Haemophilia B is due to a deficiency of Factor IX. It is also known as Christmas Disease (after the person in whom the disease was first identified). The genetic defect is sex-linked and approximately 1 in 50,000 are affected. If untreated, patients with severe deficiencies may have frequent spontaneous bleeding into joints and muscles; they bleed excessively during minor surgery (e.g. tooth extraction) and may suffer life-threatening bleeding from trauma or even relatively minor injury. Replacement of the missing Factor IX corrects the bleeding problem.
Table 1 - Correlation of coagulation factor activity and severity in Haemophilia A and B
|Coagulation Factor Activity (% normal*)||Clinical Manifestation|
|≤1||Severe - frequent spontaneous bleeds from early life, joint deformity and crippling if not adequately treated|
|>1 to <5||Moderate - post-traumatic bleeding, occasional spontaneous bleeds|
|≥5||Mild - post-traumatic bleeding|
|* Normal is 100% and is defined as 100 international units (IU) of the factor per dL of blood. 'Normal' coagulation factor activity can range from 50 - 200%. About one-third of carriers have low or subnormal activity. In normal pregnancy, activity levels may exceed 200%.|