An inherited disorder of blood COAGULATION which results in prolonged bleeding even after minor injury. There is a deficiency of factor VIII, an essential clotting factor in the coagulation cascade – the complex series of biochemical events that is provoked by injury of the wall of a blood vessel and leads to the formation of a blood clot that checks bleeding. Haemophilia is a sex-linked recessive disorder though a small number of cases arise by spontaneous mutation. (see GENETIC DISORDERS). Thus, if females carry the disease, one-half of their sons will be affected and one-half of their daughters will be carriers. The sons of male haemophiliacs are unaffected (because their X chromosome is from their mother) but their daughters will be carriers.

Haemophilia affects approximately 1:4,000 of the UK population but only 1:20,000 severely. Severity of the disease depends upon how much factor VIII activity is present. Less than 1 per cent and there will be spontaneous bleeding into joints and muscles; 1–5 per cent and there will be occasional spontaneous bleeding and severe bleeding after minor injury; 5–25 per cent and there will be severe bleeding only after major injury. Before treatment was available, severe haemophiliacs suffered from acute pain and deformity from bleeds into joints and muscles. Bleeding also occurred into the gut, kidneys and brain, and few survived past adolescence.

Clotting factor concentrates may be kept in domestic refrigerators, and haemophiliacs can use it to abort minor bleeds by reconstituting it and injecting it intravenously. More severely affected patients may use it up to every few days on a regular basis in an attempt to prevent bleeding.

With treatment, most haemophiliacs lead normal lives, although dangerous or contact sports are best avoided. Before donors of blood were screened for HEPATITIS B and C or for HIV infection (see AIDS/HIV), some 4,800 sufferers receiving factor VIII in the UK were unwittingly infected with hepatitis C, and 1,200 with HIV. Blood products are now treated to eliminate viruses, and genetically engineered ‘recombinant’ clotting factors have come into use, thus removing the risks.

Patients with deficiency of factor IX have similar symptoms and are often referred to as having haemophilia B. The UK has a National Haemophilia Register and each registered sufferer carries a card with details about his condition.