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Haemophilia, von Willebrand disease and other coagulation defects
Background
The conditions covered in this entry are haemophilia A, haemophilia B (Christmas disease), von Willebrand disease (VWD) and some other coagulation defects.
The haemophilias (hemophilias - US) are a group of inheritable blood disorders characterised by various defects in the blood clotting system. The clotting factors present in blood were initially known by Roman numerals, numbered from I to XIII. More recently described factors have been given names and some deficiencies are associated with excessive, rather than reduced, blood coagulation. Factor VIII is deficient in classical haemophilia, also known as haemophilia A. Factor IX is deficient in haemophilia B (also known as Christmas disease). Von Willebrand factor is deficient in VWD and this results in a failure of platelet and vessel wall function with an associated reduction in factor VIII clotting activity.
Haemophilia occurs in about 1 in 10,000 of the population in the UK, with haemophilia A (six thousand patients) being five times as frequent as haemophilia B (one thousand two hundred and fifty patients). Both conditions are sex-linked so that it is almost always males who are affected. VWD occurs equally in males and females and about seven thousand five hundred patients are registered in the UK but the real number of affected people is certainly much greater. These conditions affect all racial groups and occur worldwide.
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