Exhibit 99.1 PRESS RELEASE Prothena Reports Third Quarter 2025 Financial Results and Business Highlights DUBLIN, Ireland, November 6, 2025 -- Prothena Corporation plc (NASDAQ:PRTA), a late-stage clinical biotechnology company with a robust pipeline of investigational therapeutics built on protein dysregulation expertise, today reported financial results for the third quarter and first nine months of 2025 and provided business highlights. "We are pleased with the advancement of our late-stage partnered clini ...