Successful induction of immune tolerance in a patient with haemophilia B with inhibitor.

We describe successful induction of immune tolerance (IT) in a 10-month-old boy with severe haemophilia B. Urticaria developed soon after starting prophylactic treatment and was associated with an inhibitor at 7 Bethesda units mL(-1). Initially, we tried low dose factor IX therapy to induce IT with only a transient effect. The patient experienced an intracranial haemorrhage. A simple bolus dose of FIX eradicated the inhibitor. Thereafter he has been free from inhibitor and nephrotic syndrome for more than 5 years, although he receives FIX three times a week.