Exhibit 99.1 PRESS RELEASE Prothena Reports Second Quarter 2025 Financial Results and Business Highlights DUBLIN, Ireland, August 4, 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 second quarter and first six months of 2025 and provided business highlights. "We are excited that our partner Roche is advancing prasinezumab into P ...