Company: SION
Filing Date: 2025-01-17
Form Type: S-1
Source: 0001193125-25-008474
Chunk: 123

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-17
Form: S-1
Chunk 123
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                                                                                                                                                     |     |                          | (165,238 | ) |     |           | (165,238 | ) |     |                |   |
| Total stockholders’ (deficit) equity                                                                                                                                    |     |                          | (148,549 | ) |     |           |  181,819 |   |     |                |   |
| Total capitalization                                                                                                                                                    |     | $                        |  181,819 |   |     | $         |  181,819 |   |     | $              |   |

| (1) | Each $1.00 increase or decrease, as applicable, in the assumed initial public offering price of $  per share, 
 the midpoint of the estimated offering price range listed on the cover page of this                           |

88

| prospectus for this offering, would increase or decrease, as applicable, the pro forma as adjusted amount of each of cash, cash equivalents and investments in marketable securities, additional paid-in capital, total stockholders’ equity and total capitalization by $  million, assuming that the number of shares offered by us in this offering remains the same and after deducting estimated 
 underwriting discounts and commissions, placement agent fees and estimated offering expenses payable by us. Similarly, each increase or decrease, as applicable, of 1.0 million shares in the number of shares of common stock offered by us at the                                                                                                                                                   
 assumed initial public offering price per share, the midpoint of the estimated offering price range listed on the cover page of this prospectus in this offering, would increase or decrease, as applicable, the pro forma as adjusted amount of each of                                                                                                                                              
 cash, cash equivalents and investments in marketable securities, additional paid-in capital, total stockholders’ equity and total capitalization by $  million, after deducting estimated                                                                                                                                                                                                             
 underwriting discounts and commissions and estimated offering expenses payable by us.                                                                                                                                                                                                                                                                                                                 |

The number of shares of common stock that will be outstanding after this offering on a pro forma and pro forma as adjusted basis is based on 46,656,571 shares of common stock (which includes 174,807 shares of restricted common stock) outstanding as of September 30, 2024 after giving effect to the automatic conversion of all outstanding shares of our preferred stock into the aggregate of 39,667,715 shares of common stock immediately prior to the completion of this offering, and excludes:

| • |     | 5,336,077 shares of