A Study to Investigate the Course of Synovial Hypertrophy in Patients With Haemophilia A on Efanesoctocog Alfa Prophylaxis

This is a 12-month, multicentre, open-label, non-randomized, interventional single-arm study to assess the course of synovial hypertrophy in previously treated patients ≥12 years of age with moderate or severe haemophilia A achieving high sustained FVIII levels provided by weekly efanesoctocog alfa prophylaxis. To be eligible to enroll in the study, patients must have existing synovial hypertrophy in at least one of the 6 index joints (ankles, elbows, and knees) as assessed by the HEAD-US scoring system. A retrospective data collection on patients' haemophilia, medical, and surgical history will be performed, including a 12-month history of previous treatment and treated bleeding episodes. The study will start with the Screening Visit, which can be conducted up to 45 days prior to the Baseline Visit (Day 1), to check whether the patient fulfils all the inclusion criteria and none of the exclusion criteria. Patients will have an ultrasound examination of all non-prosthetic index joints at screening. The ultrasound images will be sent for central reading assessment using the HEAD-US scoring system to determine whether the patient has at least one eligible joint required for study inclusion. Once it is confirmed that a patient is eligible for inclusion, he/she will be enrolled in the study and attend a mix of on-site visits and phone call visits. The results from central reading assessment will be sent to the study sites and included in the baseline characteristics of the patients. MRI examinations can be conducted at the Baseline Visit or up to 28 days afterwards. Images from MRI will also be sent for central reading assessment using the International Prophylaxis Study Group (IPSG) MRI scale. The central reading assessment will be sent to the study sites and included in the patient data. Patients will be treated with once-weekly efanesoctocog alfa (50 IU/kg) prophylaxis and will complete the patient diary with their dosing and bleeding information. Assessments will be conducted during the on-site visits, which will occur every 6 months, and during phone call visits, which will occur halfway between these visits. A Safety Follow-up Call will be conducted 14 (+7) days after the End of Treatment (EoT) Visit. Ultrasound and MRI will be used to detect changes in synovial hypertrophy in index joints of patients. The primary endpoint of improvement in existing synovial hypertrophy from baseline to Month 12 as well as the key secondary endpoint of detection of new synovial hypertrophy and change in joint health status from baseline to Month 6 or Month 12 will be assessed using ultrasound and the HEAD-US scoring system. To obtain 100 eligible index joints, the target is to enroll approximately 35 patients.