Haemophilia A
Approximately one in every 5000 men are born with haemophilia A. Haemophilia is referred to as an “X-linked recessive condition” 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 and mostly unaffected, but some carriers may experience minor symptoms of the mild form of haemophilia e.g. heavy periods, may bleed more following major trauma or a major operation). 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. The clinical symptoms are similar to haemophilia A and only a blood test can show whether a patient has haemophilia A or B. 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 antibodies - proteins developed by the body which bind and may neutralise the effect of a substance. Antibodies, also known as inhibitors in haemophilia, to FVIII or FIX can develop in patients with haemophilia after replacement therapy with the missing coagulation factor. Inhibitors occur in up to 30% of haemophilia A and 3-5% of haemophilia B patients. Most of these antibodies develop during childhood. Clinically, most inhibitors are detected when patients do not respond to standard replacement therapy with FVIII or FIX. The management of haemophilia patients with inhibitors is difficult because standard replacement therapies do not work. Agents that bypass the coagulation process which is inhibited by the antibody can be used to treat inhibitor patients.

HQMMA/N7/0914/0067. November 2014.