Company: SION
Filing Date: 2025-02-07
Form Type: 424B4
Source: 0001193125-25-022709
Chunk: 297

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-07
Form: 424B4
Chunk 297
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 not address all of the U.S. federal income or estate tax consequences that may be relevant to a non-U.S.holder in light of such non-U.S.holder’s particular circumstances. This discussion also does not consider any specific facts or circumstances that may be relevant to non-U.S.holders subject to special rules under the U.S. federal income or estate tax laws, including:

| • |     | U.S. expatriates, former citizens or long-term residents of the U.S.; |

| • |     | partnerships or other entities or arrangements treated as pass-through or disregarded entities for U.S. federal income tax 
 purposes (and investors therein);                                                                                          |

| • |     | “controlled foreign corporations”; |

| • |     | “passive foreign investment companies”; |

| • |     | corporations that accumulate earnings to avoid U.S. federal income tax; |

| • |     | banks, financial institutions, investment funds, insurance companies, brokers, dealers or traders in securities; |

| • |     | tax-exempt organizations and governmental organizations; |

| • |     | tax-qualified retirement plans; |

| • |     | persons who acquire our common stock through the exercise of an option or otherwise as compensation; |

| • |     | qualified foreign pension funds as defined in Section 897(l)(2) of the Code and entities all of the interests of which 
 are held by qualified foreign pension funds;                                                                           |

| • |     | persons that elect to apply Section 1400Z-2 of the Code to gains recognized 
 with respect to shares of our common stock;                                 |

| • |     | persons that own or have owned, actually or constructively, more than 5% of our common stock; |

| • |     | persons who have elected to mark securities to market; and |

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| • |     | persons holding our common stock as part of a hedging or conversion transaction or straddle, or synthetic security or a 
 constructive sale, or other risk reduction strategy or integrated investment.                                           |

If an entity or arrangement that is classified as a partnership for U.S. federal income tax purposes holds our common stock, the U.S. federal income tax treatment of a partner in the partnership will generally depend on the status of the partner, the activities of the partnership and certain determinations made at the partner level. Partnerships holding our common stock and the partners in such partnerships are urged to consult their tax advisors about the particular U.S. federal income tax consequences