Within paediatric ependymoma cohorts, four molecular subtypes represent the vast majority of cases including the infratentorial Group A PF-EPN-A and Group B (PF-EPN-B), as well as supratentorial RELA-fusion positive (ST-EPN-RELA) and YAP1-fusion positive (ST-EPN-YAP1) ependymomas with Group A and ST-EPN-RELA being the most aggressive subtypes. The gene discussed is YAP1; the disease is ependymoma.