Gene therapy with etranacogene dezaparvovec in haemophilia B: about the 1st patient infused in Spain

Introduction: Etranacogene dezaparvovec (ED) is the first gene therapy approved in Europe for severe or moderately severe haemophilia B without inhibitors. Its implementation in Spain began in 2024 as an alternative to conventional FIX prophylaxis. Objective: To describe the initial clinical experience and 3-month outcomes of the first patient treated with ED in Spain, in the context of the 5-year HOPE-B data. Materials and methods: Data collection from the patient’s electronic medical record. Results: A 41-year-old male with baseline FIX 1.6% and advanced arthropathy received a single intravenous dose of ED. Infusion was well tolerated, with immediate discontinuation of prophylaxis. FIX activity increased progressively to 49.9% at 3 months, placing the patient at the 67th percentile of the HOPE-B trial (mean 39.0 IU/dl at month 6; 36.1 ± 15.7 IU/dl at 5 years). Mild and transient transaminitis was managed with prednisone without additional complications. Conclusions: Initial results confirm the expected safety and efficacy of ED in real clinical practice, consistent with the long-term HOPE-B profile, and highlight the importance of careful patient selection and motivation.