Joint disease status of severe and moderate haemophilia patients at the Beijing Children's Hospital: early onset and rapid increasing severity of arthropathy in 90% of patients by 6 years of age.

*Hemophilia Work Group, Beijing Children’s Hospital affiliated to Capital Medical University, Beijing, China; †Children’sHospital of Eastern Ontario, University of Ottawa, Ottawa, ON; ‡Foothills Hospital, University of Calgary, Calgary, AB;and §The Hospital for Sick Children, University of Toronto, Toronto, ON, Canada