SectionsMy IBDMy ProductsRecently SearchedTechnologyLicensingALLISON GATLINUpdated 04:52 PM ET 09/03/2026Ultragenyx stock crashed Thursday, losing almost half its value, after its experimental Angelman treatment failed in final-phase testing. Angelman syndrome causes developmental delays, balance problems and speech impairment. In the Phase 3 test, patients treats with Ultragenyx Pharmaceuticals' (RARE) drug, apazunersen, didn't show improvements in cognition. They also missed on a second metric, a composite score examining whether patients responded…Copyright ©2026 Investor's Business Daily, LLC. All rights reserved. 87990cbe856818d5eddac44c7b1cdeb8INVESTING RESOURCESTake a Trial TodayGet instant access to exclusive stock lists, expert market analysis and powerful tools with 2 months of IBD Digital for only $20!IBD VideosGet market updates, educational videos, webinars, and stock analysis.Get StartedLearn how you can make more money with IBD's investing tools, top-performing stock lists, and educational content.