‘Haemophilia’ is a term referring to a group of genetically transmitted life-long blood clotting disorders which are caused by a defect in one or more of the plasma clotting factors. The most common are sex-linked recessive disorders, haemophilia A (classic haemophilia) and haemophilia B (Christmas disease), which are due to an isolated deficiency of the clotting activity of factor VIII or of factor IX, respectively. People with these disorders suffer bleeding into soft tissues, for example, joints, muscles or internal organs, which can happen after trauma or spontaneously. These bleeds can be very painful, and repeated episodes lead to weakening and crippling of joints. Bleeds into internal organs and the brain can be life-threatening. There is no cure for haemophilia.

Another common blood disorder is von Willebrand's disease or vascular haemophilia. It is an autosomal dominant genetic disorder, i.e. it is not sex-linked and affects both men and women. It is due to a combination of an abnormal factor VIII molecule with abnormal platelet function. Many problems related to treatment and its complications, as well as social and psychological problems are similar to those found in haemophilia A and B.

Genetics and clinical manifestation

Haemophilias A and B are genetically transmitted as follows: an affected woman carries a defective gene on one of her X chromosomes, which she can pass to any of her children.