IN APRIL HILARY CASS, a British paediatrician, published her review of gender-identity services for children and young people, commissioned by NHS England. It cast doubt on the evidence base for youth gender medicine. This prompted the World Professional Association for Transgender Health (WPATH), the leading professional organisation for the doctors and practitioners who provide services to trans people, to release a blistering rejoinder. WPATH said that its own guidelines were sturdier, in part because they were “based on far more systematic reviews”.