Company: SION
Filing Date: 2025-02-03
Form Type: S-1/A
Source: 0001193125-25-018825
Chunk: 323

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-03
Form: S-1/A
Chunk 323
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 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.

229

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 Condensed Consolidated Financial Statements                               |     | F-35 |

F-1

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To the stockholders and the Board of Directors of Sionna Therapeutics, Inc.

Opinion on the Financial Statements

We have audited the accompanying
consolidated balance sheets of Sionna Therapeutics, Inc., and subsidiary (the “Company”) as of December 31, 2023 and 2022, the related consolidated statements of operations and comprehensive loss, convertible preferred stock and
stockholders’ deficit, and cash flows, for the years then ended, and the related notes (collectively referred to as the “financial statements”). In our opinion, the financial statements present fairly, in all material respects, the
financial position of the Company as of December 31, 2023 and 2022, and the results of its operations and its cash flows for the years then ended in conformity with accounting principles generally accepted in the United States of America.

Basis for Opinion