Haemophilia B - Clotting disorders

Haemophilia B

Definition

An inherited coagulation disorder resulting from a factor IX deficiency.

Incidence

1 in 30,000.

Age

Inherited

Sex

X linked; males only affected.

Aetiology/pathophysiology

Mutations on the X chromosome including deletions, point mutations and insertions. Factor IX is the last com-ponent of the intrinsic pathway .

Clinical features

Similar to haemophilia A with mild deficiency causing only bleeding post surgery and trauma. Severe deficiency presents in early life with recurrent joint and muscle bleeds.

Investigations

Activated partial thromboplastin time is raised, but correctable with 50% normal serum (i.e. not due to an inhibitor of coagulation) other coagulation measures are normal.

Factor XI levels are low.

Management

Treated with factor IX concentrates. Patients who develop antibodies to factor IX concentrates may be successfully treated with recombinant factor VIIa.