EXHIBIT 99.1

JOINT FILING AGREEMENT

This Joint Filing Agreement, dated as of April 2, 2026, is by and among RA Capital Management, L.P., Peter Kolchinsky, Rajeev Shah and RA Capital Healthcare Fund, L.P. (the foregoing are collectively referred to herein as the “Filers”).

Each of the Filers may be required to file with the United States Securities and Exchange Commission a statement on Schedule 13G and/or 13D with respect to common stock, par value $0.0001 per share of Karyopharm Therapeutics Inc. beneficially owned by them from time to time.

Pursuant to and in accordance with Rule 13(d)(1)(k) promulgated under the Securities Exchange Act of 1934, as amended, the Filers hereby agree to file a single statement on Schedule 13G and/or 13D (and any amendments thereto) on behalf of each of such parties, and hereby further agree to file this Joint Filing Agreement as an exhibit to such statement, as required by such rule.

This Joint Filing Agreement may be terminated by any of the Filers upon one week’s prior written notice or such lesser period of notice as the Filers may mutually agree.

Executed and delivered as of the date first above written.

RA CAPITAL MANAGEMENT, L.P.

By:

/s/ Peter Kolchinsky

Name:

Peter Kolchinsky

Title:

Authorized Signatory

PETER KOLCHINSKY

/s/ Peter Kolchinsky

RAJEEV SHAH

/s/ Rajeev Shah

RA CAPITAL HEALTHCARE FUND, L.P.

By:

RA Capital Healthcare Fund GP, LLC

Its:

General Partner

By:

/s/ Peter Kolchinsky

Name:

Peter Kolchinsky

Title:

Manager

Karyopharm Therapeutics Inc. SCHEDULE 13G