Capsida BioTherapeutics announced a voluntary hold on its SYNRGY Phase I/IIa clinical trial following the death of the first treated pediatric patient with STXBP1-related disorders, a rare neurodevelopmental disease characterized by severe epilepsy and cognitive impairment. The gene therapy candidate CAP-002, based on AAV vector delivery, is being evaluated for safety and efficacy in 12 patients. The company has alerted the FDA and is collaborating with experts to determine the cause while the trial remains on indefinite hold. The incident underscores safety challenges in rare gene therapy development.