A Long-Term Follow-Up Study of Haemophilia B Patients Who Have Undergone Gene Therapy

Severe haemophilia B (HB) is a bleeding disorder where a protein made by the body to help make blood clot is either partly or completely missing. This protein is called a clotting factor; with severe HB, levels of clotting Factor IX (nine; FIX) are very low and affected individuals can suffer life threatening bleeding episodes. HB mainly affects boys and men (approximately one in every 30,000 males). Current treatment for HB involves intravenous infusions of FIX as regular treatment (prophylaxis) or 'on demand' treatment. On demand treatment is highly effective at stopping bleeding but cannot fully reverse long-term damage that follows after a bleed. Regular treatment can prevent bleeding; however it is invasive for patients and also expensive. This clinical study aims to investigate the long-term safety and durability of FIX activity in participants who have been dosed with a new gene therapy product (FLT180a) in earlier clinical studies. Following administration, FLT180a results in production of FIX in the participants' liver cells which is then released into the blood stream. The aim is to have the participants' own body produce levels of FIX that allow for clotting to occur as normal as would be seen in a non-HB individual. This would remove the need for prophylaxis or on demand treatment following just a single administration of FLT180a. Up to 50 participants who have already been administered with FLT180a in the EU and US will take part in this study. Participants will be followed up in this trial until they have reached 15 years after being dosed. Participants will undergo procedures including physical examinations, join assessments, blood tests and liver ultrasounds. Participants will also need to complete a diary to document occurrence of bleeding episodes and record the amount of Factor IX concentrate they receive. Patient reports outcomes including measures of Quality of Life, disability and physical activity will also be collected.