven Ability Targeted Disease with High to Execute Platform, Unmet Need with Urgency Focused Pipeline Serious, genetically driven Atrium has dosed its first patient in A targeted RNA delivery platform cardiomyopathies with significant Corventis , the first interventional powering two lead programs - ATR unmet need - no approved disease - clinical trial for people living with 1072 (PRKAG2 syndrome) and ATR 1 modifying therapies exist today PRKAG2 syndrome (Ph 1/2) 1086 (PLN cardiomyopathy) – and two undisclosed precision cardiology targets 1 Hutt, E, et al, “Medical Treatment Strategies for Hypertrophic Cardiomyopathy.” American Journal of Cardiology vol 212, S33 -41 5
A precision RNA platform primed for genetic cardiomyopathies Monoclonal Oligonucleotide Antibody Oligonucleotide Antibodies Therapies Conjugate (AOC) OLIGO mAb mAb OLIGO Targeted Delivery Genetic Precision Scalable Platform ✓ RNA delivery technology designed ✓ Designed to directly target ✓ AOCs applicable across multiple to efficiently reach heart tissue pathogenic RNA genetically -defined cardiomyopathies ✓ Built on technology developed ✓ Potential to modify disease ✓ Efficient expansion potential to at Avidity including same antibody progression additional indications and linker 6
Leadership team expertise in rare disease and RNA Leadership team expertise in rare disease and RNA Rocio Martin | Chief Strategy Officer Kath Gallagher | Chief Executive Officer and Board Member 20+ years in various senior strategy, management and commercial roles in 20+ years in the biopharmaceutical industry leading portfolio strategy, clinical and commercial organizations program management, investor relations and corporate affairs in preclinical to commercial stage companies AVIDITY, KRONOS, AUDENTES, ULTRAGENYX, CELGENE AVIDITY, AKCEA, MERRIMACK Brendan Winslow | Chief Financial Officer Steve Hughes, MD | Chief Medical Officer 15+ years of financial leadership experience in biotech and diversified 25+ years in biopharmaceutical industry contributing to 50+ clinical trials and multiple product filings and healthcare, including global operations, commercialization and strategic launches in rare disease, cardiovascular and neurology therapy areas transformations AVIDITY, IONIS, BIOGEN, CSL BEHRING, SANOFI AVIDITY, ACADIA, BAXTER Stephanie Kenney | Chief Corporate Affairs Officer Husam Younis, PhD, PharmD | Chief Scientific Officer 25+ years in biopharmaceutical industry leading corporate affairs, investor 20+ years in drug discovery and development, including rare disease and relations and marketing at preclinical to commercial stage companies in SVP of development science at Avidity autoimmune, cardiovascular and renal therapy areas AVIDITY, NGM, IONIS, PFIZER AVIDITY, HANSA, ASTRAZENECA Atrium Board Members Troy Wilson Kath Gallagher Sarah Boyce (Chair) Simona Skerjenac Carsten Boess W. Michael Flanagan, Ph.D. 7
Robust wholly - owned pipeline supported by strong capital position CLINICAL ANTICIPATED UPCOMING TARGET RESEARCH IND- ENABLING PHASE 1 PHASE 2 PHASE 3 MILESTONES Initial POC data PRKAG2 syndrome PRKAG2 ATR 1072 expected 2H 2027 IND filing PLN PLN cardiomyopathy ATR 1086 in 2027 Development Undisclosed Rare cardiomyopathy candidate in 2027 Rare cardiomyopathy Undisclosed Research ongoing Strong $1.5B $264M balance sheet potential R&D milestone Cash, cash equivalents, and payments from existing runway through end of 2028, extending 1 investments as of June 30, 2026 2 collaborations with BMS and LLY beyond initial POC data in 2H 2027 1 Does not include the $15M milestone earned from Bristol Myers Squibb announced on August 13, 2026 or proceeds from the $50M private placement financing announced on October 8, 2026 8 2 Receipt of such milestone payments are subject to the terms and conditions of the collaboration agreements with BMS and LLY, respectively, assigned to the Company in connection with the Separation and Distribution from Avidity
About Genetic Cardiomyopathies 9
Millions of people with genetic cardiomyopathies lack disease - modifying treatments 1 Approximately 1% of patients with genetically driven cardiomyopathies are getting genetic testing ~2 Million 2 50% diagnosed in the US have underlying genetic Most managed through 3,4 5 driver of disease symptom control Limited targeted or etiology -specific 6 therapies today Opportunity for RNA - based precision therapies 1 Longoni, M. et al, “Real -world Utilization of Guideline -Directed Genetic Testing in Inherited Cardiovascular Diseases.” Front. C ardiovasc. Med 10:1272433 (2023) 2 Kramer ,C. Et al, Hypertrophic Cardiomyopathy Registry: The rationale and design of an international, observational study of hypert rophic cardiomyopathy. Am Heart J. 2015 Aug;170(2):223 -30 and Ababio, Yaa et al, Prevalence and Clinical Burden of Idiopathic Dilated Cardiomyopathy in the United States . Am J of Medicine Open Volume 10, 2023. 3 Ho, CY. “Genotype and lifetime burden of disease in hyptertrophic cardiomyopathy 4 Cheng , Z,. et al, “Hypertrophic Cardiomyopathy: From Phenotype and Pathogenesis to Treatment”. Frontiers in Cardiovascular Medicine vol. 8 (2021) . DOI=10.3389/fcvm.2021.722340 5 Hutt, E, et al, “Medical Treatment Strategies for Hypertrophic Cardiomyopathy.” American Journal of Cardiology vol 212, S33 -41 10 6 Aro, A. et al, Population Burden of Sudden Death Associated With Hypertrophic Cardiomyopathy”. Circulation vol 136 (2017)
Three phenotypes across the genetic cardiomyopathy spectrum Changes in cardiac structure and function can present independently and in combination Hypertrophic Dilated Arrhythmogenic Cardiomyopathy Cardiomyopathy Cardiomyopathy (ACM) (HCM) (DCM) Dyspnea, chest pain, Fatigue, exertional dyspnea, fluid retention, Palpitations, syncope, palpitations, syncope arrhythmias, thromboembolic events ventricular arrhythmias 11
ATR 1072 PRKAG2 Syndrome 12
PRKAG2 s yndrome A rare, progressive disease that can lead to sudden cardiac death • Autosomal dominant disease caused by gene mutations 0 in PRKAG2 that leads to AMPK overactivity resulting in Approved glycogen accumulation in heart muscle therapies • Contributes to cardiomyopathy due to thickened heart muscles, electrical conduction problems and arrhythmias 1,000 - 2,000 • Causes heart failure and sudden cardiac death People with PRKAG2 2 • Current treatment limited to symptom management for in the U.S. arrhythmias and myocardial hypertrophy • No therapy targeting root cause of disease ~100% • Typically emerges during adolescence and early of people inheriting a pathogenic 1 adulthood 3 mutation will develop symptoms 1 van der Steld , L et al. “PRKAG2 syndrome, a rare hypertrophic cardiomyopathy: a Brazilian long -term follow-up with extracardiac disorders.” Einstein (Sao Paulo, Brazil) vol. 22 eAO0549. 26 Jul. 2024, doi:10.31744/ einstein_journal/2024AO0549 2 Murphy, R, et al. “Adenosine Monophosphate -Activated Protein Kinase Disease Mimicks Hypertrophic Cardiomyopathy and Wolff -Parkinson -White Syndrome.” Journal of the American College of Cardiology vol 45 (2005). d oi:10.1016/j.jacc.2004.11.053 13 3 Hu, D, et al. “Identification, clinical manifestation and structural mechanisms of mutations in AMPK associated cardiac glyco gen storage disease.” EBioMedicine 54 (2020) 102723
PRKAG2 s yndrome prevalence likely exceeds our initial estimate This work continues, building towards a confident view of the full population Patient identification strategy is Early findings to uncover the focused in three areas already diagnosed Uncover the already - diagnosed Our initial prevalence estimate of 1,000 - 1 1 Direct, bottom -up engagement with major 2,000 PRKAG2 syndrome patients was genetic -testing labs conservative based on published literature Engage the patient community 2 Early efforts have already uncovered close to Build presence and advocacy where patients 2,000 individuals with the PRKAG2 mutation already are 2 so far from only a subset of engaged labs Move the field of genetic testing 3 True population likely larger - still unmeasured Partner across stakeholders to widen testing and recognition 1 Murphy, R, et al. “Adenosine Monophosphate -Activated Protein Kinase Disease Mimics Hypertrophic Cardiomyopathy and Wolff -Parkins on-White Syndrome.” Journal of the American College of Cardiology vol 45 (2005). doi:10.1016/j.jacc.2004.11.053 14 2 Data on file: Internal sources based on discussions with genetic testing providers
ATR 1072 designed to silence mutant PRKAG2 to normalize AMPK activity PRKAG2 is the regulatory Mutant PRKAG2 leads to Hypertrophic cardiomyopathy (HCM) characterized Mechanism component of AMPK overactivation of AMPK by glycogen accumulation and arrhythmia of Disease ATR 1072 - mediated degradation Reduced mutant PRKAG2 leads Attenuates HCM Therapeutic of cardiac PRKAG2 mRNA to normalization of AMPK activity disease progression Approach ATR 1072 15
Targeting PRKAG2 mRNA in the heart led to reversal of glycogen accumulation as well as improvement in other key 1 features of the disease in nonclinical model Cardiac glycogen accumulation reversed • Encouraging results in measures of 4 weeks after treatment hypertrophy include reduction in heart weight and left ventricular wall thickness 30 Glycogen • Treatment also led to improvement in p < 0.05 ✱ ECG parameters measuring electrical 20 conduction including PR interval • Further reinforces scientific rationale for 10 ATR 1072 targeting the root cause of PRKAG2 syndrome • Reversibility of downstream parameters 0 | | | consistent with earlier nonclinical data Untreated Disease After Treated Control Untreated features mATR 1072 diseased diseased established treatment mice mice 1 R302Q Data on file: Mice received PRKAG2 AAV for 3 wk followed by mATR 1072 (single dose 3 mg/kg, siRNA component), a mouse -active surrogate of ATR 1072 . 16 Data presented at 4 wk post mATR 1072; mean ± SD, n=9 -10/grp. *One-Way ANOVA Glycogen (μg/mg)
ATR 1072 improved measure of cardiac hypertrophy 1 in echocardiogram in nonclinical model Cardiac wall thickness decreased at 4 weeks after treatment Untreated diseased mice Treated diseased mice LVID LVID LVPW LVPW 1 mm LVID: Left ventricular internal diameter; LVPW: Left ventricular posterior wall thickness 1 Data on file. This is a representative echocardiogram image. 17
ATR 1072 has a favorable nonclinical safety profile and 1 robust target knockdown ATR 1072 activity in monkey heart following a ATR 1072 was generally well single dose at 28 days of treatment tolerated in 9 - month, repeat dose chronic toxicity study in PRKAG2 mRNA 150 cynomolgus monkey 125 • No dose limited toxicity in any organ 100 system at the highest dose tested 75 50 • No effects on cardiac function 25 associated with PRKAG2 mRNA 0 reduction including assessments of PBS ATR 1072 ECG, echocardiogram, histopathology (3 mg/kg) 18 1 Data on file: Based on preclinical studies PRKAG2 mRNA Relative to PBS (%)
ATR 1072: First trial targeting PRKAG2 syndrome ongoing Initial trial data demonstrating proof of concept anticipated in 2H 2027 48 - week treatment PART A - Dose Escalation* PART B - Expansion Long - Term Extension Cohort A1 Cohort A2 Cohort A3 Cohort B All participants 40 mg 80 mg 160 mg Recommended Ph 2 dose n = 4 n = 4 n = 4 n = 25 Safety review committee evaluation prior to dose escalation Open label adaptive trial design Primary endpoint: Incidence of treatment -emergent adverse events (TEAEs) ~37 participants enrolled, ~15 sites globally Secondary endpoints: PRKAG2 mRNA reduction and siRNA tissue concentrations Adults (18-65 yrs) w/ confirmed PRKAG2 mutation and (cardio biopsy in Part A only), plasma PK cardiac phenotype consistent with PRKAG2 syndrome Exploratory endpoints: Echocardiogram, ECG and Holter parameters, biomarkers, immunogenicity, clinical outcomes, and optional cardiac MRI findings 19 * Dose based on siRNA weight; flat dosing IV Q6W Equivalent to 0.5, 1.0, 2.0 mg/kg
ATR 1086 PLN Cardiomyopathy 20
PLN Cardiomyopathy A rare progressive disease with frequent family history • PLN -R14del is the most common disease - relevant PLN mutation 0 • Mutant PLN -R14del forms aggregates and impairs Approved cardiomyocyte function therapies • Characterized by dilated, arrhythmogenic or hypertrophic cardiomyopathy • Notable for frequent family history of premature sudden 2,000 - 4,000 cardiac death and progressive cardiac failure People with pathogenic PLN 2 • High incidence of sudden cardiac death, ventricular variants in the U.S. arrhythmias and cardiac transplantation 1 • Current treatment focuses on symptom management • No therapy to target root cause of disease 1 Vafiadaki E, et al. “ Phospholamban R14del disease: The past, the present and the future.” Frontiers in Cardiovascular Medicine vol 10 (2023). doi:10.3389/fcvm.2 02 3.1162205 21 2 Internal sources based on discussions with genetic testing providers
ATR 1086: Designed to silence mutant PLN to prevent 1 protein aggregates and target root cause of disease Phospholamban (PLN) regulates R14del mutation on PLN causes Dilated and Arrhythmogenic Mechanism Ca2+ handling in cardiomyocytes PLN to form protein aggregates cardiomyopathy (DCM & ACM) of Disease ATR 1086 mediated degradation Reduced mutant PLN prevents Attenuates DCM & ACM Therapeutic of cardiac PLN mRNA protein aggregate formation disease progression Approach ATR 1086 22 1 Data on file: Based on preclinical studies
ATR 1086 demonstrates functional improvement and 1 survival in preclinical model of disease Reduction of human PLN expression Improved survival (Kaplan - Meier survival curve) and ejection in the heart following treatment with fraction following repeated ATR 1086 treatment (6 mg/kg) in a ATR 1086 (6 mg/kg ) humanized mouse model of hPLNR14/R14 ATR 1086 ATR 1086 ATR 1086 PLN mRNA levels were measured in cardiac tissue in Ejection fraction measured at 6 -weeks of treatment. Dotted lines indicate WT levels. Data are presented as mean ± SEM. transgenic mice expressing hPLN WT. Student’s t -test, * p < 0.05. 23 1 Data on file: Based on preclinical studies
Expansion Opportunities for ATR 1072 and ATR 1086 A biology -driven pipeline with multiple indication expansion opportunities 24
ATR 1072 and ATR 1086 have opportunities for indication expansion beyond a single genetically defined population Central Pathways in Opportunities for Cardiac Function Indication Expansion AMPK dysregulation is implicated Energy sensing across multiple genetic PRKAG2 regulates AMPK AMPK ATR 1072 cardiomyopathies beyond activity, the key energy sensor in the heart PRKAG2 syndrome Influencing calcium cycling may Calcium handling improve diastolic function in PLN inhibits SERCA2a, an 2+ Ca ATR 1086 multiple cardiomyopathies beyond essential mediator of calcium cycling PLN cardiomyopathy 25
Atrium is accelerating momentum post - launch, with strong execution and multiple milestones ahead Achievements Anticipated Upcoming Milestones • GMP manufacturing• Initial proof-of-concept data by 2H 2027 • IND clearance and NOL ATR 1072 • First patient dosed in Corventis Ph 1/2 trial • Identified lead candidate• IND-enabling studies initiated in 2026 ATR 1086• Preclinical proof -of-concept • IND filing in 2027 • GMP manufacturing Rare • Identified two promising targets• Next development candidate in 2027 cardiomyopathies 26 26
Atrium has the expertise, leadership and focused pipeline to deliver in precision cardiology Execution Pipeline Platfor m Strong balance sheet with Focused pipeline with Proprietary RNA delivery experienced leadership indication expansion platform ideal for precision team opportunities cardiology 27 27
IR Contact Stephanie Kenney, Chief Corporate Affairs Officer investors@atrium -tx.com 28