Long-Term Effects of Hemophilia B Gene Therapy Reply

To the Editor: The results reported by Mahlangu et al. in the GENEr8-1 trial1 and by Pipe et al. in the HOPE-B trial2 (Feb. 23 issue) represent a historic moment in the treatment of hemophilia. When there is enormous variability in response, as in these trials, the value of mean and median levels of factors VIII and IX is limited to comparisons between studies and in following cohorts of patients over time. Patients with hemophilia who are considering gene therapy are usually more interested in the potential response in themselves as individuals rather than in the overall mean and median. © 2023 Massachusetts Medical Society.