INFORMATION STATEMENT Atrium Therapeutics, Inc. Distribution of Common Stock $0.001 par value This information statement is being furnished to existing stockholders of Avidity Biosciences, Inc. ("Avidity") in connection

INFORMATION STATEMENT

Atrium Therapeutics, Inc.

This information statement is being furnished to existing stockholders of Avidity Biosciences, Inc. ("Avidity") in connection with the pro rata

distribution (the "Distribution") by Avidity of all the issued and outstanding shares of common stock, par value $0.001 ("our common stock" or "Company Common Stock"), of Atrium Therapeutics, Inc.

("we," "us," "our," or the "Company") to holders of Avidity common stock, par value $0.0001 per share ("Avidity Common Stock"), as of the Record Date (as defined below). Prior to such

Distribution, Avidity will effect a pre-closing reorganization (the "Separation"), with such reorganization generally resulting in the Company owning, assuming or retaining all assets and

liabilities of Avidity and its subsidiaries exclusively related to its early stage precision cardiology programs, including ATR 1086 and ATR 1072, which (as described in more detail below) target rare genetic cardiomyopathies, including

phospholamban and Protein Kinase AMP-activated non-catalytic subunit Gamma 2 Syndrome, respectively, and certain collaboration agreements, including those

with Bristol-Myers Squibb Company and Eli Lilly and Company (the "Company Assets"), and Avidity owning, assuming or retaining all other assets and liabilities (the "RemainCo Business"). As described in this information

statement, the consummation of the Distribution (the "Spin-Off") is subject to the satisfaction or waiver by Avidity and the Company of certain conditions set forth in the Separation and

Distribution Agreement, dated as of October 25, 2025 (the "Separation Agreement"), among Avidity, the Company and Novartis AG, a company limited by shares (Aktiengesellschaft) incorporated under the laws of Switzerland

("Novartis") (with respect to certain sections therein), including (i) the satisfaction or waiver of certain conditions precedent included in the Agreement and Plan of Merger, dated as of October 25, 2025 (the "Merger

Agreement"), among Novartis, Ajax Acquisition Sub, Inc., a Delaware corporation and an indirect wholly owned subsidiary of Novartis ("Merger Sub"), and Avidity, pursuant to which, on the terms and conditions set forth in the Merger

Agreement, Merger Sub will merge with and into Avidity (the "Merger"), with Avidity surviving the Merger as an indirect wholly owned subsidiary of Novartis, (ii) the absence of any judgment, ruling, order, writ, injunction, award,

decision, assessment or decree of any governmental authority preventing the consummation of the Separation, the Distribution or the Merger and any law enacted or deemed applicable to any such transaction by any governmental authority of competent

jurisdiction that makes consummation of the Separation, the Distribution or the Merger illegal, and (iii) the execution of documentation effecting transfer of the Third Party Agreements (as defined below) from Avidity to the Company, in form

reasonably satisfactory to Novartis, among others.

Pursuant to the terms of the Merger Agreement and the Separation Agreement, Avidity may also consummate

a sale of all of the Company to a third party (a "Permitted Third Party Sale"), after which, the Distribution would not be effected and cash proceeds received by Avidity, any of its affiliates or the Company from such sale, net of

expenses incurred in connection with or related to the authorization, preparation, negotiation, execution and performance of such transaction and any definitive agreements related thereto would be distributed to Avidity's stockholders and

holders of options to purchase shares of Avidity Common Stock (the "Avidity Stock Options") and holders of restricted stock units denominated in shares of Avidity Common Stock, whether subject to time-based or performance-based vesting,

that are granted under any equity plans, agreements or arrangements of Avidity ("Avidity RSUs" and together with the Avidity Stock Options, the "Avidity Equity Awards"). In addition, the transfer of assets to the Company

includes certain Avidity assets (the "ROFN Assets") that triggered a right of first negotiation ("ROFN") with an existing collaboration partner of Avidity (the "ROFN Holder"). Avidity was permitted to negotiate

the sale of Avidity assets subject to the ROFN ("ROFN Sale") with the ROFN Holder, and, if an agreement was reached, consummate the sale of all or a portion of such assets. On February 5, 2026, the negotiation period under the ROFN

expired and, as a result, no ROFN Sale will occur.

Holders of Avidity Common Stock as of the close of business, Eastern Time, on February 12, 2026 (the

Company Common Stock pursuant to the Distribution. Each such holder will receive one share of Company Common Stock for every

ten shares of Avidity Common Stock held on the Record Date (the "Distribution Ratio"). If you sell shares of Avidity Common Stock up to and including the close of business on the

Distribution Date, you will be selling your right to receive Company Common Stock with respect to those shares in the Distribution to the purchaser of such shares. There will not be any trading of Company Common Stock on a "when-issued"

basis or any "ex-distribution" trading of Avidity Common Stock before 9:30 a.m., Eastern Time, on the trading day following the Distribution Date (the "Ex-Dividend Date"). This means that Company Common Stock will not trade

separately from Avidity Common Stock prior to the Ex-Dividend Date. For Avidity stockholders who own shares of Avidity Common Stock in registered form on the Record Date through the Distribution Date, the

transfer agent will credit their shares of Company Common Stock to book entry accounts established in their names to hold their shares of Avidity Common Stock. Our distribution agent will send these stockholders a statement reflecting their

ownership of shares of Company Common Stock shortly after the Distribution Date. For stockholders who own shares of Avidity Common Stock through a broker or other nominee, the shares of Company Common Stock received in the Distribution will be

credited to their accounts by the broker or other nominee on or after the Ex-Dividend Date. Avidity stockholders will receive cash in lieu of fractional shares of the Company. The Distribution will be taxable

to holders of Avidity Common Stock. See "The Separation and Distribution-Material U.S. Federal Income Tax Consequences and "-No When-Issued Trading or Ex-Distribution Trading" for further information.

Although stockholder approval of the Distribution is not required, such approval is being sought in connection with transactions described in Avidity's

Definitive Proxy Statement on Schedule 14A, which was filed with the Securities and Exchange Commission ("SEC") on January 30, 2026 (File No. 001-39321) (as amended or supplemented, the

"Proxy Statement"). We are not asking you for any other proxy, and you are requested not to send us any proxy. Avidity stockholders will not be required to pay for Company Common Stock to be received by them in the Distribution, or to

surrender or to exchange Avidity Common Stock in order to receive Company Common Stock, or to take any other action in connection with the Distribution. There is currently no trading market for Company Common Stock. We have been approved to list

Company Common Stock on The Nasdaq Global Select Market ("Nasdaq") under the symbol "RNA," which is currently the symbol for the shares of Avidity Common Stock listed on Nasdaq. To facilitate the Distribution and transition

of the stock symbol in connection with the closing of the Merger, Avidity Common Stock will temporarily trade on the Nasdaq Global Market under "RNAM." See "The Separation and Distribution-No When-Issued Trading or

Ex-Distribution Trading" for further information.

IN REVIEWING THIS INFORMATION STATEMENT, YOU SHOULD CAREFULLY CONSIDER THE MATTERS DESCRIBED

UNDER THE CAPTION "RISK FACTORS" BEGINNING ON PAGE 18.

WE ARE AN EMERGING GROWTH COMPANY AS DEFINED IN THE

JUMPSTART OUR BUSINESS STARTUPS ACT OF 2012 AND A SMALLER REPORTING COMPANY AND WE CANNOT BE CERTAIN IF THE REDUCED REPORTING REQUIREMENTS APPLICABLE TO EMERGING GROWTH COMPANIES AND SMALLER REPORTING COMPANIES WILL MAKE OUR COMMON STOCK LESS

ATTRACTIVE TO INVESTORS. REFER TO "RISK FACTORS-RISKS RELATED TO OUR COMMON STOCK."

NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR

ANY STATE SECURITIES COMMISSION HAS APPROVED OR DISAPPROVED THESE SECURITIES OR DETERMINED IF THIS INFORMATION STATEMENT IS TRUTHFUL OR COMPLETE. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

THIS INFORMATION STATEMENT DOES NOT CONSTITUTE AN OFFER TO SELL OR THE SOLICITATION OF AN OFFER TO BUY ANY SECURITIES.

Avidity stockholders with inquiries related to the Distribution should contact our distribution agent, Computershare Trust Company N.A., at (800) 564 6253.

The date of this information statement is February 26, 2026.

PRESENTATION OF INFORMATION

The Company Business (as defined below) has not historically operated as a standalone business, and the financial information of the Company Business

contained in this information statement is derived from the consolidated financial statements and accounting records of Avidity. All historical financial information included within this information statement is that of the Company Business and not

of the Company as the Company has had no operations or activity as described below.

In connection with the Separation and the Distribution, Avidity

expects to assign to the Company, the agreements, leases, licenses and other contracts and assets necessary for the Company to conduct the business described in this information statement.

The Company was incorporated on September 30, 2025 as a wholly owned subsidiary of Avidity and has had no significant operations or activity other than

its initial issuance of shares of Company Common Stock for a nominal consideration and entry into the Separation Agreement and the RemainCo License Agreement (as defined below). Prior to the Distribution, and pursuant to the Separation, Avidity will

undergo an internal reorganization that will generally (as described in more detail below) result in (a) the Company owning, assuming or retaining all assets and liabilities of Avidity and its subsidiaries exclusively related to Avidity's

early stage precision cardiology programs, and certain collaboration agreements, including those with Bristol-Myers Squibb Company and Eli Lilly and Company (the "Third Party Agreements"), and

(b) RemainCo (as defined below) owning, assuming or retaining all other assets and liabilities of Avidity and its subsidiaries.

QUESTIONS AND ANSWERS ABOUT THE SEPARATION AND DISTRIBUTION

The following is a brief summary of the terms of the Separation and Distribution. Please see "The Separation and Distribution" for

a more detailed description of the matters described below.

Q: What are the Separation and Distribution?

A: The Separation is the method by which Avidity will separate the Company Business from Avidity's other business, creating two separate companies. The

Separation will generally result in (i) the Company owning, assuming or retaining all assets and liabilities of Avidity and its subsidiaries exclusively related to Avidity's early stage precision cardiology programs, including ATR 1086

and ATR 1072, which target rare genetic cardiomyopathies, including phospholamban and Protein Kinase AMP-activated non-catalytic subunit Gamma 2 Syndrome, respectively,

and the Third Party Agreements, and (ii) Avidity owning, assuming or retaining all other assets and liabilities of Avidity and its subsidiaries (Avidity following the Separation and Distribution, "RemainCo").

In the Distribution, Avidity will distribute to its stockholders as of the Record Date who hold their shares of Avidity Common Stock through the Distribution

Date, on a pro rata basis, all of our common stock. Following the Separation and Distribution, we will be a separate company from RemainCo, and RemainCo will not retain any ownership interest in us. The number of shares of Avidity Common Stock you

own will not change as a result of the Distribution.

Q: What is being distributed in the Distribution?

A: 15,514,966 shares of our common stock will be distributed in the Distribution, based upon 155,149,646 shares of Avidity Common Stock outstanding

on February 12, 2026. Company Common Stock to be distributed by Avidity in the Distribution and the shares of Company Common Stock issuable upon vesting of the Make Whole Awards (as defined below) to holders of Avidity Equity Awards pursuant to the

Merger Agreement and Separation Agreement will constitute all of our issued and outstanding common stock immediately after the Separation and Distribution. Fractional shares will be aggregated into whole shares of Company Common Stock and sold in

the public market by the distribution agent and stockholders will receive a cash payment in lieu of a fractional share. For more information on the shares being distributed in the Distribution, see "Description of Securities."

Q: What will I receive in the Distribution?

Holders of Avidity Common Stock will receive a distribution of Company Common Stock equal to one share of Company Common Stock for every ten shares of Avidity Common Stock held by them on the Record Date and through the Distribution Date. As a

result of the Distribution, you will own, as of the effective time of the Distribution, the same percentage of equity securities and voting power in the Company as you own in Avidity. For a more detailed description, see "The Separation and

Q: What is the record date for the Distribution?

A: Ownership of Avidity Common Stock was determined as of the close of business, Eastern Time, on February 12, 2026, which we refer to as the

receive shares of Company Common Stock pursuant to the Distribution. Each such holder will receive one share of Company Common Stock for every ten shares of Avidity Common Stock held on the Record Date. If you sell Avidity Common Stock up to and

including the close of business on the Distribution Date, you will be selling your right to receive Company Common Stock in the Distribution. See "The Separation and Distribution-No When-Issued Trading or Ex-Distribution

Trading" for further information.

Q: When will the Distribution occur?

A: Subject to the satisfaction or waiver of the conditions to the Spin-Off described below, it is expected that the Distribution will occur on

February 26, 2026. We expect trading of shares of Company Common Stock to begin on the trading day following the Distribution Date.

the relationship between RemainCo and us be following the Distribution?

A: Following the Distribution, we will be a public company and RemainCo will

have no continuing ownership interest in us. We and Avidity entered into the Separation Agreement for the purpose of accomplishing, among other things, the Separation of the Company Business and the Distribution of shares of Company Common Stock to

stockholders of Avidity. On October 25, 2025, we entered into the License Agreement with Avidity (the "RemainCo License Agreement"), pursuant to which we granted to Avidity certain exclusive and

non-exclusive licenses under our platform technology and other intellectual property, and Avidity granted to us certain exclusive and non-exclusive licenses under

certain RemainCo intellectual property, in each case taking effect upon the effective date of the earlier to occur of any Permitted Third Party Sale and the Distribution. Concurrently with the Distribution, we will enter into a transition services

agreement with RemainCo (the "Transition Services Agreement"), pursuant to which we will provide certain transition services to RemainCo, and RemainCo will provide certain transition services to us. Under the Separation Agreement,

Avidity and the Company agreed to indemnify, defend and hold harmless the other party, and its affiliates and certain representatives, from and after the Distribution Date, from losses in connection with, among other things, (i) the liabilities

assigned to, or retained by, the other party, as applicable, and the failure to pay, perform or otherwise discharge such liabilities, (ii) the breach by such party of the Separation Agreement, and (iii) any untrue statement or alleged