Capsida Biotherapeutics confirmed it closed its SYNRGY Phase I/II gene therapy trial for STXBP1-related DEE after the previously reported death of a child who received CAP-002. The company cited the need to better understand what happened, while noting that trial safety remains unknown. Capsida also disclosed a partial mechanism of action, saying the AAV gene therapy engages with the protein ADAM15 to support entry into the brain. However, the company did not resolve the underlying driver of fatal cerebral edema, leaving the field to watch for later mechanistic findings and vector-related learnings from the broader AAV gene therapy landscape.