Congenital
haemophilia
Haemophilia A
Approximately one in every 5000 men are born with haemophilia A. Haemophilia is referred to as an ‘X-linked recessive condition’, meaning that the defective FVIII gene is located on the ‘female’ or ‘X’ chromosome. The daughter of a man with haemophilia will always be a carrier of haemophilia (carries the gene, but does not suffer from the symptoms of haemophilia). The sons of a woman that carries the defective gene will have a 50% risk of suffering from haemophilia. The same woman’s daughters will have a 50% risk of being a carrier of haemophilia.
Haemophilia B
Haemophilia B is inherited in the same way as haemophilia A, but it is five times less common. Clinical impact is similar to Haemophilia A and it can only be differentiated from haemophilia A through a blood test. It is sometimes called Christmas disease after the family name of the first patient in whom it was diagnosed.
Haemophilia patients with inhibitors
Most patients that have haemophilia A or B are treated by replacing their missing coagulation factor with FVIII or FIX that is either derived from plasma or developed using recombinant technology. One of the most feared complications of the treatment of haemophilia is the development of ‘inhibitors’. ‘Inhibitors’ are antibodies to FVIII or FIX that can develop in patients with haemophilia following replacement therapy with the missing coagulation factor. The incidence of inhibitors complicating treatment of haemophilia A and B is approximately 30% in haemophilia A and 3 to 5% in haemophilia B patients. Most of these antibodies develop during childhood. The management of haemophilia patients with inhibitors is difficult. Clinically, most inhibitors are detected when patients fail to respond to standard replacement therapy. Inhibitor levels are measured in Bethesda units (BU).
