Company: SION
Filing Date: 2025-02-07
Form Type: 424B4
Source: 0001193125-25-022709
Chunk: 280

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-07
Form: 424B4
Chunk 280
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 has sole or shared voting power or investment power. Unless otherwise indicated below, to our knowledge the persons and entities named in the table have sole voting and sole investment power with respect to all shares that they beneficially owned, subject to community property laws where applicable. We have deemed shares of common stock subject to options that are currently exercisable or exercisable within 60 days of December 31, 2024, to be outstanding and to be beneficially owned by the person holding the option for the purpose of computing the percentage ownership of that person but have not treated them as outstanding for the purpose of computing the percentage ownership of any other person. Applicable percentage ownership before the offering is based on an aggregate of 31,947,927 shares of common stock (which includes 75,958 shares of restricted common stock) deemed to be outstanding as of December 31, 2024, after giving effect to the automatic conversion of all outstanding shares of preferred stock into 27,149,206 shares of common stock immediately prior to the completion of this offering, and based on the initial public offering price of $18.00 per share. Applicable percentage ownership after the offering is based on 42,536,160 shares of common stock assumed to be outstanding immediately after the completion of this offering (including the sale of shares of common stock in this offering and assuming no exercise of the underwriters’ option to purchase additional shares), and does not include any shares which may be purchased by any person or entity named in the table in this offering. Unless otherwise indicated, the address for each beneficial owner listed in the table below is c/o Sionna Therapeutics, Inc., 21 Hickory Drive, Suite 500, Waltham, MA 02451.

|                                                                             |     | Before Offering |           |     |               |       |     | After Offering |           |     |               |       |
| Name of Beneficial Owner                                                    |     | Number of       
 Shares          
 Beneficially    
 Owned           |           |     | Percentage of 
 Shares        
 Beneficially  
 Owned         |       |     | Number of      
 Shares         
 Beneficially   
 Owned          |           |     | Percentage of 
 Shares        
 Beneficially  
 Owned         |       |
| 5% or Greater Shareholders:                                                 |     |                 |           |     |               |       |     |                |           |     |               |       |
| Entities affiliated with Atlas Venture(1)                                   |     |                 | 3,634,020