Company: SION
Filing Date: 2025-01-17
Form Type: S-1
Source: 0001193125-25-008474
Chunk: 315

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-17
Form: S-1
Chunk 315
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us relating to a contract or document
filed as an exhibit is qualified in all respects by the filed exhibit. The SEC also maintains an internet website that contains reports and other information about issuers, like us, that file electronically with the SEC. The address of that website
is www.sec.gov.

We currently do not file periodic reports with the SEC. On the completion of this offering, we will be subject to the
information reporting requirements of the Exchange Act, and we will file reports, proxy statements and other information with the SEC. These reports, proxy statements and other information will be available for review at the website of the SEC
referred to above.

We also maintain a website at www.sionnatx.com. Information contained in, or accessible through, our website is not a
part of this prospectus, and the inclusion of our website address in this prospectus is only as an inactive textual reference. Upon completion of this offering, you may access, free of charge, our annual reports on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K and amendment to those reported filed or furnished pursuant to
Section 13(a) or 15(d) of the Exchange Act as soon as reasonably practicable after such material is electronically filed with, or furnished to, the SEC.

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INDEX TO CONSOLIDATED FINANCIAL STATEMENTS Consolidated Financial Statements for the Years Ended December 31, 2023 and 2022:

| Report of Independent Registered Public Accounting Firm                  |     | F-2 |
| Consolidated Balance Sheets                                              |     | F-3 |
| Consolidated Statements of Operations and Comprehensive Loss             |     | F-4 |
| Consolidated Statements of Convertible Preferred Stock and Stockholders’ 
 Deficit                                                                  |     | F-5 |
| Consolidated Statements of Cash Flows                                    |     | F-6 |
| Notes to Consolidated Financial Statements                               |     | F-7 |

Unaudited Interim Condensed Consolidated Financial Statements for the Nine Months Ended September 30, 2024 and 2023:

| Condensed Consolidated Balance Sheets                                              |     | F-30 |
| Condensed Consolidated Statements of Operations and Comprehensive Loss             |     | F-31 |
| Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders’ 
 Deficit                                                                            |     | F-32 |
| Condensed Consolidated Statements of Cash Flows                                    |     | F-34 |
| Notes to