- n.either of two hereditary disorders in which the blood clots very slowly, due to a deficiency of either of two coagulation factors: haemophilia A, due to deficiency of Factor VIII (antihaemophilic factor); or haemophilia B, due to deficiency of Factor IX (Christmas factor). The patient may experience prolonged bleeding following any injury or wound, and in severe cases there is spontaneous bleeding into muscles and joints. Bleeding in haemophilia may be treated by recombinent-DNA-derived Factor VIII or plasma Factor VIII concentrate. Alternatively concentrated preparations of Factor VIII or Factor IX, obtained by freezing fresh plasma, may be administered (see cryoprecipitate). Haemophilia is controlled by a sex-linked gene, which means that it is almost exclusively restricted to males: women can carry the disease - and pass it on to their sons - without being affected themselves. The genes encoding factors VIII and IX have been used in gene therapy trials for haemophilia.• haemophiliac n.
Medical dictionary. 2011.