The primary aim of this study is to prospectively investigate the current bleeding tendency of children and adults with VWD.

Von Willebrand disease (VWD) is the most common inherited bleeding disorder, and is characterized by a defective platelet adhesion and aggregation. VWD is caused by a reduced (type 1), an abnormal function (type 2) or a complete absence (type 3) of von Willebrand factor (VWF).

In recent years, large retrospective cohort studies have provided valuable insights on the clinical presentation, bleeding phenotype, quality of life, diagnostics, genetics and treatment of patients with VWD. One of these large studies is the von Willebrand in the Netherlands (WiN) study, which is a nationwide cross sectional study of moderate and severe von Willebrand disease patients, that was initiated in 2007. Over 800 VWD patients were included in the WiN study, which was about 80% of all known VWD patients in the Netherlands. Although the WiN study and large retrospective studies in other countries provided important insights in understanding VWD, some significant challenges remain and large prospective studies are lacking to provide answers.

All large retrospective cohort studies have assessed the bleeding phenotype of patients with VWD using bleeding scores or retrospective questionnaires. Bleeding scores calculate the sum of all bleeding episodes during lifetime. Therefore, they provide useful information on the bleeding tendency during lifetime. However, bleeding scores do not provide information on the change of bleeding tendency. If a patient had a period in his or her lifetime in which he or she had many bleeding episodes, then the bleeding score is high. Though, the patient could have had those bleeds 30 years ago and did not have a bleeding episode since then. Therefore, bleeding scores do not provide information on the current bleeding phenotype of VWD patients. Furthermore, previous studies provided limited information on the frequency of mild bleedings, like gum bleeding or epistaxis, that occur in daily life but do not require therapy. Nevertheless, these bleeding episodes can cause a major impairment in quality of life. This is especially important in children, because school-going children with VWD have a lower quality of life and have a different bleeding tendency, characterized by more cutaneous bleeding (81%), oropharyngeal bleeding (64%) and epistaxis (56%).

Therefore, the primary aim of this study is to prospectively investigate the current bleeding tendency of children and adults with VWD.

Inclusion Criteria:

• Historically lowest VWF:Ag and/or VWF:RCo and/or VWF:CB ≤ 0.30 IU/mL and/or FVIII:C ≤ 0.40 IU/mL
• Treatment at a Hemophilia treatment center in the Netherlands
• All types of VWD
• All ages

Exclusion Criteria:

- Other known bleeding disorders present.

Von Willebrand disease patients known in a Hemophilia Treatment Center in the Netherlands