Company: SION
Filing Date: 2025-02-07
Form Type: 424B4
Source: 0001193125-25-022709
Chunk: 240

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-07
Form: 424B4
Chunk 240
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| • |     | reviewing and establishing general policies relating to compensation and benefits of our employees, including our overall 
 compensation philosophy.                                                                                                  |

Our compensation committee will operate under a written charter, which will be effective upon the completion of this offering, that satisfies the applicable Nasdaq Listing Rules. 176

Nominating and Corporate Governance Committee Our nominating and corporate governance committee currently consists of Paul Clancy, M.B.A., chair of our nominating and corporate governance committee, Marcella Kuhlman Ruddy, M.D. and Peter A. Thompson, M.D. Our board of directors has determined that each member of the nominating and corporate governance committee is independent under the Nasdaq Listing Rules, a non-employeedirector, and free from any relationship that would interfere with the exercise of his or her independent judgment. The primary purpose of the nominating and corporate governance committee is to discharge the responsibilities of our board of directors with respect to our corporate governance functions and to identify, communicate with, evaluate and recommend candidates for our board of directors. Specific responsibilities of our nominating and corporate governance committee include:

| • |     | identifying and evaluating candidates, including the nomination of incumbent directors for reelection and nominees 
 recommended by stockholders, to serve on our board of directors;                                                   |

| • |     | considering and making recommendations to our board of directors regarding the composition and chairmanship of the 
 committees of our board of directors;                                                                              |

| • |     | instituting plans or programs for the continuing education of our board of directors and orientation of new directors; |

| • |     | developing and making recommendations to our board of directors regarding corporate governance guidelines and matters; and |

| • |     | overseeing periodic evaluations of the board of directors’ performance, including committees of the board of directors 
 and management.                                                                                                        |

Our nominating and corporate governance committee will operate under a written charter, which will be effective upon the completion of this offering, that satisfies the applicable Nasdaq Listing Rules. Code of Business Conduct and Ethics In connection with this offering, we adopted an amended and restated code of business conduct and ethics that applies to all our employees, officers and directors, to be effective upon the effectiveness of the registration statement of which this prospectus forms a part. This includes our principal executive officer, principal financial officer and principal accounting officer or controller, or persons performing similar functions. The full text of our code of business conduct and ethics will be posted on our website at www.sionnatx.com