Approximately one in every 5,000 men are born with Hemophilia A. Hemophilia is referred to as an ‘X-linked condition’, meaning that the altered copy of the FVIII gene is located on the ‘female’ or ‘X’ chromosome. The daughter of a man with hemophilia will always be a carrier of hemophilia (carries the gene, but may experience some of the symptoms of hemophilia). The sons of a woman that carries the defective gene will have a 50% risk of suffering from hemophilia. The same woman’s daughters will have a 50% risk of being a carrier of hemophilia.
Hemophilia B is inherited in the same way as Hemophilia A, but it is six times less common at birth. Clinical manifestations are similar to Hemophilia A and it can only be differentiated from Hemophilia A through a blood test. It is sometimes called “Christmas disease” after the family name of the first patient – a Canadian – in whom it was diagnosed.
Hemophilia patients with inhibitors
Most patients that have Hemophilia 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 serious complication of the treatment of hemophilia is the development of ‘inhibitors’. ‘Inhibitors’ are antibodies to FVIII or FIX that can develop in patients with hemophilia following replacement therapy with the missing coagulation factor. The management of hemophilia patients with inhibitors is difficult. Clinically, most inhibitors are detected when patients fail to respond to standard treatment approaches used to treat patients without inhibitors. Inhibitor levels are measured in Bethesda units (BU).