Haemophilia A is a rare genetic disorder estimated to occur in one out of 10,000 live births, characterized by a deficiency in coagulation factor VIII causing impaired haemostasis and prolonged bleeding episodes. Moderate haemophilia, defined as < 5%, and severe haemophilia, defined as < 1% of normal factor VIII activity result in frequent and spontaneous bleeds into muscles and joints, commonly the elbows, knees, and ankles. Bleeding into joints can cause acute pain and swelling and can result in reduced joint range of motion, long-term cartilage damage and debilitating haemophilic arthropathy. Early use of prophylaxis with factor VIII replacement is recommended following diagnosis of haemophilia A to maintain joint health and prevent joint destruction. However, despite the use of prophylaxis many patients still experience joint bleeds which may lead to joint deterioration over time. The risk of joint bleeds increases with the amount of time spent below certain FVIII trough levels, e.g. 1, 3 or 5 IU/dL. Thus, there is probably a relation between the intensity of the prophylactic treatment regimen and joint health. Elocta is an extended half-life rFVIII product (EHL rFVIII), with a slower clearance as compared to conventional FVIII products. Treatment with Elocta will therefore provide the treater with a greater flexibility for individualizing prophylaxis as compared to conventional FVIII. Higher trough levels can be reached with Elocta without increasing factor usage or injection frequency. The treater can instead choose to reduce the injection frequency or the factor consumption without lowering trough levels.

The purpose of this study is to evaluate the effectiveness of Elocta on joint health over a long observation period (48 months). The study will explore the influence on long term joint health of different Elocta prophylaxis regimens leading to different trough levels.