At the time of designation, medicines containing factor IX were authorised in the EU for the treatment of haemophilia B, to replace the missing protein. However, factor IX medicines did not work in some patients with haemophilia B because the immune system (the body’s natural defences) can produce ‘inhibitors’ (antibodies) against factor IX which stop the factor IX medicine from working. In these cases, other treatments needed to be used, such as factor VIIa (the activated form of factor VII, another protein involved in blood clotting), either alone or as part of a combination treatment.

The sponsor has provided sufficient information to show that the medicine might be of significant benefit for patients with haemophilia B because preliminary data show that it can increase the amount of factor IX circulating in the blood. The way the medicine works means that patients may not need or may need less frequent treatment with factor IX medicines. This assumption will need to be confirmed at the time of marketing authorisation, in order to maintain the orphan status.