Haemophilia B

What is Haemophilia B?

Haemophilia B involves a genetic defect causing abnormality of blood clotting. Normal blood contains a range of special proteins and chemicals that cause blood to clot quickly if blood vessels are damaged. This occurs due to a sequence of events known as the 'coagulation cascade', involving a series of reactions between different coagulation 'factors'. The end result is a mesh of protein called 'fibrin', which is the solid part of a clot, and plugs up the damaged vessel. In Haemophilia B, levels of a coagulation factor called Factor IX are reduced. This occurs due to defects in the gene coding for this protein.

Statistics on Haemophilia B?

The prevalence of harmophilia B is about 1 in 30,000 in the male population. It is only present in males because the gene for Factor IX is on the X chromosome; males only inherit one X chromosome, and so if this has the defect, then they will suffer haemophilia. Females inherit two X chromosomes, and so even if one has the defect, they will not suffer from haemophilia, as the other chromosome has a normal Factor IX gene. Females with one abnormal X chromosome are called 'carriers'. If a female carrier has a son, he has a 50% chance of having haemophilia, and a daughter has a 50% chance of being a carrier. All daughters of haemophiliacs are carriers and the sons are normal.

Risk Factors for Haemophilia B

As explained above, a family history is clearly a predisposing factor for haemophilia. In addiotion, about one-third of cases are 'sporadic', meaning that the genetic defect occurs for unknown reasons, without being passed on from the patient's parents.

Progression of Haemophilia B

As the disease arises from an abnormality in a gene coding for a protein that is important to coagulation throughout life, haemophilia is an immediate, constant and unremitting disease. However, cases vary in severity, depending on the level of Factor IX in the body. In milder cases, diagnosis may not be made until quite late in life. In addition, effective treatment is available, meaning that patients may show considerable improvement once this has begun.

How is Haemophilia B Diagnosed?

Full blood examination- this will usually be normal, apart from lowered haemoglobin if the patient has become anaemic due to blood loss.

Coagulation studies - the following important tests of blood coagulation and coagulation factors will be altered: PTTK (APPT) - increased; Factor IX - markedly decreased.

Prognosis of Haemophilia B

The most frequent cause of death in patients with severe haemophilia was cerebral haemorrhage; it is now AIDS. Although HIV transmission by blood transfusion is now very rare in the developed world, HIV was transmitted to many haemophiliacs by coagluation facor concentrates between 1979 and 1985.

How is Haemophilia B Treated?

Not surprisingly, the treatment for haemophilia B is replacement of Factor IX. This is made from donated blood.

Haemophilia B References

[1] Kumar P, Clark M. Clinical Medicine. Fourth Ed. WB Saunders, 1998. p 406[2] Talley NJ, O'Connor S. Clinical examination. Third Ed. MacClennan & Petty, 1996. p227