Capsida Biotherapeutics said it has closed its SYNRGY Phase I/II gene therapy trial for STXBP1 after a child death following infusion of CAP-002, with the company reporting cerebral edema as the cause of death. The trial had previously been placed on clinical hold after the event. In its latest public update, Capsida said it made the decision to close out the trial after additional laboratory research, though it stated it has not fully confirmed what drove the cerebral edema. The company also shared partial mechanism-of-action data, saying the AAV gene therapy engages ADAM15 to facilitate brain entry. Gene therapy safety scrutiny has intensified across the field, and Capsida’s closure adds further pressure on vector purity, immune activation risks and preclinical translation assumptions for CNS AAV approaches.