Capsida Bio has suspended its SYNRGY trial of CAP-002, an AAV-based gene therapy for rare STXBP1 encephalopathy, following the death of the first treated child patient. The affected disease causes severe neurodevelopmental impairment. The company is working urgently to determine the cause and has informed the FDA. The halt raises concerns about safety risks in gene therapy trials for rare neurological disorders and highlights the complexities of AAV delivery in pediatric populations.